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

<b>Introduction:</b> 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. <b>Methods:</b> 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. <b>Results:</b> Vitamin D insufficiency and deficiency affected 32.3% and 18.9% of mothers, respectively. Supplementation was the strongest predictor of sufficiency (<i>p</i> < 0.01), showing a dose-response effect (r = 0.84, <i>p</i> < 0.01). Maternal and neonatal 25(OH)₂D levels were strongly correlated (r = 0.99, <i>p</i> < 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. <b>Conclusions:</b> 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.