Mean (SD) maternal prepregnancy BMI was 24.6 kg/m2 (5.0), and total gestational weight gain was 15.6 kg (5.4). Approximately one-third (29%) of mothers had a prepregnancy BMI > 26.0 kg/m2. According to the 1990 Institute of Medicine recommendations, 51% of women gained excessive weight, 35% gained adequate weight, and 14% gained inadequate weight (). Mean (SD) child BMI z-score was 0.45 units (1.01), and 9% of children were overweight (BMI ≥ 95th percentile for age and sex).
Participant characteristics and their associations with gestational weight gain among 1044 mother-child pairs in Project Viva
On bivariate analysis, gestational weight gain was directly associated with child overweight (OR 1.30, 95% CI: 1.04, 1.62 for each 5 kg). Adjustment for sociodemographic factors, breastfeeding duration, glucose tolerance, and gestation length did not markedly change estimates (), but adjustment for maternal and paternal BMI strengthened the association (OR 1.66, 95% CI: 1.31, 2.12) (). Additional adjustment for fetal growth, which is likely in the pathway between gestational weight gain and child size, slightly attenuated estimates (OR 1.52, 95% CI: 1.19, 1.94). When we instead used BMI < 85th percentile as a reference group, gestational weight gain remained associated with a risk of BMI ≥ 95th percentile (OR 1.44, 94% CI: 1.17, 1.79).
Associations of maternal gestational weight gain with child adiposity-related outcomes at age 3 years, before and after adjustment for potential confounding and pathway variables
Total gestational weight gain was associated with child BMI z-score (0.13 units, 95% CI: 0.08, 0.19 per 5 kg) as well as the sum of subscapular and triceps skinfold thicknesses (0.26 mm, 95% CI: 0.02, 0.51) (), but not with the ratio of subscapular to triceps skinfolds, a measure of truncal obesity (0.003, 95% CI: −0.01, 0.01). The association of net weight gain with child adiposity (0.12 BMI z-score units, 95% CI: 0.07, 0.18, per 5 kg) was similar to that for total weight gain. Additional adjustment for children’s television viewing habits and consumption of fast food and sugar-sweetened beverages did not appreciably alter results (0.13 BMI z-score units, 95% CI: 0.07, 0.19, per 5 kg).
Children of mothers in all Institute of Medicine weight gain groups, even those with inadequate gain, had mean BMI z-scores above the median of the 2000 CDC growth curves,15
which were primarily based upon US children in the 1970s.22
Compared with children exposed to inadequate gestational weight gain, who had an adjusted mean BMI z-score of 0.17 (95% CI: 0.01, 0.33), children exposed to adequate (0.47 units, 95% CI: 0.37, 0.57) or excessive (0.52 units, 95% CI: 0.44, 0.61) gain had higher BMI z-scores (). Women with adequate or excessive gain had approximately a 4-fold increased odds of having an overweight child (odds ratios 3.77, 95% CI: 1.38, 10.27, and 4.35, 95% CI: 1.68, 11.24, respectively), compared with inadequate gain ().
FIGURE Child BMI z-score at age 3 years, according to the maternal gestational weight gain category recommended by the Institute of Medicine1
Adjusted odds* of child outcomes according to Institute of Medicine categories of maternal gestational weight gain
We next performed additional analyses to explore whether observed associations differed by selected maternal and child characteristics. Gestational weight gain was similarly associated with child BMI z-score among children of mothers with prepregnancy BMI 19.8 to 26.0 kg/m2 (0.12 units, 95% CI: 0.04, 0.20 per 5 kg) and BMI >26.0 kg/m2 (0.16 units, 95% CI: 0.06, 0.25 per 5 kg). Accordingly, we saw no evidence for a multiplicative interaction between pre-pregnancy BMI and gestational weight gain (P value = .51). Among the 787 children weighed at age 6 months, additional adjustment for change in weight-for-age z score from birth to 6 months did not diminish the estimated effect of gestational weight gain on child BMI z-score (0.14 units, 95% CI: 0.08, 0.21 per 5 kg). Gestational weight gain remained directly associated with child BMI z-score when we limited the analysis to the 859 mothers with normal glucose tolerance during pregnancy (0.14 units, 95% CI: 0.07, 0.20 per 5 kg) and when we excluded the 67 children born before 37 completed weeks of gestation (0.13, 95% CI: 0.08, 0.19 per 5 kg).
We had blood pressure information for 970 children. Mean (SD) systolic blood pressure was 92.1 mm Hg (10.9). After multivariable adjustment (), systolic blood pressure was an estimated 0.60 mm Hg (95% CI: 0.06, 1.13) higher per 5 kg of gestational weight gain. This effect was partially accounted for by the association of gestational weight gain with child size, a major determinant of blood pressure, and was reduced to 0.34 mm Hg (95% CI: −0.19, 0.87 per 5 kg) after additional adjustment for child BMI.
Because recommendations for gestational weight gain historically have been based on relationships with birth outcomes, we also studied associations with outcomes at birth. Compared with inadequate gain, women with adequate gain did not have a different risk of small or large for gestational age or caesarean birth (). Women with excessive gain had an increased risk of having a large for gestational age baby and a possible reduction in small for gestational age, but no difference in cesarean section rates (). The mean (SD) rate of weight gain after the first trimester was 0.51 (0.18) kg/week. This rate was not associated with risk of preterm birth (adjusted OR 0.98, 95% CI: 0.85, 1.14 per 0.1 kg/wk). Five (19%) of the 27 women with an extremely low rate of gain (de-fined as < 1 kg/month after the first trimester for those with prepregnancy BMI ≤26.0, or <0.5 kg/month for pre-pregnancy BMI > 26.0)1
had preterm births (adjusted OR of preterm birth 3.49, 95% CI: 1.14, 10.67), although none had a small for gestational age infant.