Association of Maternal Body Mass Index with Pregnancy Outcomes and Drug Utilization Patterns: A Prospective Observational Study

<title>Abstract</title> <p>Background Maternal body mass index (BMI) is a pivotal determinant of obstetric risk, yet its combined influence on pregnancy-related outcomes and patterns of drug utilization remains inadequately characterized in low- and middle-income country settings. Methods A prospective observational study was conducted among 264 pregnant women with singleton pregnancies attending a tertiary care teaching hospital in southern India between September 2025 and February 2026. Participants were enrolled consecutively and classified into underweight, normal weight, overweight, and obese categories according to the World Health Organization body mass index (BMI) classification. Sociodemographic, obstetric, neonatal, and medication utilization data were collected prospectively until delivery using a structured case report form. Drug utilization patterns were evaluated using the World Health Organization core prescribing indicators. Associations between maternal BMI and pregnancy outcomes were initially assessed using the Chi-square test, Fisher's exact test, and one-way analysis of variance. Multivariable logistic regression analyses were performed to identify independent predictors of maternal and neonatal outcomes, while multiple linear regression analyses were used to identify predictors of medication utilization and length of hospital stay. Statistical significance was defined as a two-sided P &lt; 0.05. Results The mean maternal age was 26.8 ± 4.1 years; 46.6% had normal BMI, 27.3% were overweight, and 15.5% were obese. Increasing BMI was significantly associated with gestational diabetes mellitus (GDM: 3.6% vs 31.7% in underweight vs obese; p &lt; 0.001), pregnancy-induced hypertension (7.1% vs 34.1%; p &lt; 0.001), pre-eclampsia (3.6% vs 26.8%; p = 0.002), and caesarean delivery (21.4% vs 63.4%; p &lt; 0.001). Underweight mothers had the highest rates of low birth weight neonates (28.6%; p = 0.01), while macrosomia (17.1%; p &lt; 0.001) and neonatal intensive care unit (NICU) admission (22.0%; p = 0.03) peaked in the obese group. The mean number of drugs prescribed per patient increased from 2.1 ± 0.9 (underweight) to 4.1 ± 1.5 (obese; p &lt; 0.001). Antidiabetic agents, antihypertensives, and antibiotics were prescribed significantly more frequently in overweight and obese women (all p &lt; 0.05). Injectable drug use (p = 0.03) and mean duration of hospitalisation (3.2 ± 1.1 vs 5.2 ± 1.8 days; p &lt; 0.001) increased progressively with BMI. Overall, 87.5% of drugs were from the Essential Medicines List and 74.2% were prescribed by generic name. Conclusions Elevated maternal BMI is associated with an independently increased risk of obstetric complications, adverse neonatal outcomes, and pharmacological exposure. Routine BMI-based antenatal risk stratification, early screening for metabolic and hypertensive disorders, and rational prescribing guided by WHO principles are essential interventions for optimising maternal and neonatal health in resource-limited settings. Although multivariable analyses were performed to adjust for important confounders, the observational design precludes causal inference.</p>