Pre-pregnancy body mass index and weight gain during pregnancy in relation to preterm delivery subtypes.

BACKGROUND: Associations between preterm delivery (PTD) and pre-pregnancy body mass index (BMI) and pregnancy weight gain may differ across outcome subtypes.

METHODS: The authors analyzed data from 2,468 cohort participants in western Washington State, USA (1996-2005) and examined pre-pregnancy BMI and weight gain rate from pre-pregnancy to 18-22 weeks' gestation in relation to spontaneous PTD after preterm labor, spontaneous PTD after preterm premature rupture of membranes (PPROM), and indicated PTD.

RESULTS: Each 5 kg/m(2) BMI increase was associated with indicated PTD (adjusted odds ratio [OR] 1.71, 95% confidence interval [CI] 1.40-2.06). The association weakened somewhat after adjustment for hypertension and diabetes before and/or during pregnancy (5 kg/m(2) adjusted OR, 1.40; 95% CI, 1.12-1.75). Associations with spontaneous PTD and PPROM were weaker (5 kg/m(2) adjusted ORs, 0.90 and 1.14, respectively). Weight gain was associated with indicated delivery among women with normal BMI (0.1 kg/week adjusted OR, 1.22; 95% CI, 1.02-1.45) but not among overweight or obese women (adjusted OR, 1.02; 95% CI, 0.87-1.20). Weight gain was inversely associated with spontaneous PTD (0.1 kg/week adjusted OR, 0.87; 95% CI, 0.77-0.99) and not strongly associated with PPROM (adjusted OR, 1.03; 95% CI, 0.90-1.17).

CONCLUSIONS: Pre-pregnancy overweight increases indicated PTD risk independently of hypertension and diabetes. High early pregnancy weight gain increases indicated PTD risk in women with a normal BMI.