Maternal Vitamin D Status and Its Association with Neonatal Health: Clinical Implications and Influencing Factors

Introduction: Adequate maternal vitamin D status during pregnancy is essential for fetal skeletal development and neonatal vitamin D reserves. Evidence from Central and Eastern Europe on maternal deficiency, its determinants, and supplementation effectiveness in late pregnancy is limited. This study assessed the impact of 2000 IU/day and 4000 IU/day maternal vitamin D supplementation during the third trimester, compared to no supplementation, on maternal and neonatal 25-hydroxyvitamin D 25(OH)2D levels at birth, and explored sociodemographic, obstetric, dietary, and lifestyle factors affecting vitamin D status. Methods: In a cross-sectional study at Târgu Mureș County Clinical Hospital, Romania, 322 term mother–newborn pairs (37–41 weeks) from January 2021 to July 2023 were evaluated. The maternal and umbilical cord 25(OH)2D was measured via electrochemiluminescence immunoassay. Data on socioeconomic status, parity, sun exposure, diet, and supplementation were collected through questionnaires and records. Statistical analysis included chi-square, linear regression, and multivariate modeling. Results: Vitamin D insufficiency and deficiency affected 32.3% and 18.9% of mothers, respectively. Supplementation was the strongest predictor of sufficiency (p < 0.01), showing a dose–response effect (r = 0.84, p < 0.01). Maternal and neonatal 25(OH)2D levels were strongly correlated (r = 0.99, p < 0.01). Although several factors correlated with deficiency in univariate analyses, only supplementation remained significant in multivariate models. No link was found between 25(OH)2D status and neonatal anthropometrics or early complications. Conclusions: A high prevalence of vitamin D deficiency has been documented among pregnant women in Romania. High-dose supplementation during late pregnancy is critical to ensure sufficient maternal and neonatal vitamin D, highlighting the need for standardized antenatal supplementation protocols, especially in disadvantaged groups.