The effect of vitamin D supplementation in pregnancy on the incidence of preeclampsia: A systematic review and meta-analysis

Introduction: The results of previous studies regarding the effect of vitamin D on the incidence of preeclampsia are inconsistent. Therefore, the primary objective of the present review was to determine the effect of vitamin D supplementation during pregnancy on the risk of preeclampsia. Methods: Five major scientific databases were searched from inception to June 10, 2023. Studies with randomized controlled trial designs were identified. To assess the methodological quality of the selected studies, the Cochrane Tool Checklist (CTC) was used. The random effect model was chosen as a combination model. Statistical heterogeneity was evaluated using the standard chi 2 test, and the intensity of heterogeneity was calculated using I2. Effect size indicators including risk ratio (RR), risk difference (RD), and number needed to treat (NNT) were calculated with estimated 95 % confidence intervals. Results: Nineteen studies were included in the systematic review and meta -analysis. The pooled RR of preeclampsia in the intervention group compared to the control group was 0.61 (95 % CI, 0.47 to 0.78; I2=14.4 %; chi 2=23.37; p = 0.27; tau2=0.05), and indicated a 39 % reduction in the risk of preeclampsia. The pooled RD of preeclampsia in the intervention group compared to the control group was -0.03 (95 % CI: -0.05 to -0.01; I2=45.5 %; chi 2=36.68; p = 0.01; tau2=0.0008) and the difference in the risk of preeclampsia among women who received vitamin D supplements was 3 % less than the control group. The NNT was 29 (95 % CI: 20 to 52). Conclusion: Vitamin D supplementation significantly reduces preeclampsia during pregnancy.