Maternal Obesity and Outcomes During Pregnancy and the Puerperium: A Single-Center Retrospective Observational Study

Background: Maternal obesity is associated with pregnancy complications and adverse perinatal outcomes, although observational associations may be influenced by confounding, exposure ascertainment, and missing data. This study investigated associations between recorded maternal body mass index (BMI) and maternal clinical conditions, obstetric complications, delivery characteristics, and perinatal outcomes in a referral center. Methods: A retrospective study was conducted using medical records of pregnant women at a referral center. Recorded maternal BMI categories were classified according to the World Health Organization. Database standardization harmonized equivalent diagnostic terms, preserved maternal clinical conditions and obstetric complications as separate domains, and grouped uncommon conditions for descriptive and exploratory analyses. Missing non-BMI variables underwent multiple imputation across 50 completed datasets; maternal BMI was not imputed. Twin pregnancies were excluded, and women with and without recorded BMI were compared before and after imputation. All singleton pregnancies with recorded BMI were included descriptively, whereas association analyses excluded women with underweight because of their small number and absence of recorded primary-outcome events. The primary composite perinatal outcome comprised neonatal intensive care unit admission, recorded fetal death or stillbirth, or a 5-min Apgar score <7 among liveborn infants. Logistic regression models compared overweight and obesity with normal weight, adjusting for maternal age and parity. Selected outcomes underwent additional adjustment for smoking, chronic hypertension, and pre-existing diabetes mellitus. Complete-case analyses assessed the sensitivity of the core findings. Results: The source database comprised 1012 records. After excluding 13 twin pregnancies, 999 singleton pregnancies remained; BMI was recorded for 787 women and missing for 212 (21.2%). Among women with recorded BMI, 27 (3.4%) had underweight, 282 (35.8%) normal weight, 210 (26.7%) overweight, and 268 (34.1%) obesity. Association analyses included 760 women. Compared with normal weight, obesity was associated with maternal clinical conditions (adjusted odds ratio, 3.04; 95% confidence interval, 2.06-4.49), chronic hypertension (8.96; 4.14-19.38), obstetric complications (4.12; 2.83-5.99), hypertensive disorders of pregnancy (6.12; 3.60-10.40), gestational diabetes mellitus (2.43; 1.48-3.97), cesarean delivery (3.18; 2.12-4.75), and large-for-gestational-age birth (5.99; 2.74-13.13). Overweight was also associated with obstetric complications, gestational diabetes mellitus, cesarean delivery, and large-for-gestational-age birth. The associations between obesity and overall obstetric complications, hypertensive disorders of pregnancy, and large-for-gestational-age birth remained evident in expanded models. No statistically significant association was observed with the primary composite outcome for overweight (0.58; 0.21-1.57) or obesity (1.16; 0.54-2.53), and complete-case analyses were similarly inconclusive. Core models did not identify statistically significant associations with preterm birth, small-for-gestational-age birth, or low birth weight. The exploratory association with perineal tears was attenuated after adjustment. Women without recorded BMI had fewer recorded maternal clinical conditions, obstetric complications, and cesarean deliveries, but more composite perinatal events; these differences persisted after imputation. Conclusions: Higher recorded maternal BMI was associated with maternal morbidity, cesarean delivery, and large-for-gestational-age birth after adjustment for age and parity. The composite perinatal findings remained inconclusive because of limited event frequency and imprecise estimates, rather than demonstrating absence of increased risk. Differences according to BMI availability indicate potential selection bias, while uncertain exposure timing and residual confounding further constrain interpretation. The findings support individualized preconception and antenatal assessment and standardized clinical documentation, without establishing causal relationships or the effectiveness of a specific intervention.