Association between perinatal outcomes and maternal pre-pregnancy body mass index

Summary Objective To quantify the association between maternal pre‐pregnancy body mass index (BMI) and perinatal outcomes. Methods We systematically reviewed and collected studies on maternal pre‐pregnancy BMI and perinatal outcomes published up to 31 August 2015. For each study, we constructed separate two‐by‐two tables to calculate the odds ratios (ORs) and 95% confidence intervals (CI). Results A total of 60 studies involving 1,392,799 women were included, and the proportions of obesity, overweight, normal weight and underweight pregnant women were 11.72%, 22.08%, 58.03% and 8.18%, respectively. When mothers were overweight or obese, their infants had a significantly higher risk of being large for gestational age (OR, 1.45, 95%CI, 1.29–1.63 and 1.88, 95%CI, 1.67–2.11, respectively), having macrosomia (OR, 1.70, 95%CI, 1.55–1.87 and 2.92, 95%CI, 2.67–3.20, respectively), being admitted to the neonatal intensive care unit (OR, 1.29, 95%CI, 1.12–1.48 and 1.91, 95%CI, 1.60–2.29, respectively) and being stillborn (OR, 1.27, 95%CI, 1.18–1.36 and 1.81, 95%CI, 1.69–1.93, respectively). When mothers were underweight, their infants had a lower risk of the aforementioned outcomes. However, mothers who were underweight had a higher risk of preterm birth (OR, 1.30, 95%CI, 1.13–1.49) and delivering an infant small for gestational age (OR, 1.67, 95%CI, 1.49–1.87). Importantly, infants had a higher risk of having a low birth weight (LBW) when their mothers were underweight (OR, 1.67, 95%CI, 1.39–2.02) or obese (OR, 1.24, 95%CI, 1.09–1.41). Conclusion Being overweight or obese was associated with an increased risk of still birth, large for gestational age, macrosomia, admission to the neonatal intensive care unit and LBW, while being underweight was associated with an increased risk of preterm birth, small for gestational age, and LBW. Women of childbearing age should maintain a normal body mass index before pregnancy.