Impact of inter-pregnancy BMI change on perinatal outcomes: a retrospective cohort study.

OBJECTIVE: To examine the patterns and predictors of inter-pregnancy body mass index (BMI) change and its impact on perinatal outcomes in the second pregnancy.

DESIGN: Retrospective cohort study.

SETTING: Tertiary teaching hospital in Adelaide, Australia.

POPULATION: Women with their first and second consecutive, singleton deliveries occurring between 2000 and 2012 (N=5371).

METHODS: Inter-pregnancy weight change calculated based on difference between BMI at respective antenatal booking visits. Association between inter-pregnancy weight change and perinatal outcomes investigated using multivariate generalised linear models, with stratification according to initial maternal BMI category in first pregnancy.

MAIN OUTCOME MEASURES: Gestational diabetes (GDM); pregnancy induced hypertensive disorders; small-for-gestational age (SGA); preterm birth; large-for-gestational age (LGA) and macrosomia (>4500g).

RESULTS: On average, women with a normal BMI gained 1kg/m(2) between first and second pregnancies, while women who were overweight or obese gained 1.37kg/m(2). Among women with a normal BMI in their first pregnancy, a BMI increase of ≥4kg/m(2) was associated with increased risk of developing GDM (aRR 1.97; 95% CI 1.22-3.19), a macrosomic (aRR 4.06; 95% CI 2.25-7.34) or LGA infant (aRR 1.31 0.96-1.78) in the second pregnancy, while a reduction in BMI (≤-2kg/m(2)) was associated with an increased risk of SGA (aRR 1.94; 1.19-3.16). Among women who were overweight or obese in their first pregnancy, a BMI increase of ≥2-4 and ≥4kg/m(2) was associated with increased risks of developing GDM in the second pregnancy (aRR 1.39; 95% CI 1.01-1.91 and aRR 1.64 95% CI 1.16-2.31; ptrend<0.001), while no associations were observed for a BMI increase and risk of a macrosomic, SGA, or LGA infant. In contrast, reduction in BMI (≤-2kg/m(2)) was associated with a reduced risk of GDM (aRR 0.58 95% CI 0.37-0.90) and SGA (aRR 0.47; 95% CI 0.25-0.87).

CONCLUSION: Increases in BMI between pregnancies is associated with an increased risk for perinatal complications, even in normal-weight women, while a reduction in BMI is associated with improved perinatal outcomes among women who are overweight/obese. Inter-pregnancy weight control is an important target to reduce the risk of an adverse perinatal outcome in a subsequent pregnancy.