Sleep Medicine 14 (2013) 1092–1099

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Sleep Medicine

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Original Article

Ethnic differences in prevalence and determinants of mother–childbed-sharing in early childhood

1389-9457/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.sleep.2013.04.019

⇑ Corresponding author at: School of Pedagogical and Educational Sciences,Erasmus University Rotterdam, P.O. Box 1738, 3000 DR Rotterdam, The Nether-lands. Tel.: +31 (0) 10 4081712; fax: +31 (0) 10 4089103.

E-mail address: luijk@fsw.eur.nl (M.P.C.M. Luijk).

Maartje P.C.M. Luijk a,b,c,⇑, Viara R. Mileva-Seitz a,c, Pauline W. Jansen b,c, Marinus H. van IJzendoorn a,d,Vincent W.V. Jaddoe c,e,f, Hein Raat g, Albert Hofman e, Frank C. Verhulst b, Henning Tiemeier b,e,h

a School of Pedagogical and Educational Sciences, Erasmus University Rotterdam, P.O. Box 1738, 3000 DR Rotterdam, The Netherlandsb Department of Child & Adolescent Psychiatry and Psychology, Erasmus University Medical Center, P.O. Box 2060, 3000 CB Rotterdam, The Netherlandsc The Generation R Study Group, Erasmus University Medical Center, P.O. Box 2040, 3000 CA Rotterdam, The Netherlandsd Center for Child and Family Studies, Leiden University, P.O. Box 9555, 2300 RB Leiden, The Netherlandse Department of Epidemiology, Erasmus University Medical Center, P.O. Box 2040, 3000 CA Rotterdam, The Netherlandsf Department of Pediatrics, Erasmus University Medical Center, P.O. Box 2060, 3000 CB Rotterdam, The Netherlandsg Department of Public Health, Erasmus University Medical Center, P.O. Box 2040, 3000 CA Rotterdam, The Netherlandsh Department of Psychiatry, Erasmus University Medical Center, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands

a r t i c l e i n f o

Article history:Received 30 January 2013Received in revised form 5 April 2013Accepted 6 April 2013Available online 30 August 2013

Keywords:Bed-sharingFrequencyDeterminantsEthnicityMotherInfant

a b s t r a c t

Background: To date few studies have examined how multiple layers of influences shape the emergenceof bed-sharing practices in the first 2 years postpartum. In our report, we examined bed-sharing in a largemultiethnic sample, exploring the influences of three broad classes of influence on bed-sharing at singletime points and across time: (1) sociodemographic and (2) contextual factors such as breastfeeding,maternal mental health and stress, and (3) child temperament and sleep habits.Methods: Frequencies of bed-sharing were assessed at two time points, 2 and 24 months, in a population-based multiethnic (Dutch, Turkish or Moroccan, and Caribbean) sample of 6309 children born in theNetherlands.Results: In Dutch mothers, the majority of mothers did not share their beds with their child, and bed-sharing rates decreased from 2 to 24 months. Other ethnic groups showed higher bed-sharing rates, typ-ified by both increases in bed-sharing (the Turkish and Moroccan group) and persistence of bed-sharingover time (the Caribbean group). There were few family and child characteristics associated with bed-sharing in the non-Dutch ethnic groups. In contrast, bed-sharing in Dutch mothers was associated withchild temperament and sleeping problems, maternal depression, and sociodemographic variables likecrowding and maternal education.Conclusions: Our results suggest that mothers with a Turkish and Moroccan or Caribbean backgroundwere more influenced by cultural values, whereas bed-sharing practices were more reactive in the Dutchgroup.

� 2013 Elsevier B.V. All rights reserved.

1. Introduction

Bed-sharing, the sharing of a sleeping surface by parents andchildren, is a sleeping strategy with wide inter- and intraculturalvariations in frequency. It has been the predominant sleepingstrategy throughout human evolution [1]. In modern societies,the practice is less common due to a mixture of cultural factors(e.g., parents’ and professionals’ beliefs that bed-sharing compro-mises partner intimacy and early childhood autonomy [2–4]),and medical recommendations (e.g., based on epidemiologic

studies showing potential links between bed-sharing and suddeninfant death syndrome [5]). The primary research focus continuesto be on exploring potential risks for bed-sharing [5,6], with a nar-rower and parallel focus on normative descriptions of bed-sharingthrough observational and laboratory studies [7–10]. In our report,we examined bed-sharing in a large multiethnic sample, exploringthree broad classes of influence on bed-sharing at single timepoints and across time: (1) sociodemographic and (2) contextualfactors such as breastfeeding, maternal mental health and stress,and (3) child temperament and sleep habits.

Bed-sharing prevalence is higher in non-Western cultures[11,12]. In 2001 the International Child Care Practices Study re-ported bed-sharing prevalence across 21 countries with frequen-cies ranging between 2% and 88% [13], and similar cross-culturalvariation has been reported in other studies [14–18]. In some

M.P.C.M. Luijk et al. / Sleep Medicine 14 (2013) 1092–1099 1093

Western and typically nonbed-sharing nations, there have been in-creases in bed-sharing over the recent decades; there was an in-crease from 6% to 13% between 1993 and 2000 in the UnitedStates [19], and similar increases were found in Northern Europeancountries such as the Netherlands and Norway [20–23]. Theauthors suggested that this increase could have resulted fromgreater attention to the importance of infant sleep environmentand breastfeeding. Because of this cultural variability, valid bed-sharing prevalence rates are difficult to establish and must be ex-plored in multiple diverse samples.

Bed-sharing prevalence rates do not reveal the underlying influ-ences on this sleeping practice. Among the most widely reportedfactors associated with a greater prevalence of bed-sharing aresocioeconomic factors like lower family income, lower maternalage, lower maternal education, and nonwhite ethnicity [18]. Forexample, the US and UK literature suggests that bed-sharing ratesare greater in nonwhite ethnicities [19,24,25]. Furthermore, thereis evidence that ethnicity has a greater influence on bed-sharingthan SES factors [26]. In general bed-sharing appears to be less pre-valent in cultures that value autonomy and individualism as is thecase for most Western or developed nations, potentially due to par-ents’ desire to instill early independence in their children byencouraging sleeping alone.

Another major maternal component in bed-sharing is breast-feeding; bed-sharing and breastfeeding are positively related[9,27,28]. This component may be a bidirectional and mutuallyreinforcing relationship [29], with bed-sharing both facilitatingbreastfeeding and being facilitated by a mother’s desire to continuebreastfeeding while minimizing the sleep deprivation imposed byfrequent night awakenings [30]. Parental variables such as parentalstress and mental health also are likely to influence bed-sharing.Maternal mental health and particularly depression is an importantdeterminant of maternal care including sleep-related parentingbehavior [31]. Depressed mothers generally are less responsiveand sensitive to their children, report more frequent sleep problemsin their children, and exhibit greater rates of bed-sharing [31–33].There is evidence that the relationship between depression andbed-sharing may be dependent on ethnicity. Maternal depressionis associated with increased bed-sharing for black mothers, butnot for white mothers in the United States [26] and mothers in Bar-bados [34]. Depression imposes considerable burdens not only onthe parent but on entire family units and may be correlated withparental stress [31,32]. Cortesi et al. [35] reported that parents of5- to 9-year-old children who share a bed have significantly greaterlevels of psychologic and marital stress. However, this cross-sec-tional clinical study did not determine if parental stress resultedfrom bed-sharing, or vice versa, or if the results could be general-ized to younger children. Studying these factors in a prospectivelongitudinal cohort study would help to clarify the associations.

As children grow, they become more active contributors toshaping parental care practices [36]. Therefore, child variablesmay influence whether or not parents decide to bed-share and ifthis practice is maintained over time. Two potential child factorsare temperament and sleep problems. Sleep problems and bed-sharing are associated in studies of older children, but the directionor causality is difficult to determine [35,37]; the studies also tendto be cross-sectional in nature, only examining single time points.Further, predictors normally do not include multiple child andmother variables, even when multiple time points were examined[38,39]. To a greater extent, prolonged bed-sharing occurs in fam-ilies with preexisting and persisting child sleep problems [40], sug-gesting that child factors may evoke bed-sharing. In short bed-sharing practices result from multiple interacting factors that playa role in culturally specific ways. Accordingly, attempts to clarifythe multiple predictors of bed-sharing ought to examine multiplesociodemographic, maternal, and child variables.

In our study, frequencies of bed-sharing were assessed at twotime points, 2 and 24 months, in a population-based multiethnic(Dutch, Turkish and Moroccan, and Caribbean) sample of 6309children. We tested the following hypotheses: (1) that prevalencerates would be lower in the Dutch group compared with the Turk-ish and Moroccan and Caribbean groups at both time points and (2)that the major determinants of bed-sharing at both time pointswill differ across ethnicities, so that the odds of bed-sharing inTurkish and Moroccan and Caribbean families may be more influ-enced by cultural factors and less influenced by specific maternaland child characteristics compared to the Dutch families. As a sec-ondary analysis, we examined the maintenance of bed-sharingfrom 2 to 24 months postpartum.

2. Methods

2.1. Study design and participants

Our research is embedded in the Generation R Study, a prospec-tive cohort in Rotterdam, the Netherlands, following children fromthe prenatal period onwards [41]. All pregnant women living inRotterdam and with expected delivery dates of April 2002–January2006 were invited by their midwife or obstetrician to participateduring routine prenatal visits. The estimated rate of participationwas 61%. The research was approved by the Medical Ethical Com-mittee of the Erasmus Medical Center, Rotterdam. All participantssigned written consent. Data on bed-sharing practices were avail-able for 5095 mothers at 2 months and 5361 mothers at24 months.

2.2. Measures

Data for our study were retrieved from medical records andwere collected by prenatal and postnatal questionnaires. On re-quest (i.e., in the case of illiteracy or low education), trained re-search assistants with varied ethnic backgrounds helped with thecompletion of the questionnaires.

2.2.1. Bed-sharingWe assessed sleeping practices at 2 and 24 months using a

parental questionnaire relating to the place of sleep of the child[42]. Bed-sharing was defined as the child sharing a bed with themother or both parents. At 2 months the question was, ‘‘how oftendoes your child sleep in the bed of the parents for a part of thenight or the whole night?’’ More than three times a week was con-sidered bed-sharing. At 24 months the questions was, ‘‘where doesyour child stay for the majority of the night?’’ The options were inthe child’s own bed or in the parents’ bed.

2.2.2. Maternal predictors2.2.2.1. Ethnicity. Maternal ethnic background was determined bythe country of birth of the mother and the mother’s parents, a clas-sification employed by Statistics Netherlands [43]. If the mother orone of her parents was born outside the Netherlands, this countryof birth determined the ethnic background. If both parents wereborn outside the Netherlands, the country of birth of the mother’smother determined the ethnic background. The major ethnicgroups in our study population were Dutch (Northern European,N = 3680; 58%), Turkish and Moroccan (N = 697; 11%), Caribbean(Antillean and Surinamese, N = 539; 9%), and other (all non-Dutchethnicities which did not fall in the previous categories, includingCape Verdean, Indonesian, and multiple black ethnicities[N = 1393; 22%]). Because of the great ethnic heterogeneity of thissample, no additional results except prevalence are presented forthis last group. The Turkish and Moroccan, Antillean, and Surinam-

1094 M.P.C.M. Luijk et al. / Sleep Medicine 14 (2013) 1092–1099

ese groups represented the major non-Western immigrant groupsin the Netherlands [44]. The ethnic groups used in our study werebased on similar cultural background and prevented low cellcounts. This classification has been used in previous studies onthe same sample [45].

2.2.2.2. Breastfeeding. Breastfeeding status was assessed at2 months postpartum through a questionnaire [45], asking ‘‘Doyou breastfeed your child?’’ This included any breastfeeding at2 months of age.

2.2.2.3. Maternal depressive symptoms. Information about maternaldepressive symptoms was obtained by questionnaire at 2 monthspostpartum using the depression scale of the Brief Symptom Inven-tory (BSI), a validated 53-item self-report measure widely used toassess psychologic distress [46]. Subjects ranked items on a 5-pointscale of agreement, from 0 (not at all) to 4 (very much), based onhow much they were troubled by each of the physical or emotionalproblems during the last week. Six items comprised the depressiondimension (e.g., Thoughts of ending your life, Feeling lonely,among others). The BSI has good psychometric properties [47],and the depression scale of the BSI had good internal consistency(a = .85).

2.2.2.4. Maternal confidence. At 2 months postpartum, mothersfilled out the Mother and Baby Scales (MABS; [48]), a 36-itemmother-report assessing maternal confidence and neonatal behav-ior by rating her agreement with a 6-point scale from 1 (does notapply at all) to 6 (applies totally). Thirteen items in the MABS scale(e.g., ‘‘I feel very insecure when my child cries,’’ ‘‘I feel awkwardlooking after my child,’’ among others) comprised the lack of con-fidence in caregiving dimension, with a good internal consistency(a = .82) in our study.

2.2.2.5. Parental stress. We assessed the level of stress in the par-ent–child pair with the Nijmeegse Ouderlijke Stress Index-Kort(NOSIK; [49]), the Dutch version of the Parenting Stress Index-Short Form (PSI-SF; [50]). The NOSIK is a 25-item questionnaireassessing parenting stress related to both parent factors and childfactors. According to published protocols [51], we only used the 11items of the parent domain (e.g., ‘‘Parenthood of this child is harderthan I thought,’’ ‘‘I often do not understand my child,’’ among oth-ers). Weighted sum scores were derived according to the manual[49]. Higher scores indicated higher levels of stress. Reliabilityand validity of the NOSIK are satisfactory [49] and internal consis-tency of the NOSIK was adequate (a = .71).

2.2.3. Child predictors2.2.3.1. Neonatal behavior. We assessed two dimensions of neona-tal behavior through the MABS questionnaire (also used for deriv-ing maternal confidence; see above [48]): unsettled-irregularbehavior and alertness–responsiveness. The unsettled-irregularbehavior dimension was comprised of 15 items assessing irritablebehavior during feeds and in between feeds (e.g., ‘‘My child wasvery restless before he or she settled down,’’ ‘‘My child’s sleepingand waking periods in the last 24 h were disturbed by hiccupsand burping,’’ and ‘‘Sometimes it was difficult and at other timeseasy to calm down my child.’’). This dimension had good internalconsistency in our study (a = .76). The alertness–responsivenessdimension is comprised of eight items (e.g., ‘‘My child is very alertand attentive,’’ ‘‘When I talk to my child, he/she seems to notice,’’among others) with a = .64.

2.2.3.2. Sleep problems. Child sleep problems were assessed at 2and 18 months. At 2 months, parents indicated the number ofawakenings per night [42]. At 18 months, sleep problems were

assessed using the 7-item sleep problems scale of the Child Behav-ior Checklist for toddlers (CBCL) [52]. Internal consistency of thescale was a = .73. The CBCL is a widely used parent-report describ-ing children’s behavior in the previous 2 months. Items are scoredas 0 (not true), 1 (somewhat or sometimes true), or 2 (very true orvery often true). CBCL scores comprised of 7 empirically based syn-drome scales: emotionally reactive, anxious/depressed, somaticcomplaints, withdrawn, sleep problems, attention problems, andaggressive behavior [52].

2.2.3.3. Anxiety symptoms. We assessed child anxiety symptoms at18 months with the CBCL [52]. For the present report, we used the8-item anxious/depressed scale as a predictor of bed-sharing prac-tices. This scale had an internal consistency of a = .57 in our study.

2.3. Covariates

We used several covariates (indicated below) in the model asconfounders, based on evidence that they may affect bed-sharing.We obtained information on maternal age, child gender, parity,and gestational age from records completed by community mid-wives and obstetricians. Maternal educational level was definedby the highest attained education and categorized as low (typicallycorresponding to 612 years of education), medium (13–15 years ofeducation), and high (P16 years of education), following the Sta-tistics Netherlands (2004) guidelines [53]. Marital status was de-fined as married or cohabiting vs having no partner. Crowdingwas a measure of the total number of people with whom themother cohabits.

2.4. Statistical analysis

2.4.1. Incidence and determinants of bed-sharingIn two separate binary logistic regression analyses, we explored

the predictors of bed-sharing at 2 months and at 24 months com-pared with no bed-sharing at 2 months and 24 months, respec-tively (reference groups). We entered three blocks of variablesfor the 2-month bed-sharing analyses (covariates, maternal predic-tors, and child predictors at 2 months), and four blocks at24 months (covariates, maternal predictors, child predictors at2 months, and child predictors at 18 months). Next the resultswere stratified for ethnicity.

2.4.2. Bed-sharing patternsIn a secondary analysis using the same set of determinants, we

performed multinomial logistic regression analyses to calculate theodds of belonging to one of three bed-sharing pattern groups rela-tive to a nonbed-sharing group. The outcome measure, bed-sharingpattern, included the following categories: (1) nonbed-sharers re-ported that their children spent the majority of the night in theirown bed (reference group); (2) early-only bed-sharers reportedbed-sharing at 2 months but not at 24 months; (3) late-onsetbed-sharers reported bed-sharing at 24 months but not at2 months; and (4) persistent bed-sharers reported bed-sharing atboth 2 and 24 months. The four groups were mutually exclusive.

2.4.3. Multiple imputationWe imputed missing data for all the predictor variables in our

model [54]. Missing data ranged between 0% and 11% across vari-ables. All predictors and the outcome were used as predictors inthe multiple imputation models. The outcome was not imputed.The presented data are pooled estimates from 10 imputed datasets.

2.4.4. Nonresponse analysisChildren with missing data on one of the assessments of sleep-

ing practices (n = 1584) were compared with children for whom

M.P.C.M. Luijk et al. / Sleep Medicine 14 (2013) 1092–1099 1095

these data were available (n = 6309). Data more frequently weremissing in mothers who were non-Dutch (P < .001), younger(P < .001), of lower education (P < .001), single parents (P < .001),not breastfeeding (P < .001), and reported more parenting stress(P < .001).

3. Results

3.1. Incidence of bed-sharing

At age 2 months, 1149 (23%) of the 5095 mothers who reportedon bed-sharing practices were bed-sharers. At age 24 months, 620(12%) of the 5361 mothers who reported on bed-sharing practiceswere bed-sharers. Characteristics of the mothers and children forwhom bed-sharing data were available are presented in Table 1.In the ethnicity-stratified analyses, we found differences in the fre-quencies of bed-sharing at 2 and 24 months. At 2 months, mothersfrom Dutch or Turkish and Moroccan descent had comparable ratesof bed-sharing (17% and 16%, respectively), whereas almost half(48%) of Caribbean mothers shared a bed with their child. In thegroup with several other ethnicities combined, the prevalencewas 29%. At 24 months, Dutch mothers decreased to a 5% bed-shar-ing rate, while Turkish and Moroccan mothers increased to 20%.Rates in Caribbean mothers decreased to 36%. Within the Turkishand Moroccan group, bed-sharing frequencies were similar andthe frequency was 18% in the group with other ethnicities.

3.2. Determinants of bed-sharing

We found differences between ethnicities in the major predic-tors of bed-sharing. Correlations between study variables can befound in the Supplementary material (Table S1). At 2 months,number of infant awakenings at night was the only factor signifi-cantly associated with greater bed-sharing odds for all ethnicities.

Table 1Sample characteristics.

Dutch(n = 3680)

Turkish andMoroccan (n = 697)

Caribbean(n = 539)

EducationHigh 63.5 14.7 21.8Medium 25.3 34.0 45.6Low 11.2 51.4 32.6

Marital status, single 5.5 5.1 37.1Parity, multiparous 42.6 56.5 41.7Gestational age at

birth39.8 (1.8) 40.0 (1.7) 39.5 (1.8)

Child gender, girl 49.6 48.8 48.6Crowding 2.49 (0.8) 3.15 (1.3) 2.58 (1.0)Bed sharing at 2 mo 17.4 16.3 48.4Bed sharing at 24 mo 5.4 19.8 35.9

Maternal factors at 2 moMaternal age 31.9 (4.2) 28.2 (5.1) 28.6 (5.9)Breastfeeding at 2 mo 67.2 68.0 59.0Maternal depressive

symptoms0.15 (0.34) 0.46 (0.71) 0.30 (0.58)

Lack of confidence incaretaking

14.98 (10.87) 14.97 (11.14) 13.03 (10.57)

Child factors at 2 moAwakenings per night 1.69 (0.58) 1.86 (0.56) 1.80 (0.60)Unsettled-irregular 28.33 (13.02) 26.79 (13.95) 25.93 (13.47)Alertness–

responsiveness32.18 (5.29) 31.95 (5.64) 33.66 (5.50)

Factors at 18 moAnxiety symptoms 0.88 (1.09) 2.21 (1.96) 1.45 (1.55)Sleep problems 1.57 (1.98) 2.94 (2.63) 2.56 (2.49)Parenting stress 0.27 (0.26) 0.48 (0.43) 0.31 (0.31)

Abbreviation: mo, months.Values are percents or means (standard deviation).

Breastfeeding was associated with greater odds of bed-sharing forDutch or Turkish and Moroccan mothers. Being a single motherwas associated with greater likelihood to bed-share in the Dutchgroup. Lower maternal education was significantly associated withlower odds for bed-sharing in the Turkish and Moroccan group. As-pects of infant temperament were associated with greater odds forbed-sharing in two of the ethnic groups. In Dutch mothers, moreunsettled-irregular behavior was associated with greater bed-shar-ing odds, and alertness–responsiveness was associated with great-er bed-sharing odds in Turkish and Moroccan mothers. Crowdingand having more than one child was associated with greater oddsof bed-sharing in Dutch mothers (Table 2).

More child sleep problems as reported at 18 months and thepresence of bed-sharing at 2 months significantly predicted greaterodds of bed-sharing at 24 months for Dutch and Caribbean groups.Higher maternal age and depression scores were significantly asso-ciated with greater bed-sharing odds at 24 months in Dutch moth-ers. Having more than one child was associated with greater oddsof bed-sharing in Caribbean mothers. None of the factors wereassociated with greater odds of bed-sharing for Turkish and Moroc-can mothers. Findings at 2 and 24 months were similar within theTurkish and Moroccan group; results for the Turkish and Moroccanmothers are presented in the Supplementary material (S2).

3.3. Bed-sharing patterns

Next we classified all mothers as belonging to one of four sleepingpatterns. The classifications were as follows: 3062 were non-bed-sharers, 671 mothers were early-only bed-sharers (i.e., bed-sharingat 2 months but not 24 months), 215 mothers were late-onset bed-sharers (i.e., bed-sharing only at 24 months), and 199 mothers werepersistent bed-sharers (i.e., bed-sharing at both 2 and 24 months).Ethnicity was a major predictor of all three bed-sharing patternswith the greatest odds found for persistent bed-sharing Caribbeanmothers (Table 3). Single parenthood also was associated with allpatterns. Lower education was associated with greater odds of per-sistent and late-onset bed-sharing but not with early-only bed-shar-ing. Of the maternal and child variables, breastfeeding and a highernumber of infant awakenings at 2 months were associated withgreater odds in both of the bed-sharing groups, consisting of earlybed-sharing: early-only and persistent. Greater child sleep problemsat 18 months were found for all bed-sharing patterns, and child anx-iety problems at 18 months were associated with lower odds forearly-only bed-sharing. Ethnic stratification of the patterns wasnot possible due to subsequent low cell counts.

4. Discussion

In our large, multiethnic, prospective study, we showed that theprevalence of bed-sharing practices differs across cultural back-grounds; the majority of mothers did not share their beds withtheir child, with decreasing rates in the first 2 years of life in Dutchmothers. Other ethnic groups (Turkish or Moroccan and Caribbean)showed higher bed-sharing rates, increases in bed-sharing prac-tices, and persistence of bed-sharing over time. Our results also re-vealed a larger role for familial influences on bed-sharing in Dutchmothers. In contrast, we showed that Turkish or Moroccan andCaribbean mothers had few family and child factors associatedwith bed-sharing and may have been more likely influenced bycultural factors instead.

4.1. Incidence of bed-sharing

Almost a quarter of the children in our study (23%) shared a bedwith their parents at the age of 2 months, and this number

Table 2Variables associated with bed-sharing stratified by ethnicity.

Bed-sharing at 2 months Bed-sharing at 24 months

DutchOR (95% CI)

Turkish and MoroccanOR (95% CI)

CaribbeanOR (95% CI)

DutchOR (95% CI)

Turkish and MoroccanOR (95% CI)

CaribbeanOR (95% CI)

N = 527 (17%) N = 83 (16%) N = 206 (48%) N = 181 (5%) N = 103 (20%) N = 139 (36%)

EducationHigh ref ref ref ref ref refMedium 0.94 (0.73–1.21) 0.46 (0.21–0.99) 1.28 (0.74–2.21) 1.38 (0.86–2.22) 2.08 (0.82–5.26) 1.16 (0.53–2.54)Low 0.85 (0.56–1.27) 0.53 (0.25–1.11) 1.17 (0.61–2.22) 3.62 (2.07–6.35) 1.31 (0.51–3.63) 1.21 (0.48–3.04)Marital status, single 3.06 (1.99–4.70) 1.44 (0.42–4.94) 1.19 (0.74–1.91) 1.97 (0.99–3.92) 1.03 (0.23–4.66) 1.71 (0.83–3.55)Parity, multiparous 1.51 (1.08–2.12) 1.22 (0.62–2.38) 0.98 (0.58–1.66) 0.98 (0.52–1.85) 0.79 (0.35–1.81) 2.41 (1.05–5.56)Gestational age at birth 1.02 (0.96–1.09) 0.90 (0.77–1.05) 0.92 (0.80–1.06) 0.98 (0.88–1.09) 0.93 (0.78–1.10) 1.09 (0.89–1.35)Child gender, girl 0.95 (0.77–1.16) 0.96 (0.58–1.59) 0.73 (0.49–1.10) 1.22 (0.83–1.79) 0.96 (0.53–1.77) 1.19 (0.64–2.20)Crowding 1.25 (1.01–1.54) 1.23 (0.97–1.57) 1.13 (0.88–1.45) 1.23 (0.84–1.80) 1.08 (0.79–1.48) 0.80 (0.54–1.20)Bed sharing at 2 mo – – – 2.71 (1.74–4.20) 1.95 (0.91–4.18) 5.78 (3.01–11.13)

Maternal factors at 2 moMaternal age 0.98 (0.95–1.00) 0.96 (0.91–1.02) 1.00 (0.96–1.04) 1.06 (1.01–1.12) 1.04 (0.98–1.11) 0.96 (0.89–1.02)Breastfeeding at 2 mo 2.03 (1.57–2.62) 2.71 (1.39–5.30) 1.09 (0.71–1.67) 1.07 (0.69–1.67) 0.68 (0.34–1.36) 0.85 (0.44–1.66)Maternal depressive symptoms 1.15 (0.84–1.57) 1.12 (0.76–1.65) 1.47 (0.98–2.18) 1.66 (1.06–2.59) 0.92 (0.59–1.43) 0.68 (0.36–1.30)Lack of confidence in caretaking 0.99 (0.98–1.01) 1.02 (0.99–1.05) 1.01 (0.99–1.04) 1.01 (0.99–1.04) 1.00 (0.96–1.03) 0.99 (0.95–1.03)

Child factors at 2 moAwakenings per night 4.04 (3.29–4.95) 2.33 (1.43–3.78) 2.71 (1.85–3.97) 1.15 (0.81–1.64) 1.03 (0.59–1.83) 1.06 (0.61–1.85)Unsettled-irregular 1.02 (1.01–1.03) 1.01 (0.99–1.03) 0.99 (0.97–1.01) 0.99 (0.97–1.06) 1.01 (0.99–1.04) 0.98 (0.95–1.00)Alertness–responsiveness 0.98 (0.96–1.00) 1.09 (1.03–1.16) 0.99 (0.95–1.04) 1.01 (0.97–1.06) 1.01 (0.95–1.08) 0.97 (0.91–1.03)

Factors at 18 moChild anxiety problems – – – 0.99 (0.84–1.18) 0.98 (0.84–1.14) 1.16 (0.92–1.45)Child sleep problems – – – 1.32 (1.22–1.42) 1.12 (0.99–1.31) 1.28 (1.11–1.49)Parenting stress – – – 0.42 (0.17–1.03) 1.59 (0.72–3.53) 2.62 (0.79–8.71)

Abbreviations: OR, odds ratio; CI, confidence interval; ref, reference group in the regression analyses; mo, months; –, the variable was not included in the 2 month model.Values in bold were considered significant (P < .05).

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decreased to 12% by 24 months. After controlling for multiple con-textual covariates, including maternal age, education, crowdingconditions, parity, and marital status, we showed that ethnicity isa strong predictor of bed-sharing practices. Compared to Dutchmothers, the odds of all bed-sharing patterns were greatest inthe Caribbean group. Our results are congruent with other studiesshowing greater bed-sharing prevalence in nonwhite ethnicities[19,24]. The low rates of early bed-sharing in our Turkish andMoroccan group also have been previously described [13,55]. Weextended these findings by showing that an increase occurs be-tween 2 and 24 months for this subgroup.

Whereas ethnicity may be more influential than SES factors inpredicting bed-sharing prevalence in the United States [26], our re-sults showed persistent effects of SES factors such as maternal edu-cation within some of the ethnic groups and particularly for theDutch. The country of birth of the mother’s mother was used todetermine the ethnic background according to the routinely usedclassification of Statistics Netherlands [42]. The classification doesnot account for differences in cultural shift between first and secondgeneration immigrants, which may have led to an underestimationof the effect of ethnicity. Previously reported bed-sharing preva-lence in the Netherlands ranged from 5% to 13% [20,21,23] but didnot account for differences in ethnicity or child age. All of the previ-ous reports investigated children between the ages of 0–4 months inthe Dutch population. Our study is the first to provide detailed ethnicand age information on the prevalence of this important and increas-ingly common sleep practice in the Netherlands.

4.2. Ethnic differences in determinants of bed-sharing

Consistent with our hypothesis, the Turkish and Moroccan andCaribbean groups had fewer significant bed-sharing predictorscompared with the Dutch group. Moreover, bed-sharing predictorsin the Dutch mothers tended to be negative ones, including moreunsettled-irregular infant behavior, more crowding, single parent-hood (associated with 2-month bed-sharing), and early postpar-

tum maternal depressive symptoms (associated with 24-monthbed-sharing). Thus external factors may influence bed-sharing inthe Dutch group more than in the Turkish and Moroccan andCaribbean groups, potentially because the non-Dutch ethnicitiesare influenced by different and perhaps cultural factors.

This finding supports the idea that bed-sharing is less preva-lent in cultures that place emphasis on the early development ofchildren’s autonomy and individualism, as is the case for most ofthe developed Western nations [11,12]. For Dutch mothers thedecision to share their bed might be a reaction to several envi-ronmental, maternal, and child factors. For example, the Dutchmothers comprised the only group for whom crowding in thehome was a significant predictor. Other studies have reportedno significant associations between crowding and bed-sharingin an inner city population of mostly black or Hispanic mothers[56], congruent with the findings among Turkish or Moroccan,and Caribbean ethnicities in our sample. Furthermore, unset-tled-irregular behavior was associated with bed-sharing at2 months only in Dutch mothers. This finding confirms one smallcross-sectional study which reported more negative tempera-ment in white bed-sharing children [39], suggesting that earlychild temperamental factors might influence bed-sharingpractices.

Moreover, early postpartum depressive symptoms were onlyassociated with bed-sharing at 24 months in Dutch mothers. Wemay hypothesize that late-onset bed-sharing eventually arose asa consequence of lower maternal mood in the early postpartumperiod. The fact that we do not see this significant association inethnicities other than Dutch suggests that mental health inaddition to ongoing contextual factors is more influential for thesleeping practices of Dutch mothers. In a previous study thatexamined maternal mood in relation to bed-sharing, effects wereonly found for black mothers [26]. However, this study populationwas oversampled to contain risk families and the authors reportedlower prevalence of bed-sharing in immigrant mothers, whichquestions the comparability of their findings and ours.

Table 3Variables associated with bed-sharing patterns from 2 to 24 months.

Early-only bed-sharing OR (95% CI) Late-onset bed-sharing OR (95% CI) Persistent bed-sharing OR (95% CI)N = 671 N = 215 N = 199

Ethnicity, Dutch ref ref refTurkish and Moroccan 0.65 (0.43–0.98) 3.34 (2.08–5.37) 1.23 (0.64–2.38)Caribbean 2.35 (1.62–3.40) 3.89 (2.32–6.52) 15.71 (9.74–25.37)Marital status, single 2.61 (1.86–3.65) 2.27 (1.42–3.63) 2.76 (1.72–4.44)

Educational levelHigh ref ref refMedium 0.90 (0.72–1.12) 1.51 (1.05–2.18) 1.60 (1.09–2.36)Low 0.76 (0.55–1.06) 1.83 (1.18–2.84) 1.65 (1.00–2.70)

Parity, multiparous 1.54 (1.18–2.01) 1.12 (0.74–1.68) 1.87 (1.19–2.93)Gestational age at birth 1.00 (0.95–1.06) 0.97 (0.90–1.06) 1.03 (0.93–1.13)Child gender, girl 0.94 (0.79–1.13) 1.24 (0.93–1.67) 0.80 (0.58–1.10)Crowding 1.17 (1.01–1.35) 1.14 (0.94–1.38) 1.11 (0.89–1.39)

Maternal factors at 2 moMaternal age 0.98 (.96–1.01) 1.01 (0.98–1.05) 0.98 (0.95–1.02)Breastfeeding 2 mo, yes 1.77 (1.42–2.21) 0.94 (0.68–1.29) 1.82 (1.25–2.67)Depressive symptoms 1.19 (0.94–1.51) 1.07 (0.79–1.48) 1.11 (0.79–1.57)Lack of confidence in caretaking 1.00 (0.99–1.01) 1.01 (0.99–1.02) 1.01 (0.99–1.03)

Child factors at 2 moAwakenings per night 3.52 (2.95–4.19) 1.20 (0.91–1.57) 4.05 (2.99–5.47)Unsettled-irregular 1.02 (1.01–1.02) 1.00 (0.98–1.01) 1.00 (0.98–1.01)Alertness–responsiveness 1.00 (0.98–1.02) 1.00 (0.97–1.03) 1.00 (0.97–1.04)

Factors at 18 moChild anxiety symptoms 0.92 (0.85–0.99) 0.99 (0.89–1.09) 1.02 (0.91–1.13)Child sleep problems 1.09 (1.05–1.14) 1.28 (1.20–1.37) 1.27 (1.19–1.35)Parenting stress 0.89 (0.63–1.27) 0.90 (0.51–1.59) 1.02 (0.57–1.72)

Abbreviations: OR, odds ratio; CI, confidence interval; mo, months; ref, reference group in the regression analyses.Early-only bed sharing was bed sharing that occurred at 2 months but not at 24 months.Late-onset bed sharing was bed sharing that occurred only at 24 months.Persistent bed sharing was bed sharing that occurred at both 2 and 24 months.Nonbed-sharing was the reference group.Values in bold were considered significant (P < .05).

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Interestingly, breastfeeding at 2 months postpartum was asso-ciated with bed-sharing in the Dutch and Turkish and Moroccangroups but not in the Caribbean group in our study. In a previ-ous study on the same sample, the prevalence of breastfeedingin the Caribbean group was lower than in the Dutch or Turkishand Moroccan groups [45]. The reasons for this apparent dissoci-ation between bed-sharing and breastfeeding in the Caribbeangroup are not clear. There may be different cultural influenceson bed-sharing and breastfeeding. In our report, breastfeedingincluded the range of activities from any breastfeeding to exclu-sive breastfeeding. Further differentiation may be useful in fu-ture studies.

The directionality of the multiple associations between bed-sharing, breastfeeding, maternal mood, and child sleep problemsremains a difficult question to tackle, particularly in the absenceof information about maternal sleep quality. Bed-sharing mothersbreastfeed more [29], and breastfeeding is associated with betterquality maternal sleep [57], and thus with more sleep in bed-shar-ing mothers [58]. Furthermore, bed-sharing is associated withmore positive maternal nighttime experiences and the same totalsleep duration as in solitary sleeping mothers [59,60]. Conversely,mothers scoring higher on depressive symptoms have a tendencyto awaken their nondistressed babies from sleep, sometimes bring-ing them to the parental bed [61]; thus, maternal mood and bed-sharing are interlinked in complex ways. Detailed prospective re-ports of maternal sleep quality during bed-sharing practices couldaid in elucidating the relationship between maternal and childmental health or well-being and sleep.

4.3. Determinants of bed-sharing patterns

Child sleep problems in toddlers were associated with all threebed-sharing patterns. The role of specific sleep-related child

behavior in bed-sharing has been previously studied, but theinterrelations are complex. Some studies have used correlationsas evidence for a causal link between bed-sharing and sleep prob-lems in children [8]. However, others such as Cortesi et al. [35],argue that bed-sharing may be initiated in response to sleepproblems in children, and there is some direct evidence for theevocative effect of child sleep problems on bed-sharing [40].Sleep problems such as night awakenings have a peak at ages4–5 years, and there is a coinciding peak for bed-sharing in thisage range [37] further indicating that the two are related [62].Moreover, parental perceptions of child sleep behaviors and sleepproblems may be more acute in bed-sharing parents [63]. Our re-sults suggest that sleep problems in a young child could makeparents decide to start, stop, or continue to bed-share, possiblyreflecting differing parenting strategies in response to problem-atic sleep. Parenting was indeed found to be one of the few nota-ble predictors in a study on bed-sharing in the United States [64].Parenting practices aside from bed-sharing were not assessed inour study. Parenting stress was included, but this factor wasnot associated with any of the bed-sharing measures indicatingthat parenting practices and parenting stress are related but sep-arate constructs [65].

Child anxiety in toddlers was associated with lower odds of early-only bed-sharing. Thus mothers who rate their children higher onanxious behavior are less often early-only bed-sharers comparedto nonbed-sharing pairs. On the other hand, mothers who onlyshared their beds at 2 months but not at 24 months may have beenless likely to perceive their child as anxious at age of 18 months.Taking the marginal significance of the effect into account, we spec-ulated that the mothers were slightly more uncertain and anxiousthemselves and less often choose to start and subsequently stopbed-sharing. More careful exploration of maternal anxiety pre-and postnatally might help to further elucidate these questions.

1098 M.P.C.M. Luijk et al. / Sleep Medicine 14 (2013) 1092–1099

In a recent study on the impacts of bed-sharing on marital sat-isfaction [66], women were classified according to their intentionto share their bed. The authors only reported less marital satisfac-tion for mothers who were reactive bed-sharers (i.e., who sharedtheir beds in reaction to [perceived] child problems), supportingour suggestion that certain subsamples like our Dutch samplemay share their beds as a reactive strategy. We did not measurethe intent to bed-share in our study; therefore, we could not assessif parents made a conscious decision to bed-share against the cul-tural norms in which they are embedded (e.g., as a positive parent-ing style [30]) or if they bed-shared because solitary sleep was notpossible (e.g., lack of funds for child’s bed, lack of space in the homefor a separate child bed or room). However, we controlled forcrowding of the home and parity, two factors that influenced theamount of space available in the home. Thus our outcomes likelyreflect a voluntary choice of parents to start bed-sharing practices,rather than space constraints. We also did not have informationabout the bed-sharing habits prior to 2 months postpartum andbetween 2 and 24 months. Multiple time point assessments wouldhelp to discern the potentially reactive nature of bed-sharing incertain ethnic groups compared with others. Furthermore, parentsin the study reported how often the child slept in their bed but notfor how many hours per night. This broad measure of bed-sharingfrequencies, together with educational messages against bed-shar-ing in Dutch well-baby clinics, may have resulted in underreport-ing of bed-sharing. Relatedly generalized questions aboutsleeping practices may lead parents to ‘pigeon-hole’ themselvesby choosing a category which may not always apply. Asking multi-ple related questions in different forms (e.g., ‘‘Where did the childsleep last night?’’) may minimize the potential for bias in the re-sponses. Nevertheless, we were able to show that family and eth-nic factors contribute to the shift in bed-sharing practices overtime with two time points.

In the future, it will be important to distinguish between bed-sharing practices that emerge as a consequence of problematicchild behavior or parental experiences and those that emerge sim-ply as a consequence of cultural and sociodemographic constraintssuch as crowding. Untangling these multiple layers of influencecontinues to be a challenge, but we have shown here that bed-sharing appears to be a reactive strategy, influenced by negativecontext, at least for some Dutch mothers. Finally, future researchshould examine the potential child developmental consequencesof bed-sharing practices in ways that account for ethnic and con-textual differences. It is possible to propose that children aredifferentially influenced by reactive parenting strategies, includingbed-sharing in response to external stressors, compared with cul-turally appropriate parenting strategies outside the influence ofnegative context.

Conflict of interest

The ICMJE Uniform Disclosure Form for Potential Conflicts ofInterest associated with this article can be viewed by clicking onthe following link: http://dx.doi.org/10.1016/j.sleep.2013.04.019.

Acknowledgements

The Generation R Study was conducted by the Erasmus MedicalCenter in close collaboration with the School of Law and Faculty ofSocial Sciences of the Erasmus University Rotterdam, the MunicipalHealth Service Rotterdam area, Rotterdam, the Rotterdam Home-care Foundation, Rotterdam, and the Stichting Trombosedienstand Artsenlaboratorium Rijnmond, Rotterdam. We gratefullyacknowledge the contribution of general practitioners, hospitals,

midwives, and pharmacies in Rotterdam. The first phase of theGeneration R Study was made possible by financial support fromthe Erasmus Medical Center Rotterdam, the Erasmus Universityof Rotterdam and the Netherlands Organization for Health Re-search and Development (Zon Mw). Our study was supported byadditional grants from the Netherlands Organization for ScientificResearch; Grant No. 017.106.370 (NWO ZonMW VIDI) to HT, andNWO SPINOZA prize to MHvIJ.

Appendix A. Supplementary data

Supplementary data associated with this article can be found,in the online version, at http://dx.doi.org/10.1016/j.sleep.2013.04.019.

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