Association of Gestational Weight Gain With Preterm Birth Among Women of Normal Pre-pregnancy Body Mass Index: A Matched Case-Controlled Study

Background: Preterm birth (PTB), i.e., delivery before 37 weeks, is a major cause of neonatal morbidity and mortality. Gestational weight gain (GWG) influences PTB risk, with both inadequate and excessive gain linked to adverse outcomes. Objective: To assess the association between GWG and PTB among women with normal pre-pregnancy BMI. Methods: A matched case-control study was conducted at the Women and Children’s Hospital, Jawaharlal Institute of Postgraduate Medical Education and Research, India. Women with spontaneous preterm delivery (28-36 weeks; n = 90) were matched in a ratio of 1:4 by age (±2 years) and parity with term controls (n = 360). GWG was calculated as the difference between pre-pregnancy and delivery weight and categorised per the Institute of Medicine (IOM) guidelines as inadequate, adequate, and excessive. Maternal sociodemographic, obstetric, and clinical data were collected from records and interviews. Conditional logistic regression evaluated associations between GWG and PTB, adjusting for confounders. Results: Cases had a lower mean GWG than controls (6.77 ± 2.17 vs. 8.91 ± 1.86 kg, p < 0.001) but delivered six weeks earlier, limiting weight gain. After adjusting for gestational age, GWG was not independently associated with PTB. Higher maternal education was protective (OR: 0.41; 95% CI: 0.18-0.98), whereas prior caesarean increased risk (OR: 5.23; 95% CI: 1.87-14.67). Conclusion: Extremes of GWG were not independently associated with PTB in women with normal BMI. Higher maternal education was protective, whereas prior caesarean increased risk. Monitoring GWG and promoting maternal health literacy may help prevent preterm deliveries.