The Effects of Vitamin D Supplementation before 20 Weeks of Gestation on Preeclampsia: A Systematic Review

Preeclampsia is a leading cause of maternal and fetal morbidity and mortality worldwide. The role of vitamin D supplementation during early pregnancy in the prevention of preeclampsia remains unclear. Our objective was to synthesize and critically appraise the available evidence from observational and interventional studies to determine the effects of early pregnancy vitamin D supplementation on the risk of preeclampsia. A systematic review was conducted in March 2023 using PubMed, Web of Science, Cochrane, and Scopus databases, including literature published up to February 2023. In adherence to PRISMA guidelines, a structured and systematic search strategy was employed. A total of five studies were included in the review, encompassing 1474 patients. Overall, vitamin D supplementation during early pregnancy was associated with a reduced incidence of preeclampsia in all studies (ORs ranging from 0.26 to 0.31), while others showed an increased risk of preeclampsia with low vitamin D levels during the first trimester (ORs of 4.60, 1.94, and 2.52). However, other studies found no significant protective effect but good overall safety for various vitamin D dosages administered during the first trimester. Nevertheless, variations in vitamin D dosage, the timing of supplementation, and definitions of vitamin D insufficiency may have contributed to the inconsistencies in the observed outcomes. Some studies reported significant secondary outcomes, such as a reduction in blood pressure, preterm labor, and improved neonatal outcomes, such as birth weight. The evidence from this systematic review suggests that early pregnancy vitamin D supplementation may have a role in reducing the risk of preeclampsia. However, inconsistencies in the timing of supplementation, dosages, and methodological differences between studies highlight the need for further research to determine the optimal supplementation strategy and to clarify the relationship between vitamin D and preeclampsia risk.