Impact of early pregnancy body mass index and gestational weight gain on birth outcomes: Findings from a pregnancy cohort in South Delhi, India

Early pregnancy low body mass index (BMI) and inadequate gestational weight gain (IGWG) are significant risk factors for adverse birth outcomes. However, the specific risks among underweight women with IGWG or excessive GWG (EGWG), as well as overweight/obese women with IGWG or EGWG, compared to normal BMI women with adequate GWG (AGWG), remain poorly defined.The primary objective is to estimate the risk of small for gestational age (SGA) among women with underweight at early pregnancy and IGWG compared to women with normal weight at early pregnancy and AGWG. Data were derived from a randomized factorial trial. BMI was assessed at <14 weeks of gestation, and women weight was measured monthly until 32 weeks, biweekly until 36 weeks and weekly until delivery. GWG was classified as per Institute of Medicine (IOM) guidelines. Infant weight and length were measured <14 days of birth. Regression analysis assessed associations (risk ratio, RR) between BMI, GWG, and birth outcomes. The highest prevalence of SGA (62.4%; 95%CI 57.1-67.5) was observed among underweight women with IGWG. Normal BMI women with IGWG (aRR 1.36; 95%CI 1.21-1.53) and underweight women with IGWG (aRR 1.65; 95%CI 1.44-1.89) increased, and overweight/obese women with excessive GWG (EGWG) reduced risk of SGA (aRR 0.56; 95%CI 0.43-0.72), compared to normal BMI women with AGWG. IGWG among normal women (aRR 1.43; 95%CI 1.21-1.70) and IGWG among underweight women (aRR 2·09; 95%CI 1·74-2·52) also increased, and overweight/obese women with EGWG (aRR 0.73; 95%CI 0.54-0.98) reduced the risk of low birth weight (LBW). Underweight women with IGWG face the highest risk of adverse outcomes, while EGWG among overweight or obese women reduces the risk of adverse outcomes. Monitoring of GWG alongside early pregnancy BMI is essential for guiding targeted nutritional intervention to improve pregnancy outcomes.