Relationship of Maternal 25-Hydroxyvitamin D₃ Deficiency With the Occurrence of Preterm Labor

Preterm labor remains a major contributor to neonatal morbidity and mortality, particularly in regions where nutritional deficiencies are common.  Objective: This study assessed the relationship between maternal vitamin D₃ deficiency and the occurrence of preterm labor.  Methods: This cross-sectional analytical study was conducted at Central Park Teaching Hospital, Lahore, from December 2023 to December 2024, and included 316 pregnant women. Participants were categorized into a preterm labor group (n = 148) and a term delivery group (n = 168). Serum 25-OH-D₃ levels were measured using a chemiluminescent immunoassay and classified as deficient, insufficient, or sufficient.  Results: Vitamin D₃ deficiency was highly prevalent (67.1%) and significantly more common in women with preterm labor (80.4%) than those with term deliveries (55.4%) (p < 0.001). Mean serum vitamin D₃ levels were markedly lower in the preterm group (15.8 ± 5.9 ng/mL) compared with the term group (22.4 ± 7.1 ng/mL) (p < 0.001). Logistic regression demonstrated that vitamin D₃ deficiency remained an independent predictor of preterm labor (adjusted OR = 2.51, 95% CI: 1.62-3.89). Additional significant factors included hemoglobin <10 g/dL (aOR = 1.68), sun exposure <30 minutes/day (aOR = 1.74), antenatal visits <4 (aOR = 1.82), and previous preterm birth (aOR = 1.91).  Conclusions: Maternal vitamin D₃ deficiency is strongly associated with preterm labor and remains a significant independent predictor even after adjusting for clinical and demographic factors. Given its high prevalence and modifiable nature, routine screening and targeted vitamin D₃ supplementation may help reduce the burden of preterm birth.