Effect of vitamin D deficiency on pregnancy outcomes in obese and non-obese pregnant women

Obesity and vitamin D deficiency are significant risk factors for adverse pregnancy outcomes. While lower vitamin D levels are common in obese individuals, their combined effect on perinatal outcomes remains controversial. This study aimed to evaluate the association between vitamin D deficiency and adverse perinatal outcomes in obese and non-obese pregnant women. A retrospective cohort study was conducted at SBU Konya Education and Research Hospital between June 2016 and December 2018. The study included 80 obese (BMI ≥ 30) and 80 non-obese (BMI < 30) term pregnant women without major comorbidities. Serum 25-hydroxyvitamin D levels were measured using chemiluminescence. Group comparisons were performed using Student’s t-test and chi-square test. Logistic regression analysis was used to identify risk factors for adverse perinatal outcomes. Vitamin D levels were significantly lower in obese pregnant women compared to non-obese women (10.72 ± 8.24 ng/mL vs. 15.03 ± 9.83 ng/mL, p = 0.003). Higher vitamin D levels were independently associated with a reduced risk of low birth weight in the entire cohort (OR: 0.869, 95% CI: 0.747–1.012, p = 0.046), indicating a protective effect. In obese pregnant women, increased waist circumference (OR: 1.065, 95% CI: 1.000-1.134, p = 0.049) and elevated HbA1c levels (OR: 8.869, 95% CI: 1.420-15.411, p = 0.020) were identified as independent risk factors for fetal macrosomia. Maternal vitamin D deficiency is an independent risk factor for low birth weight. In obese pregnancies, abdominal adiposity and poor glycemic control are significant predictors of fetal macrosomia. These findings highlight the potential importance of vitamin D supplementation and meticulous metabolic monitoring in obese pregnant women to improve perinatal outcomes.