Sleep-wake behaviour during the first 12 months of life and associated factors: a systematic review

Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=gecd20 Early Child Development and Care ISSN: 0300-4430 (Print) 1476-8275 (Online) Journal homepage: https://www.tandfonline.com/loi/gecd20 Sleep-wake behaviour during the first 12 months of life and associated factors: a systematic review Cláudia Castro Dias & Bárbara Figueiredo To cite this article: Cláudia Castro Dias & Bárbara Figueiredo (2019): Sleep-wake behaviour during the first 12 months of life and associated factors: a systematic review, Early Child Development and Care To link to this article: https://doi.org/10.1080/03004430.2019.1582034 Published online: 06 Mar 2019. Submit your article to this journal View Crossmark data REVIEW ARTICLE Sleep-wake behaviour during the first 12 months of life and associated factors: a systematic review Cláudia Castro Dias and Bárbara Figueiredo School of Psychology, University of Minho, Braga, Portugal ABSTRACT This paper aims to provide a systematic review of the literature on the associated factors with infant sleep-wake behaviour during the first 12 months of life, namely (1) the factors positively and negatively associated with sleep-wake behaviour and (2) the factors positively and negatively affected by sleep-wake behaviour. This systematic review was based on a standard protocol constructed according with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement and included 146 papers. Two typologies of factors were found in the literature: factors positively and negatively associated with infant sleep-wake behaviour and effects of sleep-wake behaviour. Different factors were identified as being positively and negatively associated with the different sleep-wake behaviours and positively and negatively affected by the different sleep-wake behaviours during the first 12 months of life. Some inconsistent results could be explained by methodological differences between the studies. ARTICLE HISTORY Received 19 December 2018 Accepted 10 February 2019 KEYWORDS Sleep-wake behaviour; infant; positive factors; negative factors Literature has been shown that infant sleep-wake behaviour is associated with several factors: infant factors, namely temperament (Kaley, Reid, & Flynn, 2012; Sorondo & Reeb-Sutherland, 2015) and parental factors, namely parental psychopathology (Sadeh, Tikotzky, & Scher, 2010). Moreover, a recent review pointed for a bidirectional association, arguing that parental factors influenceandareinfluenced by infant sleep-wake behaviour, within the context of a transactional model (Sadeh et al., 2010). The transactional model argues that the bidirectional associations between parental factors and infant sleep-wake behaviors are complex and dynamic (Sadeh et al., 2010). Several changes and high individual stability have been observed in infant sleep wake-behaviour during the first months (Figueiredo, Dias, Pinto, & Field, 2016), being imperative to identify the factors that could be associated with sleep-wake behaviour during the first 12 months of life. The identification of these factors could help to the prevention and early intervention on infant’s sleep problems and to guide future research on infant sleep-wake behaviour. To our knowledge, there is no systematic review in the literature identifying the factors positively and negatively associated with sleep-wake behaviour during the first 12 months of life. This paper aims to provide a systematic review of the literature on the associated factors with infant sleepwake behaviour during the first 12 months of life, namely (1) the factors positively and negatively associated with sleep-wake behaviour and (2) the factors positively and negatively affected by sleep-wake behaviour. © 2019 Informa UK Limited, trading as Taylor & Francis Group CONTACT Cláudia Castro Dias [email protected] Universidade do Minho, Escola de Psicologia, Campus de Gualtar, 4700-057 Braga, Portugal EARLY CHILD DEVELOPMENT AND CARE https://doi.org/10.1080/03004430.2019.1582034 Materials and methods This systematic review was based on a standard protocol constructed according with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement (Moher, Liberati, Tetzlaff, & Altman, 2009). Literature search The authors performed a literature search to identify manuscripts referring infant sleep-wake behaviour published between June 1996 and June 2016. The search covered three databases: MEDLINE, ISIs Web of Knowledge, and PsycINFO using the keywords: sleep AND infant OR baby. Considering the spoken languages by the two authors, English, Portuguese, Spanish, Italian, and French written articles were included. The first author performed the electronic search and the second author independently replicated it. To select potentially relevant papers, the two authors independently analyzed the titles and the abstracts (n= 8610) obtained in the electronic search and excluded the manuscripts that did not study factors associated with infant sleep-wake behaviour (n= 8244). The manuscripts whose abstracts assessed factors associated with infant sleep-wake behaviour (n= 367) were then independently analyzed for inclusion/exclusion criteria by the two authors, leading to the exclusion of 220 manuscripts. Through all the literature search process, the two authors reached consensus through discussion. Inclusion and exclusion criteria This systematic review included only original empirical articles addressing factors associated with sleep-wake behaviour during the first 12 months of life. The authors used the following inclusion criteria: (a) original studies; (b) assessing factors associated with sleep-wake behaviour; (c) during the first 12 months of life. Studies were excluded based on the following exclusion criteria: (a) non-original research (e.g. literature reviews, systematic reviews, or meta-analysis); (b) studies assessing infants above 12 months or studies that did not indicate infant’s age; (c) sleep interventions or clinical trials; (d) case reports or single case studies. Quality assessment All included studies were scored for quality, based on the system of Downs and Black (Downs & Black, 1998), a Quality Index that evaluates the methodological quality of randomized and non-randomized studies. The Quality Index is comprised of 27 items that are aggregated in 5 sub-scales. Fourteen items, from the total 27, were selected to score all the studies that were included in this systematic review, with a maximum possible score of 15. Manuscripts scoring >10 in the Quality Index were considered good, those scored between seven and 10 were considered moderate, and those scoring < seven were considered poor. Data extraction One author extracted the data from the studies to 2 data sheets (Tables 1 and 2) and the other author reviewed the data. The data sheets were organized according with (1) factors typology, namely: factors positively and negatively associated with infant sleep-wake behaviour and factors positively and negatively affected by infant sleep-wake behaviour and (2) the publication year. This systematic review included the different sleep-wake behaviors studied in the literature: sleep duration (number of hours that infants spend sleeping), Wake After Sleep Onset (WASO) (number of hours that infants spend awake during the night), sleep periods (number of sleep episodes) and night wakings (number of wakings during the night), sleep latency (time infants take to fall asleep), longest 2C. C. DIAS AND B. FIGUEIREDO Table 1. Factors positively and negatively associated with infant sleep-wake behaviour during the first 12 months of life. First author Year of publication Country Design Associated factor N Age (months) Sleep measure Sleep-wake behaviour Main result Factors positively associated with infant sleep-wake behaviour during the first 12 months of life Blair et al. (2012) UK L Birth order 11478 6 months Q SD (24 h) SD (24 h) at 6 months not associated with number of siblings Kaley et al. (2012) UK CS Birth order 77 1–2 months D SD (24 h, day, night), NW ↑SD (24 h, day) at 1–2 months in non-first-time infants NW not associated with birth order Kozyrskyj, Kendall, Zubrick, Newnham, and Sly (2009) Australia L Birth order 2398 12 months QNW ↑NW at 12 months associated with ↑siblings Santos, Mota, and Matijasevich (2008) Brazil L Birth order 3907 0 and 12 months INW ↑NW at 12 months in non-first-born infants So, Michael Adamson, and Horne (2007) Australia L Birth order 20 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 months Combined measures: A and D SD (24 h, day, night), NW SD (24 h, day, night) and NW at 1, 2, 3, 4, 5, 6, 8, 9, 10, 11, and 12 months not associated with birth order ↓SD (night) at 7 months (measured by D) in non-first-born infants Quillin (1997) USA CS Birth order 44 1 month D SD (24 h, night), NW, SP (24 h) SD (24 h, night), NW, and SP (24 h) at 1 months not associated with birth order Blair et al. (2012) UK L Ethnicity 11478 6 months Q SD (24 h) ↓SD (24 h) at 6 months in non-white infants Santos, Matijasevich, and Domingues (2012) Brazil CS Ethnicity 885 3 months INW ↑NW at 3 months in non-white infants Nevarez, Rifas-Shiman, Kleinman, Gillman, and Taveras (2010) USA L Ethnicity 1676 6, and 12 months Q SD (24 h) ↓SD (24 h) at 6 and 12 months in non-white infants Bathory et al. (2016) USA CS Parental education 557 9 months Q SD (day, night) ↓SD (night) associated with ↓parental health literacy SD (day) not associated with parental health literacy Blair et al. (2012) UK L Parental education 11478 6 months Q SD (24 h) SD (24 h) at 6 months not associated with maternal education and paternal social class Kozyrskyj et al. (2009) Australia L Parental education 2398 12 months Q NW NW at 12 months not associated with maternal education Nevarez et al. (2010) USA L Parental education 1676 6, and 12 months Q SD (24 h) ↓SD (24 h) at 6 and 12 months associated with ↓maternal education Palmstierna, Sepa, and Ludvigsson (2008) Sweden L Parental education 16467 12 months QNW ↑NW at 12 months associated with ↑parental theoretical education Orsi et al. (2015) Brazil L NICU characteristic 13 0 months PSD (24 h, day, and night) ↑SD (24 h and day) associated with reduced sensory and environmental stimuli SD (night) not associated with sensory and environmental stimuli Touchette et al. (2013) Canada L Genetic/ environment (twins) 995 6 months Q SD (day, night) ↑SD (night) at 6 months associated with genetic influences SD (day) at 6 months associated with environmental influences Tourula, Isola, Hassi, Bloigu, and Rintamäki (2010) Finland CS Environment 34 3 months O SD (day) ↑SD (day) at 3 months in outdoor environment (Continued) EARLY CHILD DEVELOPMENT AND CARE 3 Table 1. Continued. First author Year of publication Country Design Associated factor N Age (months) Sleep measure Sleep-wake behaviour Main result Bhat et al. (2006) UK CS Sleep position 24 0 months PSD (day), SP (day), SE ↑SD (day), ↓SP (day), and ↑SE at 0 months associated with prone position Utkun, Öndoğan, Yalaz, and Yıldırım Sözmen (2015) Turkey CS Clothes’fabrics 8 6–12 months NS SD (night) ↑SD (night) at 6–12 months associated with wearing Ö4 fabric Brand, Furlano, Sidler, Schulz, and Holsboer-Trachsler (2011) Switzerland L Cortisol 16 2 and 3 months A SD (day, night), A (day, night) ↑SD (night) and ↑NW at 3 months associated with ↑cortisol secretion in infants with colic Lucas-Thompson et al. (2009) USA L Cortisol 92 6 and 12 months QNW ↑NW at 6 and 12 months associated with ↑cortisol response to stress at 6 and 12 months Larson, White, Cochran, Donzella, and Gunnar (1998) USA CS Cortisol 78 2–4 months D SD (night) ↑SD (night) at 2–4 months associated with early morning peak in cortisol levels Shinohara and Kodama (2011) Japan CS Melatonin 67 3–5 months D SD (night), NW, SP (day), LSP (24 h) ↑SD (night) at 3–5 months associated with ↓morning melatonin levels at 3–5 months Pennestri et al. (2015) Canada L Attachment 138 6, 12 months Q SD (night), NW, SL (night), LSP (night), BT ↓SD (night), ↑NW and ↑BT at 6 and 12 months in disorganized children than in secure and ambivalent children ↓LSP (night) at 12 months in disorganized children than in secure and ambivalent children SL (night) not associated with attachment Zentall, Braungart-Rieker, Ekas, and Lickenbrock (2012) USA L Attachment 46 7, 12 months QNW ↓NW from 7 to 12 and 14 months in infants with secure attachment NW at 7 months not associated with attachment Scher (2001a) Israel CS Attachment 94 12 months A SD (night), NW, LSP (night), SL (night) SD (night), NW, LSP (night), and SL (night) at 12 months not associated with attachment style de Graag, Cox, Hasselman, Jansen, and de Weerth (2012) The Netherlands L Mother–infant relationship 84 1 and 5 months D LSP (24 h) ↑LSP (24 h) from 1 to 5 months associated with ↑flexible mother-infant interactions at 5 months Schwichtenberg, Anders, Vollbrecht, and Poehlmann (2011) USA L Mother-infant relationship 134 4 and 9 months D SD (day), SP (day) ↑SD (day) at 9 months associated with ↑maternal negative affect and behaviour at 4 and 9 months ↑SP (day) at 4 and 9 months associated with ↑optimal maternal interactive behaviors at 24 months Scher (2001b) Israel CS Mother-infant relationship 37 12 months A SD (night), NW, SE, BT ↑NW at 12 months associated with ↑mother-infant relationship ↑SE at 12 months associated with ↑infant responsiveness, but not with other mother-infant interaction dimensions SD (night) and BT at 12 months not associated with motherinfant interaction Factors negatively associated with infant sleep-wake behaviour during the first 12 months of life Saenz, Yaugher, and Alexander (2015) USA L Gender 47 3–4months A SD (night), SE SD (night) and SE at 3–4 months not associated with gender Blair et al. (2012) UK L Gender 11478 6 months Q SD (24 h) ↓SD (24 h) at 6 months in boys Kaley et al. (2012) UK CS Gender 77 1–2 months D SD (24 h, day, night), NW ↑NW at 1–2 months in boys SD (24 h, day, night) not associated with gender 4C. C. DIAS AND B. FIGUEIREDO Santos et al. (2012) Brazil CS Gender 885 3 months INW ↑NW at 3 months in boys Lampl and Johnson (2011) USA L Gender 23 0–12 months D SD (24 h), SP (24 h), LSP (24 h) ↑SP (24 h) and ↓LSP (24 h) at 0–12 months in boys SD (24 h) not associated with gender Kozyrskyj et al. (2009) Australia L Gender 2398 12 months Q NW NW at 12 months not associated with gender Santos et al. (2008) Brazil L Gender 3907 0 and 12 months INW ↑NW at 12 months more in boys Anuntaseree, Mo-Suwan, Vasiknanonte, Kuasirikul, and Choprapawan (2008) Thailand CS Gender 3172 3 months INW ↑NW at 3 months in boys So et al. (2007) Australia L Gender 20 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 months Combined measures: A and D SD (24 h, day, night), WASO, SP (day), LSP (night) ↓SD (day) at 1 (measured by A and D) and 2 (measured by A) months in boys SD (day) at 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 months not associated with gender SD (24 h, night), WASO, and LSP (night) at 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 months not associated with gender Thomas and Foreman (2005) USA CS Gender 37 1–2 months D SD (24 h), SP (24 h), LSP (24 h) ↓SD (24 h) at 1–2 months in boys SP (24 h), LSP (24 h) at 1–2 months not associated with gender Goodlin-Jones, Burnham, Gaylor, and Anders (2001) USA CS Gender 80 3, 6, 9, or 12 months V NW, LSP (night) ↑LSP (night) in girls NW not associated with gender Bach, Telliez, Leke, and Libert (2000) France CS Gender 38 1 month EEG SD (24 h), LSP (24 h) ↓SD (24 h), and ↓LSP (24 h) at 1 month in boys Blair et al. (2012) UK L Parents’sociodemographic factors 11478 6months Q SD (24 h) ↓SD (24 h) at 6 months in infants of older mothers Kozyrskyj et al. (2009) Australia L Parents’sociodemographic factors 2398 12 months QNW ↑NW at 12 months in infants of mothers older than 20 years NW at 12 months not associated with maternal marital status Nevarez et al. (2010) USA L Parents’sociodemographic factors 1676 6, and 12 months Q SD (24 h) ↓SD (24 h) at 6 and 12 months associated with infants of single/divorced parents Palmstierna et al. (2008) Sweden L Parents’sociodemographic factors 16467 12 months QNW ↑NW at 12 months associated with non-Swedish parents and marginally associated with single parent at birth Tomalski et al. (2013) UK CS Socio-economic factors 45 6–9 months Q SD (24 h, day, night), WASO, NW SD (24 h, day, night), WASO, and NW not associated with income Nevarez et al. (2010) USA L Socio-economic factors 1676 6 and 12 months Q SD (24 h) ↓SD (24 h) at 6 and 12 months associated with ↓household incomes, and ↑household members Kozyrskyj et al. (2009) Australia L Socio-economic factors 2398 12 months Q NW NW at 12 months not associated with financial problems and income Santos et al. (2008) Brazil L Socio-economic factors 3907 0 and 12 months INW ↑NW at 12 months in infants whose mothers were employed during pregnancy (Continued) EARLY CHILD DEVELOPMENT AND CARE 5 Table 1. Continued. First author Year of publication Country Design Associated factor N Age (months) Sleep measure Sleep-wake behaviour Main result Fouts, Roopnarine, and Lamb (2007) USA CS Socio-economic factors 62 3–4 months O SD (day), SP (day), LSP (day) ↑SP (day) and ↓LSP (day) at 3–4 months in infants from ↓ socioeconomic status SD (day) at 3–4 months not associated with socioeconomic status Cohen, Atun-Einy, and Scher (2012) Israel CS Environment 34 7 months A SD (night), WASO, NW, BT, WT ↑BT at 7 months in winter months SD (night), WASO, and NW and WT at 7 months not associated with seasonal effects Bottino et al. (2012) USA CS Environment 1226 12 months Q SD (24 h) ↓SD (24-hour) at 12 months associated with ↑urban environments Harrison (2004) UK L Environment 66 1, 2, 3 months Combined measures: D and A SD (night) ↓SD (night) at 1 month associated with ↓exposure to light during the afternoon Kozyrskyj et al. (2009) Australia L Environment 2398 12 months QNW ↑NW at 12 months associated with mothers not smoking at 12 months NW at 12 months not associated with exposure to stressful events Santos et al. (2012) Brazil CS Gestational exposure 885 3 months I NW NW at 3 months not associated with gestational exposure to caffeine ↑NW at 3 months in infants exposed to smoke and alcohol during pregnancy Kozyrskyj et al. (2009) Australia L Gestational exposure 2398 12 months QNW ↑NW at 12 months associated with ↑stressful events during early pregnancy and no exposure to smoke during pregnancy Lehnkering, Korte, and Siegmund (2009) Germany CS Gestational exposure 22 0 months Combined measures: A and D SD (24 h) SD (24 h) at 0 months not associated with gestational exposure to smoke Hanft, Burnham, Goodlin-Jones, and Anders (2006) USA L Gestational exposure 34 1, 3, 6, 9, and 12 months V SD (night), WASO, NW, LSP (night) ↓SD (night) at 3, 6, and 12 months and ↓LSP (night) at 6 months in infants exposed to substances during pregnancy WASO and NW at 1, 3, 6, 9, and 12 months, SD (night) at 1 and 9 months and LSP (night) at 1, 3, 9, and 12 months not associated with gestational exposure to substances Korte, Hoehn, and Siegmund (2004) Germany L Delivery mode 57 0 months A SD (24 h, day, night), SP (day) SD (24 h, day, night) at 0 months not associated with delivery mode ↑SP (day) at 0 months in infants born by planed C-section Huang, Paiva, Hsu, Kuo, and Guilleminault (2014) China CS Gestational age 191 6 months Q SD (day, night) NW ↑SD (day, night) and ↑NW at 6 months in preterm infants Guyer et al. (2015) Switzerland L Gestational age 48 1, 3, and 6 months D SD (24 h, day, night), LSP (night) ↑SD (night) and ↑LSP (night) at 1, 3, and 6 months in premature infants SD (24 h, day) at 1, 3, and 6 months not associated with gestational age Asaka and Takada (2010) Japan CS Gestational age 28 12 months A SD (24 h, day, night), WASO, NW ↓SD (night) at 12 months in preterm infants SD (24 h, day), WASO, and NW at 12 months not associated with gestational age 6C. C. DIAS AND B. FIGUEIREDO Kozyrskyj et al. (2009) Australia L Gestational age 2398 12 months QNW ↓NW at 12 months in preterm infants Volkovich, Ben-Zion, Karny, Meiri, and Tikotzky (2015) Israel L Feeding method 153 3 and 6 months Combined measures: A and D NW ↑NW at 3 and 6 months associated with breastfeeding at 3 months Brown and Harries (2015) UK CS Feeding method 715 6–12 months QNW NWat6–12 months not associated with feeding method Huang et al. (2016) China L Feeding method 524 1, 3, 5, and 8 months D SD (24 h, day, night), NW, SP (day), LSP (night) ↓SD (24 h, day) in the first 8 months in exclusively and partially breastfed infants ↑NW in the first 8 months in exclusively and partially breastfed infants than in exclusively formula fed SD (night), SP (day) and LSP (night) not associated with feeding method Tikotzky et al. (2015) Israel L Feeding method 57 3 and 6 months Combined measures: A, D, and Q NW ↑NW at 6 months associated with breastfeeding at 3 and 6 months Hughes, Gallagher, and Hannigan (2015) Ireland CS Feeding method 11134 9 months Q SD (night), NW ↓SD (night) and ↑NW at 9 months associated with ↑ breastfeeding rates Hysing et al. (2014) Norway L Feeding method 55831 6 months QNW ↑NW at 6 months associated with breastfeeding Galbally, Lewis, McEgan, Scalzo, and Islam (2013) Australia CS Feeding method 4507 3–19 months QNW ↑NW at 3–19 months associated with breastfeeding at 6 months Mindell, Du Mond, Tanenbaum, and Gunn (2012) USA L Feeding method 92 3, 6, 12 months Q SD (night), NW, SP (day), LSP (24 h), SL (night) ↑NW and ↑SP (day) at 3–12 months associated with breastfeeding SD (night), LSP (24 h), and SL (night) at 3–12 months not associated with feeding method Ramamurthy et al. (2012) Asia Pacific Region CS Feeding method 4602 0–12 months Q SD (24 h, day, night), NW, SP (day), SL (night), LSP (night), BT, WT ↑SD (24-hour, day), ↑NW, ↓LSP (night), ↑SP (day), and ↑BT from 0 to 6 months in breastfed infants ↑NW, and ↓LSP (night) from 6 to 12 months in breastfed infants SD (night) and WT not associated with breastfeeding Demirci, Braxter, and Chasens (2012) USA CS Feeding method 77 6–11 months Q SD (24 h, day, night), SL (night) SD (24 h, day, night) and SL (night) at 6–11 months not associated with feeding method Kaley et al. (2012) UK CS Feeding method 77 1–2 months D SD (24 h, day, night), NW ↑NW at 1–2 months in breastfed infants SD (24 h, day, night) at 1–2 months not associated with feeding method Engler, Hadash, Shehadeh, and Pillar (2012) Israel CS Feeding method 94 2–4 months Q SD (night), NW, SL (night) ↑NW and marginally ↑SD (night) at 2–4 months associated with breastfeeding SL (night) not associated with feeding method Lampl and Johnson (2011) USA L Feeding method 23 0–12 months D SD (24 h), SP (24 h), LSP (24 h) ↑SP (24 h) and ↓LSP (24 h) at 0–12 months associated with breastfeeding SD (24 h) not associated with feeding method Nevarez et al. (2010) USA L Feeding method 1676 6, and 12 months Q SD (24 h) SD (24 h) at 6 and 12 months not associated with feeding method at 6 months Kozyrskyj et al. (2009) Australia L Feeding method 2398 12 months QNW ↑NW at 12 months associated with ↑exclusive breastfeeding duration (Continued) EARLY CHILD DEVELOPMENT AND CARE 7 Table 1. Continued. First author Year of publication Country Design Associated factor N Age (months) Sleep measure Sleep-wake behaviour Main result Anuntaseree et al. (2008) Thailand CS Feeding method 3172 3 months INW ↑NW at 3 months associated with exclusive breastfeeding Mindell, Meltzer, Carskadon, and Chervin (2009) USA CS Feeding method 1473 0–11 months I SD (night), NW, SL (night) ↑NW at 0–11 months associated with breastfeeding SD (night) and SL (night) not associated with feeding method Schwichtenberg and Poehlmann (2009) USA CS Feeding method 128 4 months D SD (night), NW ↓SD (night) and ↑NW at 4 months in breastfed preterm infants DeLeon and Karraker (2007) USA CS Feeding method 41 9 months D SD (24 h, day, night), WASO, NW, SP (day) ↓SD (night), ↑WASO and ↑NW at 9 months associated with breastfeeding SD (24 h, day), and SP (day) not associated with feeding method Cubero et al. (2005) Spain CS Feeding method 16 3 months A SD (night), SL (night), SE ↑SD (night) and ↑SE at 3 months associated with breastfeeding SL (night) not associated with feeding method Morgan, Lucas, and Fewtrell (2004) UK L Feeding method 1694 6, 9 months Q SD (night) ↓SD (night) at 9 months associated with ↑breastfed duration in term infants SD (night) at 9 months not associated with breastfeeding duration in term infants Quillin and Glenn (2004) USA CS Feeding method 33 1 month D SD (24 h, night), NW, SP (24 h) ↓SD (24 h) at 1 month associated with breastfeeding SD (night), NW and SP (24 h) not associated with feeding method Ball (2003) UK L Feeding method 253 1, 3 months DNW ↑NW at 1 and 3 months associated with breastfeeding Lee (2000) Korea CS Feeding method 188 0–4months D SD (24 h), LSP (night) ↑SD (24 h) and ↓LSP (night) at 0–4 months associated with breastfeeding Thomas (2000) USA CS Feeding method 37 1 month D SD (24 h, day, night), WASO SD (24 h, day, night), and WASO not associated with feeding method in preterm infants Wolke, Söhne, Riegel, Ohrt, and Österlund (1998) Finland/ Germany L Feeding method 5969 5 months INW ↑NW at 5 months associated with breastfeeding Quillin (1997) USA CS Feeding method 44 1 month D SD (night), NW, SP (24 h) ↓SD (night) and ↑NW at 1 month in breastfed infants SP (24 h) at 1 month not associated with feeding method Brown and Harries (2015) UK CS Diet 715 6–12 months QNW NWat6–12 months not associated with milk feeds, age of introduction of solids, number of complementary meals per day, and daytime feeds. Nevarez et al. (2010) USA L Diet 1676 6, and 12 months Q SD (24 h) ↓SD (24 h) at 12 months associated with introduction of solids <4 months Thomas and Foreman (2005) USA CS Diet 37 1–2 months D SD (24 h), SP (24 h), LSP (24 h) ↓SD (24 h), ↑SP (24 h), and ↓SD (24 h) associated with ↑ infant feedings Telliez, Bach, Leke, Chardon, and Libert (2002) France CS Diet 17 1 month PSD (day) ↑SD (day) in the medium-chain triacylglycerol diet group Philbrook and Teti (2016) USA L Bedtime routines 109 1, 3 and 6 months V SD (night) ↓SD (night) from1 to 6 months associated with ↓arousing activities 8C. C. DIAS AND B. FIGUEIREDO Scher (2008) Israel CS Social emotional problems 52 10 months Combined measures: A and Q NW, SE ↑NW (measured by A, but not measured by Q) and ↓SE at 10 months associated with ↑maternal separation anxiety at 10 months Spruyt et al. (2008) Belgium L Social emotional problems 20 3, 6, 11, and 12 months Combined measures: A and D SD (day) ↑SD (day) at 12 months associated with ↓emotion regulation and ↓total behaviour development score DeLeon and Karraker (2007) USA CS Social emotional problems 41 9 months D SD (24 h, day, night), WASO, NW, SP (day) ↓SD (24 h, night), ↑WASO, ↑NW, ↑SP (day) at 9 months associated with ↑separation distress SD (night) not associated with separation distress Scher and Blumberg (1999) Israel L Social emotional problems 81 6 and 12 months QNW ↑NW at 12 months associated with ↑maternal separation anxiety Mindell and Lee (2015) Brazil CS Temperament 1351 3–13 months Q SD (night), SL (night), NW, SP (day), BT, WT ↑NW and ↓SP (day) associated with ↓bedtime, morning, and daytime mood ↑BT and ↓SD (night) associated with ↓daytime mood ↓SD (night) and ↑WT associated with ↓morning mood SL not associated with mood BT not associated with bedtime and morning mood WT not associated with bedtime and daytime mood SD (night) not associated with bedtime mood Sorondo and Reeb-Sutherland (2015) USA L Temperament 40 5, 9, and 12 months QSD (day, night), WASO, NW, SL (night) ↑SL (night) at 5 months and ↑WASO at 5, 9, and 12 months associated with negative reactivity at 5 months SD (day, night) and NW at 5, 9, and 12 months not associated with negative reactivity Kaley et al. (2012) UK CS Temperament 77 1–2 months D SD (24 h, day, night), NW ↑SD (day) at 1–2 months associated with positive temperament ↓SD (24 h, day, night) at 1–2 months correlated with temperament dimensions (activity, approach, intensity, and distractibility) NW at 1–2 months not associated with temperament dimensions Gibson, Gander, and Elder (2012) New Zealand CS Temperament 52 12 months A SD (night), SL (night), BT, WT ↓SL (night) at 12 months in infants more alert during the day ↑SD (night) and ↑WT at 12 months in infants in good mood in the morning ↓WT at 12 months in infants rated as tired at bedtime SD (night), BT, and WT at 12 months not associated with daytime alertness SL (night) and BT at 12 months not associated with morning mood SD (night), SL (night), and BT at 12 months not associated with tired at bedtime SD (night), SL (night), BT and WT at 12 months not associated with bedtime mood and bedtime problems Spruyt et al. (2008) Belgium L Temperament 20 3, 6, 11, and 12 months Combined measures: A and D SD (24 h, day, night) ↑SD (24 h) at 3 months associated with ↑approachability ↑SD (24 h) at 6 months associated with ↑rhythmicity and ↓ distractibility ↑SD (24 h) at 12 months associated with ↑rhythmicity and ↓ persistence (Continued) EARLY CHILD DEVELOPMENT AND CARE 15 Table 1. Continued. First author Year of publication Country Design Associated factor N Age (months) Sleep measure Sleep-wake behaviour Main result ↑SD (day) at 12 months associated with perceived negative mood ↑SD (night) at 3, 6 and 11 months associated with ↑ approachability Palmstierna et al. (2008) Sweden L Temperament 16467 12 months QNW ↑NW at 12 months associated with difficult temperament Bayer, Hiscock, Hampton, and Wake (2007) Australia CS Temperament 692 3–6 months QNW ↑NW at 3–6 months associated with difficult temperament Touchette et al. (2005) Canada L Temperament 1741 5 months Q SD (night) ↓SD (night) at 5 months associated with difficult temperament Scher (2001a) Israel CS Temperament 94 12 months A SD (night), NW, LSP (night), SL (night), SE ↑SE at 12 months associated with ↑fussiness SD (night), NW, LSP (night), and SL (night) at 12 months not associated with fussiness Scher, Tirosh, and Lavie (1998) Israel CS Temperament 30 12 months A SD (night), NW, SE, BT ↑SD (night), ↑NW, ↓SE, and ↓BT at 12 months associated with ↑rhythmicity ↓BT at 12 months associated with positive mood SD, NW, SE, BT at 12 months not associated with other dimensions of temperament Gibson, Gander, et al. (2012) New Zealand CS Sleep problems 52 12 months A SD (24 h, day, night), SL (night), SP (24 h), SE, BT, WT ↓SD (24 h, night) and ↑SP (24 h) at 12 months in infants rated with sleep problems SD (day), SL (night), SE, BT, and WT at 12 months not associated with sleep problems Bayer et al. (2007) Australia CS Sleep problems 692 3–6 months QNW ↑NW at 3–6months associated with maternal report of sleep problem Hiscock and Wake (2001) Australia CS Sleep problems 738 7–9 months Q NW, SP (day), SL, BT, WT ↑NW, ↓SP (day) and ↑SL at 7–9 months in infants reported by mothers as presenting a sleep problem ↑BT and ↓WT marginally associated with maternal reports of sleep problems St James-Roberts and Peachey (2011) UK/ Denmark L Crying 610 233 1 and 3 months QNW ↑NW at 3 months associated with prolonged crying at 1 month in one study but not in another DeLeon and Karraker (2007) USA CS Crying 41 9 months D SD (24 h, day, night), WASO, NW, SP (day) ↓SD (night), ↑WASO, ↑NW at 9 months associated with ↑ daytime crying SD (24 h, day), and SP (day) at 9 months not associated with daytime crying Harrison (2004) UK L Crying 66 1, 2, 3 months D SD (24 h, night) SD (24 h, night) not associated with crying ↓SD (24 h, night) at 1 month, but not at 2 and 3 months associated with ↑evening crying Lee (2000) Korea CS Crying 188 0–4 months D SD (24 h) ↓SD (24 h) at 0–4 months associated with ↑cry duration 16 C. C. DIAS AND B. FIGUEIREDO St James-Roberts, Conroy, and Hurry (1997) UK CS Crying 132 1 month D SD (24 h, day, night), WASO ↓SD (24 h, day) at 1 months in persistent than in moderate criers SD (night) and WASO at 1 month not associated with crying Non-associated factors Agarwal, Gupta, Pushkarna, and Bhargava (2000) India CS Massage and use of oil 125 1 month D SD (24 h, day, night), NW, SP (24 h, day) SD (24 h, day, night), NW and SP (24-h, day) at 1 month not associated with massage and use of oil Johnson, McMahon, and Gibson (2014) Australia L Conception mode 134 7 months D SD (24 h) SD (24 h) at 7 months not associated with conception mode Butler, Moore, and Mindell (2016) USA CS Sleep aid 104 0–11 months Q SD (day, night), NW, SP (day), LSP (night), BT, WT ↑NW at 0–11 months associated with pacifier use and ↑LSP (night) at 0–11 months associated with finger suck ↑SD (day) at 0–11 months associated with non-suck and pacifier use SD (night) and SP (day), BT and WT at 0–11 months not associated with sleep aid Odoi, Andrew, Wong, Yiallourou, and Horne (2014) Australia L Sleep aid 30 0–1, 2–3, 5–6 months PSD (day), SP (day) SD (day) and SP (day) at 0–1, 2–3, and 5–6 months not associated with sleep aid Burnham, Goodlin-Jones, Gaylor, and Anders (2002) USA L Sleep aid 80 1, 3, 6, 9, and 12 months V SD (night), NW, LSP (night) SD (night), NW, and LSP (night) not associated with sleep aid Ball (2007) UK CS Sleep arrangements (twins) 24 1–3months V SD (night), NW SD (night) and NW at 1–3 months not associated with sleep arrangements in twin infants Design: CS Cross-sectional; L Longitudinal. Sleep measures: A Actigraphy; D Diary; EEG Electro encephalography I Interview; MMS Motility Monitor System; NS Not Specified; O Observation; PPolysmonogrpahy; Q Questionnaire; V Video recording. Sleep-wake behaviour: BT Bedtime; LSP Longest sleep period; SL Sleep latency; NW Night wakings; SD Sleep duration; SE Sleep efficiency; SP Sleep periods; WT Wake Time; WASO Wake After Sleep Onset. EARLY CHILD DEVELOPMENT AND CARE 17 Table 2. Factors positively and negatively affected by sleep-wake behaviour during the first 12 months of life. First author Year of publication Country Design Associated factor N Age (months) Sleep measure Sleep-wake behaviour Main result Positive factors McDaniel and Teti (2012) USA L Co-parenting 150 1 and 3 months DNW ↑NW at 1 and 3 months indirectly predicted ↓co-parenting quality Negative factors Tikotzky et al. (2015) Israel L Parental bedtime involvement 57 3 and 6 months Combined measures: A, D, and Q SD (night), NW, SE SD (night), and SE at 3 and 6 months and NW at 3 months not associated with nighttime paternal involvement at 6 months Johnson et al. (2014) Australia L Parental bedtime involvement 134 7 months D SD (24 h) ↓SD (24 h) at 7 months associated with ↑maternal bedtime involvement at 18 months Tikotzky and Shaashua (2012) Israel L Parental bedtime involvement 71 12 months ANW ↑NW at 12 months associated with ↑parental bedtime involvement at 4 years Sharkey et al. (2016) USA L Parental mental health 31 0, 1, and 4 months D SD (24 h), SP (24 h) ↑SP (24 h) at 0 and 1 month associated with ↑maternal depressive symptoms ↓SD (24 h) at 0 and 1 month associated with ↑maternal stressors at 4 months McDaniel and Teti (2012) USA L Parental mental health 150 1 and 3 months DNW ↑NW at 1 and 3 months indirectly predicted ↑maternal depression Klingenberg et al. (2013) Denmark L Physical growth 311 9 months Q SD (24 h, night) SD (24 h, night) at 9 months not associated with adiposity indicators at 36 months Gillman et al. (2008) USA L Physical growth 1100 6and 12 months Q SD (24 h) ↓SD (24 h) at 6 and 12 months associated with ↑risk of overweight at 3 years Dionne et al. (2011) Canada L Mental development 1029 6 months I LSP (day, night) ↑LSP (day) at 6 months associated with ↓language outcome at 18, 30 and 60 months LSP (night) at 6 months not associated with language outcome at 18, 30 and 60 months Bernier, Carlson, Bordeleau, and Carrier (2010) Canada L Mental development 60 12 months D SD (24 h), NW, SE ↑SE at 12 months associated with ↑performance on executive tasks at 26 months (but not at 18 months) SD (24 h) and NW at 12 months not associated performance on executive tasks at 18 and 26 months Bouvette-Turcot et al. (2015) Canada L Social emotional problems 209 6 and 12 months Q SD (24 h) ↓SD (24 h) from 6 to 36 months associated with negative emotionality/behavioural dysregulation at 36 months in infants with 5-HTTLPR allele Sadeh et al. (2015) Israel L Social emotional problems 43 12 months A SD (night), NW, SE ↑NW and ↓SE at 12 months associated with ↑attention regulation and behaviour problems at 3–4 years SD (night) at 12 months not associated with attention regulation and behaviour problems at 3–4 years (Continued) 18 C. C. DIAS AND B. FIGUEIREDO Table 2. Continued. First author Year of publication Country Design Associated factor N Age (months) Sleep measure Sleep-wake behaviour Main result Saenz et al. (2015) USA L Social emotional problems 47 3–4 months A SD (night), SE ↓SD (night) at 3–4 months associated with ↑externalizing problems and autism spectrum disorder behaviors at 18– 24 months in girls SD (night) at 3–4 months not associated with internalizing and dysregulation problems SE 3–4 months not associated with social emotional problems Scott et al. (2013) UK L Social emotional problems 8195 6 months Q SD (night), NW ↓SD (night) at 6 months associated with attention deficit hyperactivity disorder NW at 6 months not associated with attention deficit hyperactivity disorder Bordeleau et al. (2012) Canada L Social emotional problems 55 12 months D SD (24 h, night) SD (24 h, night) at 12 months not associated with externalizing and internalizing symptoms at 4 years Jansen et al. (2011) The Netherlands L Social emotional problems 4782 2 months Q SD (24 h), NW ↑NW at 2 months associated with ↑anxiety and depression at 3 years SD (24 h) at 2 months not associated with anxiety and depression at 3 years Novosad, Freudigman, and Thoman (1999) USA CS Temperament 41 0 and 8 months MMS LSP (24 h) ↑LSP (24 h) at 0 months associated with ↓adaptable temperament at 8 months Hysing et al. (2014) Norway L Sleep problems 55831 6 months Q SD (night), NW ↓SD (night) at 6 months associated with ↓SD (night) at 18 months ↑NW at 6 months associated with ↑NW at 18 months Byars, Yolton, Rausch, Lanphear, and Beebe (2012) USA L Sleep problems 359 6, 12 months Q SD (24 h, day), SL (night), SP (day) ↓SD (24 h), ↑SL (night) at 6 and 12 months associated with ↑sleep problems SD (day) at 6 and 12 months not associated with sleep problems ↓SD (24 h), ↑SL (night) at 6 and 12 months associated with ↓SD (24 h), ↑SL (night) at 24 and 36 months ↑SP (day) at 6 months associated with ↑SP (day) at 12 months, but not at 24 and 36 months Tikotzky and Shaashua (2012) Israel L Sleep problems 71 12 months Combined measures: A, D, and Q NW, SE ↑NW at 12 months associated with ↑NW, ↓SE, and ↓SD (night) at 4 years ↑SE at 12 months associated with ↑NW (measured by Q) at 4 years SE at 12 months not associated with NW (measured by A), SE, and SD (night) at 4 years (Continued) EARLY CHILD DEVELOPMENT AND CARE 19 Table 2. Continued. First author Year of publication Country Design Associated factor N Age (months) Sleep measure Sleep-wake behaviour Main result Palmstierna et al. (2008) Sweden L Sleep problems 16467 12 months QNW ↑NW at 12 months associated with ↑NW at 3 and 5 years and with ↓perceived sleep quality at 12 months, 3 and 5 years Schwichtenberg, Shah, and Poehlmann (2013) USA L Attachment 171 4, 9 months D SD (day, night), NW, SP (day) ↑SD (day) from 4 to 9 months predicted secure attachment at 16 months SD (night) and NW not associated with attachment Beijers, Jansen, RiksenWalraven, and de Weerth (2011) The Netherlands L Attachment 193 0–6 and 12 months DNW ↑NW at 0–6 months associated with insecure-resistant attachment at 12 months ↓NW at 6 months associated with avoidant attachment at 12 months No associations between NW at 12 months and attachment Design: CS Cross-sectional; L Longitudinal. Sleep measures: A Actigraphy; D Diary; EEG Electro encephalography I Interview; MMS Motility Monitor System; NS Not Specified; O Observation; PPolysmonogrpahy; Q Questionnaire; V Video recording. Sleep-wake behaviour: BT Bedtime; LSP Longest sleep period; SL Sleep latency; NW Night wakings; SD Sleep duration; SE Sleep efficiency; SP Sleep periods; WT Wake Time; WASO Wake After Sleep Onset. 20 C. C. DIAS AND B. FIGUEIREDO sleep period (time of the longest sleep episode), bedtime/sleep onset time (hour of sleep start during the night), wake time (waking time in the morning), and sleep efficiency (percentage of sleep during the night from bedtime to wake time). Results Databases search After the elimination of duplicates, 8610 relevant papers were identified in the literature search. The examination of titles and abstracts lead to the exclusion of 8244 non-relevant papers and the remaining 366 papers were examined for inclusion/exclusion criteria. Two hundred and twenty papers met one or more exclusion criteria and were excluded. This systematic review included 146 papers. Figure 1 presents a flow diagram of the search. Articles reviewed Studies performed in 25 countries were included. Most of the studies were performed in the United States (n= 42), Israel (n= 22), UK (n= 15), Australia (n= 11), or Canada (n= 10) and about half of the studies presented a longitudinal design (n= 76). Infant sleep-wake behaviour’s measures included questionnaire (n= 53), diary (n= 33), actigraphy (n= 17), interview (n= 10), video recording (n= 7), polysomnography (n= 5), observation by experimented researchers (n= 2), electroencephalography (n= 1), motility monitoring system (n= 1), combined measures (n= 15; 8 studies used actigraphy and sleep diary; 4 studies used actigraphy and questionnaire; 2 studies used actigraphy, sleep diary and questionnaire; and 1 study used sleep diary and polysomnography), and 2 studies did not specify sleep-wake behaviour measures. About half of the studies were scored as good (n= 76), and the other half as moderate quality (n= 70) in the Quality Index. Factors positively and negatively associated with sleep-wake behaviour The following factors emerged as positively associated with sleep-wake behaviour during the first 12 months of life: being a first-time infant in 4/6 studies, Caucasian ethnicity in 3/3 studies, higher parental educational/health literacy level in 3/5 studies, lower sensory and environmental stimuli in 1/1 study, better genetic/environmental influences in 1/1 study, outdoor environment in 1/1 study, Figure 1 . Search strategy flow chart. EARLY CHILD DEVELOPMENT AND CARE 21 sleeping in prone position in 1/1 study, wearing Ö4 fabric in 1/1 study, regulated cortisol and melatonin levels in 4/4 studies, infant secure attachment patterns in 2/3 studies, and better mother-infant relationship in 3/3 studies (see Table 1). On the other hand, the following factors emerged as negatively associated with sleep-wake behaviour during the first 12 months of life: male gender in 10/12 studies, older maternal age in 2/2 studies, single/divorced parents in 2/2 studies, non-native parents in 1/1 study, lower socio-economic status in 3/5 studies, winter months in 1/1 study, urban environments in 1/1 study, less exposure to light in 1/1 study, and more exposure to maternal smoking in 1/1 study, gestational exposure to smoke, alcohol, substances, namely alcohol, tobacco, cocaine, marijuana, and methamphetamine, and stressful events in 3/4 studies, planned C-section in 1/1 study, and preterm delivery in 4/4 studies, breastfeeding in 22/27 studies, earlier introduction of solids, higher number of feedings, and diet components in 3/4 studies, later bedtimes, less bedtime activities, and television and media exposure in 5/5 studies, more parental bedtime involvement (characterized by parental presence at bedtime, nursing or rocking at bedtime, putting the infant in crib asleep, or feeding back to sleep) in 8/8 studies, bed-sharing or co-sleeping in 10/11 studies, cloth diapers in 1/1 study, maternal depression, stress, or fatigue and family dysfunction and stress in 17/18 studies, worse parental sleep in 7/7 studies, lower parental involvement in 4/5 studies, emergence of crawling in 4/6 studies, weight gain in 3/4 studies, colic in 2/2 studies, health problems in 5/6 studies, lower scores in mental development tasks in 6/7 studies, social and emotional problems in 6/7 studies, difficult temperament in 10/10 studies, sleep problems in 3/3 studies, and crying in 5/5 studies (see Table 1). Massage and use of oil, conception mode, sleep aid, and sleep arrangements in twins were not associated with infant sleep-wake behaviour (see Table 1). Factors positively and negatively affected by sleep-wake behaviour Sleep-wake behaviour during the first 12 months of life was shown to positively affect co-parenting quality in 1/1 study and negatively affect parental bedtime involvement in 2/3 studies, maternal mental health in 2/2 studies, obesity in 1/2 study, performance in mental tasks in 2/2 studies, social emotional problems in 5/6 studies, temperament in 1/1 study, sleep problems in 4/4 studies, and attachment in 2/2 studies (see Table 2). Discussion This study aimed to provide a systematic review of the literature on associated factors with sleepwake behaviour during the first 12 months of life. This systematic review considered different sleep-wake behaviours and included studies performed over the last 20 years in 25 different countries. Factors positively and negatively associated with sleep-wake behaviour The most consistent factors found in literature as being positively associated with the different sleepwake behaviours during the first 12 months of life were: being a first-time infant, Caucasian ethnicity, the regulation of the HPA axis, secure attachment pattern and a positive mother-infant relationship. The other factors were either poorly explored or provided inconsistent results across the different studies. Being a first-time infant was associated with longer sleep duration and less night wakings (Kozyrskyj et al., 2009; Santos et al., 2008; So et al., 2007). Results from studies with the smallest samples either suggested no differences in the different sleep-wake behaviours that were analyzed (Kaley et al., 2012; Quillin, 1997; So et al., 2007) or a tendency for longer sleep duration in non-first-time infants (Kaley et al., 2012). When the number of siblings was assessed, different results were found, namely more night wakings in infants with more siblings in one study (Kozyrskyj et al., 22 C. C. DIAS AND B. FIGUEIREDO 2009) and no differences in another study (Blair et al., 2012). Studies addressing birth order also differed regarding the time of sleep-wake behaviour assessment. While during the first months, results were not consistent (Kaley et al., 2012; Quillin, 1997; So et al., 2007), in the second half of the first year, non-first-time infants were shown to present less sleep duration during the night (So et al., 2007), and more night wakings (Kozyrskyj et al., 2009; Santos et al., 2008). As the most important changes in sleep-wake behaviour occur during the first 3 months (Burnham et al., 2002; Henderson, France, & Blampied, 2011), differences in birth order may not be easily seen in the first months. Caucasian ethnicity was consistently associated with longer sleep duration during the 24-hour period and more night wakings when compared with non-caucasian ethnicity (Blair et al., 2012; Nevarez et al., 2010; Santos et al., 2012). This result is consistent with previous research showing cultural differences in sleep-wake behaviours between Caucasian and Asian infants (Mindell, Sadeh, Wiegand, How, & Goh, 2010). Although some inconsistent results, a secure attachment was associated with more regulated sleep-wake behaviour, characterized by more sleep duration during the night, less night wakings, and a longer longest sleep period in 2 studies (Pennestri et al., 2015; Zentall et al., 2012). This may be explained by the fact that secure infants are more able to deal with the mother separation during the night and rely on mother’s availability, presenting a more regulated sleep-wake behaviour during the night (Zentall et al., 2012). Regarding mother-infant interaction, different results have been found. A positive mother-infant relationship was associated with a higher increase in the longest sleep periods (de Graag et al., 2012) and with more night wakings, but not with sleep duration during the night and bedtime (Scher, 2001b). Researchers studying preterm infants showed the importance of sleep-wake behaviors during the day in association with the mother-infant relationship (Schwichtenberg et al., 2011). Although few studies addressed infant hormonal factors, results suggested a trend for an association between a regulation of the HPA axis and less night wakings (Lucas-Thompson et al., 2009) and more sleep during the night (Lucas-Thompson et al., 2009). Results from a recent study were controversial, however, this study was conducted with infants with colic (Brand et al., 2011), and colic were shown to be associated with infant sleep-wake behaviour in previous research (Kirjavainen et al., 2001; White et al., 2000). Furthermore, lower morning melatonin levels were also associated with increased sleep duration during the night in one study (Shinohara & Kodama, 2011). The most consistent factors negatively associated with different sleep-wake behaviours during the first 12 months of life were: male gender, breastfeeding, bedtime routines, bed-sharing, parental mental health, parental sleep, and infant social-emotional and sleep problems. Other factors were also negatively associated with sleep-wake behaviour, namely lower socio-economic status, preterm birth, crawling onset, difficult temperament, and crying. However, considering the paucity of studies or the inconsistent results, more research is needed. Male gender was consistently associated with shorter sleep duration, more night wakings, less sleep efficiency, and shorter longest sleep periods during the first 12 months of life. Interestingly, results from studies performed in Australia suggested no gender differences in the different sleepwake behaviours that were analyzed (Kozyrskyj et al., 2009; So et al., 2007), which can underlie some cultural characteristics. Non-Australian studies, whose results showed no gender differences in the different infant sleep-wake behaviours, were conducted with small samples and most of them assessed age ranges rather than specific ages (Goodlin-Jones et al., 2001; Kaley et al., 2012; Lampl & Johnson, 2011; Saenz et al., 2015; Thomas & Foreman, 2005). Considering that infant sleep-wake behaviour during the first months is marked by both individual and developmental changes (Figueiredo et al., 2016), the use of small sample sizes or age ranges could difficult the assessment of gender differences (Weinraub et al., 2012). Breastfeeding was consistently associated with more night wakings (Anuntaseree et al., 2008; Ball, 2003; DeLeon & Karraker, 2007; Engler et al., 2012; Galbally et al., 2013; Huang et al., 2016; Hughes et al., 2015; Hysing et al., 2014; Kaley et al., 2012; Kozyrskyj et al., 2009; Mindell et al., 2009,2012; Ramamurthy et al., 2012; Schwichtenberg & Poehlmann, 2009; Tikotzky et al., 2015; Wolke et al., 1998). This EARLY CHILD DEVELOPMENT AND CARE 23 is congruent with previous literature showing that the quick digestion of breast milk could lead to a more fragmented sleep in breastfed infants (Burness, 1979). However, it is not clear the association between feeding method and other sleep-wake behaviours, namely sleep duration, sleep periods or longest sleep period (Cubero et al., 2005; DeLeon & Karraker, 2007; Demirci et al., 2012; Engler et al., 2012; Huang et al., 2016; Hughes et al., 2015; Kaley et al., 2012; Lampl & Johnson, 2011; Lee, 2000; Mindell et al., 2012; Morgan et al., 2004; Nevarez et al., 2010; Quillin & Glenn, 2004; Ramamurthy et al., 2012; Schwichtenberg & Poehlmann, 2009; Thomas, 2000). Less arousing activities, no reading, late betimes, no bedtime routine, and television and media exposure before bedtime were associated with shorter sleep duration during the night and more night wakings (Cespedes et al., 2014; Mindell et al., 2009; Nevarez et al., 2010; Philbrook & Teti, 2016; Vijakkhana et al., 2015). This is congruent with findings that show that sleep hygiene is associated with infant sleep-wake behaviour (Mindell et al., 2009). Furthermore, higher parental bedtime involvement, characterized by parental presence at bedtime, nursing or rocking at bedtime, putting the infant in crib asleep, or feeding back to sleep were also associated with shorter sleep duration and longest sleep periods, more sleep latency during the night and more night wakings (Anuntaseree et al., 2008; DeLeon & Karraker, 2007; Goodlin-Jones et al., 2001; Huang et al., 2016; Mindell et al., 2009; Philbrook & Teti, 2016; Ramamurthy et al., 2012; Tikotzky & Sadeh, 2009; Touchette et al., 2005). These findings may be explained within the context of the transactional model that argues that parental behaviours are the most immediate and direct factor influencing infant sleep-wake behaviours (Sadeh et al., 2010). The level of parental involvement at bedtime is crucial to the development of the infant’s abilities of self-soothing and self-regulation (Sadeh et al., 2010). In the presence of a low parental involvement at bedtime, the infant is taught to self-sooth and self-regulate its sleep-wake behaviors, while in the presence of high parental involvement at bedtime, the infant is not able to develop these skills (Sadeh et al., 2010). Sleep arrangements (characterized by bed-sharing or co-sleeping) were consistently associated with shorter sleep duration during the night and more night wakings (Bruni et al., 2014; DeLeon & Karraker, 2007;Guyer et al., 2015; Jenni et al., 2005; Mao et al., 2004; Möllborg et al., 2011; Philbrook & Teti, 2016; Santos et al., 2008; Touchette et al., 2005). Bed-sharing/co-sleeping promotes higher physical contact with the parents and that could interfere with the infant’s ability of self-comforting, causing more difficulties in the ability of the infant to return to sleep after night wakings (Green, Groves, & Tegano, 2004; Morrell & Steele, 2003). Moreover, previous research also showed an association between co-sleeping/bed-sharing and infant’s dysregulation, breastfeeding and putting the infant in bed asleep, arguing that co-sleeping/bed-sharing could be used as a parent’s strategy to deal with the infant’s characteristics and the feeding method (DeLeon & Karraker, 2007). Only 1 study showed no associations between sleep arrangements and infant sleep-wake behaviour (Baddock et al., 2006). However, this study analyzed differences between bed-sharing and cot-sleeping, being cot-sleeping defined as sleeping in a cot, that is usually adjacent to the parent’s bed (Baddock et al., 2006). Furthermore, this study was performed in New Zealand, where the lowest bed-sharing rates were shown (Mindell et al., 2009). No association between sleep arrangements and sleep-wake behaviour, when measured by actigraphy, was found in another study (Volkovich et al., 2015). However, the analyses of this study were controlled for feeding method, which has been shown to be associated with sleep arrangements in previous research (DeLeon & Karraker, 2007). Interestingly, although a recent study, performed in China, found more sleep duration during the night in independent sleeping infants, no association was shown between sleep arrangements and night wakings (Huang et al., 2016). Parental mental health, especially maternal depression and fatigue and family dysfunction and stress have been associated with shorter sleep duration (day, night and 24-hour period) and longest sleep period (night), and more night wakings and WASO (Armitage et al., 2009; Baird et al., 2009; Brand et al., 2014; Dennis & Ross, 2005; Goldberg et al., 2013; Gress-Smith et al., 2012; Hughes et al., 2015; Karraker & Young, 2007; Loutzenhiser et al., 2015; Mao et al., 2011; Nevarez et al., 2010;O’Connor et al., 2007; Piteo et al., 2013; Saenz et al., 2015; Sinai & Tikotzky, 2012; 24 C. C. 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