Vitamin D Supplementation During Pregnancy and Maternal and Neonatal Vitamin D Status at ≤32 Weeks Gestation: Romanian Prospective Observational Cohort Study

<b>Background</b>: Recently, vitamin D deficiency (VDD) has been described as a pandemic, affecting all groups of the population. Pregnant women and preterm infants are particularly vulnerable to vitamin D deficiency. <b>Objectives</b>: We aimed to evaluate the maternal and neonatal vitamin D status in relation with maternal vitamin D supplementations during pregnancy and to identify demographic, social, and healthcare risk factors for maternal VDD and vitamin D insufficiency in women delivering at ≤32 weeks of gestation. <b>Methods</b>: This prospective observational study was developed in the regional level III maternity unit of the Clinical County Emergency Hospital Sibiu. It included all admitted mothers who delivered at ≤32 weeks of gestation and their infants between 1 March 2022 and 28 February 2025. Infant deaths in the first 24 h of life, major congenital defects, chromosomal abnormalities, the admission of outborn infants without their mothers, or the transfer of the mother more than 48 h after birth were used as exclusion criteria. Maternal and neonatal data were collected from medical records. Data on maternal vitamin D supplementation were collected through interviews. Univariate and multivariate logistic regressions, linear regression, and predictive models were performed for data analysis. <b>Results</b>: A total of 146 mothers (median (IQR) age 30 (24-35) years) and their 164 preterm infants born at ≤32 weeks of gestation (median gestational age of 30 (27-31) weeks and birth weight of 1200 (900-1527) g) were included in this study. Only 43.15% of the mothers used multivitamins containing vitamin D during pregnancy, and 10.96% used specific vitamin D supplements. Vitamin D supplementation was used for a median of 4 (3-5) months at a median dose of 800 (250-1500) IU/day. Severe VDD (25(OH)D < 10 ng/mL), VDD (25(OH)D < 20 ng/mL), VDI (25(OH)D 20-29 ng/mL) were found in 19.86%, 55.48%, and 23.97% of the mothers and 16.46%, 58.53%, and 25.61% of their infants, respectively. A significant correlation was found between the maternal and neonatal status (r = 0.684, r² = 0.468, <i>p</i> < 0.001, B = 0.62). Both the maternal and neonatal vitamin D status were correlated with the vitamin D duration and dose used for supplementation during pregnancy. The logistic regression analysis showed that birth during a cold season and increased parity are independently associated with severe maternal VDD, while birth during the cold season and a lower educational status were independently associated with maternal VDD. Only an absent vitamin D supplementation (in the form of a multivitamin or specific vitamin D supplements) has been proven as an independent risk factor for VDI. <b>Conclusions</b>: Our findings revealed a worrisome prevalence of severe VDD, VDD, and VDI in mothers delivering very prematurely and in their infants. Additionally, less than half of the mothers in this study used vitamin D supplements during pregnancy despite the national recommendations. The professionals involved in advising pregnant women and policymakers should find solutions to improve the vitamin D status in these vulnerable groups of the population.