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 (>4500 g). Results: On average, women with a normal BMI gained 1 kg/m² between first and second pregnancies, while women who were overweight or obese gained 1.37 kg/m². Among women with a normal BMI in their first pregnancy, a BMI increase of ≥4 kg/m² 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 (≤–2 kg/m²) 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 ≥4 kg/m² 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 (≤–2 kg/m²) 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