Maternal Vitamin D Status, Gestational Hypertension, and Preeclampsia: A Cross-Sectional Study in Urban Greece.

Background: Evidence linking maternal vitamin D status with gestational hypertensive disorders and neonatal outcomes in Southern Europe remains limited. We evaluated maternal and cord 25-hydroxyvitamin D [25(OH)D] at birth in an urban Greek cohort and examined associations with gestational hypertension and preeclampsia. Methods: We conducted a cross-sectional study of 248 mother-infant dyads delivering at Tzaneio General Hospital of Piraeus, Greece. Eligible participants were of Greek origin or long-term residents (>10 years). Maternal venous and umbilical cord blood were obtained at birth and analyzed for serum 25(OH)D. Postpartum questionnaires captured sun exposure, supplement use, and selected lifestyle factors; clinical and obstetric data, including diagnoses of gestational hypertension and preeclampsia, were abstracted from medical records. We classified 25(OH)D as deficient (<20 ng/mL), insufficient (20-29 ng/mL), and, for risk-stratified analyses, treated values < 30 ng/mL as low. Results: Maternal 25(OH)D concentrations varied seasonally (winter 16.96 ± 9.60 ng/mL; summer 24.22 ± 12.57 ng/mL) and correlated with cord concentrations (r = 0.80). Most mothers (75-89%) had <30 ng/mL across seasons, and 73% of neonates were <20 ng/mL despite supplementation. Gestational hypertension occurred in 29/248 (11.7%) and preeclampsia in 15/248 (6.0%), with low maternal 25(OH)D common among affected women. Conclusions: In this cross-sectional study of an urban Mediterranean population, hypovitaminosis D was highly prevalent among mothers and neonates, with seasonal variation and clustering among hypertensive pregnancies. These findings support prenatal care strategies beyond fixed supplementation, incorporating season- and environment-sensitive dosing with screening and dietary counseling. Prospective studies are needed to clarify causality and refine supplementation targets.