For the 940 participants, the mean age was 33.0 (SD: 4.7) years, prepregnancy body mass index was 24.3 (SD: 4.7) kg/m2, and 22 percent classified themselves as other than White. Reflective of a generally employed and insured managed-care population, relatively few women had less than a college degree (24 percent) or had annual household incomes below $40,000 (10 percent).
At 1 year postpartum, the mean weight retention was 0.8 (SD: 4.5) kg (range: −17.3 to 25.5), and 124 (13 percent) had SPPWR. The mean for hours of sleep per 24-hour period at 6 months postpartum was 6.7 (SD: 1.2) hours/day. Sleep duration categories were distributed as follows: ≤5 hours/day (n = 114, 12 percent); 6 hours/day (n = 280, 30 percent); 7 hours/day (n = 321, 34 percent); and ≥ 8 hours/day (n = 225, 24 percent). Women across sleep categories had similar gestational weight gains (15 kg), but those who slept ≤5 hours/ day had a slightly higher mean prepregnancy body mass index (25 vs. 24 kg/m2) and were more likely to be multiparous than women who slept ≥7 hours/day (data not shown).
The mean for hours of sleep per 24-hour period at 1 year postpartum was 7.0 (SD: 1.1) hours/day. More women reported longer sleep durations at 1 year than at 6 months postpartum with fewer women, 45 (5 percent) and 256 (27 percent) reporting ≤5 hours/day or 6 hours/day, respectively, and greater proportions, 356 (38 percent) and 283 (30 percent) reporting 7 hours/day or ≥8 hours/day, respectively.
Among 786 women, the net weight loss averaged 2 kg per month for the first 6 months and 0.3 kg per month for the subsequent 6 months postpartum, with a similar trajectory of weight loss among prepregnancy body mass index groups. The mean weight loss from 6 months to 1 year postpartum was −1.5 (SD: 3.0) kg in normal weight and −1.9 (SD: 4.7) kg in overweight women. The mean weight loss between 6 months and 1 year postpartum was lower with shorter sleep duration: −1.2 (SD: 3.2) kg for ≤5 hours/day, −1.7 (SD: 3.5) kg for 6 hours/day, −1.5 (SD: 3.4) kg for 7 hours/day, and −1.8 (SD: 3.7) kg for ≥8 hours/day.
The mean for 1-year postpartum weight retention across categories of sleep duration at 6 months postpartum () shows a J-shaped relation, with a mean of 1.6 (95 percent confidence interval (CI): 0.7, 2.5) kg for ≤5 hours/day, 0.3 (95 percent CI: −0.2, 0.8) kg for 6 hours/day, 0.8 (95 percent CI: 0.3, 1.3) kg for 7 hours/day, and 1.0 (95 percent CI: 0.4, 1.7) kg for ≥8 hours/day. In unadjusted logistic models (), shorter sleep duration (≤5 hours/day vs. 7 hours/ day) at 6 months postpartum (odds ratio (OR) 3.08, 95 percent CI: 1.76, 5.38) and at 1 year postpartum (OR = 3.38, 95 percent CI: 1.66, 6.86) and a reduction in sleep duration from 6 months to 1 year postpartum (for decrease vs. no change: OR = 1.94, 95 percent CI: 1.19, 3.17) were each directly associated with SPPWR. The perception of sleep adequacy was not associated with SPPWR.
Mean (95% confidence interval) postpartum weight retention for categories of sleep duration at 6 months postpartum, Project Viva, 1999–2003.
Frequencies and unadjusted associations of sleep duration characteristics with substantial postpartum weight retention at 1 year postpartum, Project Viva, 1999–2003
shows the maternal sociodemographic and prenatal characteristics examined as potential confounders of the sleep and SPPWR association. The characteristics, in order of magnitude of their direct associations with SPPWR, were age less than 25 years, single status, less education, lower household income, non-White race/ethnicity, excessive gestational weight gain, gestational hypertension, obesity before pregnancy, and multiparity.
Frequencies and unadjusted associations of maternal and infant characteristics with substantial postpartum weight retention at 1 year postpartum, Project Viva, 1999–2003
The maternal characteristics at 6 months postpartum most strongly associated with SPPWR in unadjusted analyses () included higher physical inactivity (television/ video viewing), consuming lower levels of dietary fiber, dieting intentionally, shorter duration of exclusive breastfeeding, and postpartum depression. Women with a shorter duration of any breastfeeding through 1 year postpartum were twice as likely to have SPPWR.
Frequencies and unadjusted associations of maternal postpartum behaviors with substantial postpartum weight retention at 1 year postpartum, Project Viva, 1999–2003
In multivariable models (), we examined the association of sleep duration at 6 months postpartum and SPPWR after taking into account maternal sociodemographic, prenatal, and behavioral attributes. The sociodemographic and prenatal attributes moderately confounded the crude odds ratio for <5 hours/day of sleep and SPPWR (un-adjusted OR = 3.08 vs. ORs = 2.24 and 2.20, respectively, from models 1 and 2). In model 3, the adjusted odds ratio for sleeping ≤5 hours/day versus 7 hours/day was strengthened from 2.20 to 2.32 (95 percent CI: 1.14, 4.71) with the addition of postpartum behaviors (breastfeeding at 1 year, dietary fiber intake, physical inactivity). The crude association of ≥8 hours/day of sleep with SPPWR was abolished with adjustment for potential confounders (models 1, 2, and 3). In model 4, the addition of change in sleep duration between 6 months and 1 year postpartum strengthened the association between shorter sleep duration (≤5 hours/day vs. 7 hours/ day) at 6 months postpartum and SPPWR (OR 3.13, 95 percent CI 1.42, 6.94) with little influence on the other sleep duration category estimates. A direct association with SPPWR was also observed for a decrease in sleep between 6 months and 1 year postpartum (OR 2.05, 95 percent CI: 1.11, 3.78) versus no change in hours/day of sleep duration adjusted for covariables.
TABLE 4 Unadjusted and multivariable-adjusted odds ratios of substantial postpartum weight retention at 1 year postpartum according to categories of maternal sleep duration at 6 months and change in sleep duration from 6 to 12 months postpartum, Project Viva, (more ...)