Vitamin D Deficiency and Its Association With Preterm Birth From January 2016 to March 2024: Eight Years of Effect [ID 1566]

INTRODUCTION: Maternal vitamin D status has been shown to influence pregnancy outcomes and is a key focus of maternal health initiatives at the Medical University of South Carolina (MUSC). Debate about the benefits of vitamin D supplementation is ongoing, and recommendations for supplementation and monitoring vary among health care organizations. The objective of this study was to describe the association of vitamin D levels with gestational age at delivery. METHODS: We conducted a retrospective chart review of 15,506 women who had 25-hydroxyvitamin D [25(OH)D] concentrations measured during pregnancy and delivered at MUSC from January 2016 to March 2024. Women with cancer, HIV, or participation in vitamin D supplementation trials were excluded. 25(OH)D concentrations were compared to the gestational age at delivery. RESULTS: The overall mean ± SD 25(OH)D concentration was 34.2±17 ng/mL. Mothers delivering before 37 weeks had significantly lower 25(OH)D (30.4±17.4 ng/mL) compared to those delivering at 37 weeks or later (34.8±17.3 ng/mL), with a mean difference of −4.4 ng/mL (95% CI, −5.23 to −3.62; P <.0001). This difference was accentuated among mothers delivering less than 32 weeks (26.3±14.9 ng/mL) compared to those delivering at 32 weeks or later (34.4±17.4 ng/mL), with a mean difference of 8.2 ng/mL (95% CI, 6.43 to 9.94; P <.0001). CONCLUSIONS/IMPLICATIONS: Lower maternal 25(OH)D concentrations are significantly associated with preterm delivery. Ensuring adequate vitamin D status during pregnancy remains an underutilized public health intervention to reduce preterm birth.