TABLE 3.
Associations of maternal gestational weight gain with birth weight, within sibling groups and between unrelated individuals, stratified by whether mothers were normal weight or overweight or obese in early pregnancy1
| Mean difference in offspring birth weight (95% CI) per 1-kg greater gestational weight gain |
|||||
| Maternal BMI and model | n | Overall | Within siblings | Between nonsiblings | P value2 |
| g | |||||
| Normal weight [BMI (kg/m2) <25]3 | |||||
| Model 1 | 125,748 | 35.01 (34.34, 35.67) | 27.71 (25.00, 30.41) | 35.54 (34.86, 36.22) | <0.001 |
| Model 2 | 125,748 | 36.66 (36.00, 37.31) | 29.10 (26.38, 31.81) | 37.07 (36.39, 37.73) | <0.001 |
| Model 3 | 125,748 | 26.90 (26.33, 27.46) | 19.92 (17.54, 22.31) | 27.23 (26.65, 27.81) | <0.001 |
| Overweight [BMI (kg/m2) ≥25]3 | |||||
| Model 1 | 21,146 | 21.37 (19.82, 22.92) | 14.99 (8.02, 21.94) | 21.98 (20.39, 23.57) | 0.04 |
| Model 2 | 21,146 | 23.61 (22.07, 25.15) | 18.29 (11.35, 25.23) | 24.05 (22.47, 25.63) | 0.08 |
| Model 3 | 21,146 | 17.17 (15.84, 18.50) | 8.87 (2.78, 14.96) | 17.72 (16.35, 19.08) | 0.003 |
The null value is 0. Model 1 was adjusted for year of birth. Model 2 was adjusted as for model 1 plus maternal age at birth, parity, diabetes in pregnancy, and education. Model 3 was adjusted as for model 2 plus gestational age.
Obtained by using the Hausman test, testing the null hypothesis that the within-sibling and between-nonsibling associations were identical.
There was strong statistical evidence that all associations differed between women who were normal weight and those who were overweight (P for interaction <0.0001 for all).