Effect of early vitamin D supplementation on the incidence of preeclampsia in primigravid women: a randomised clinical trial in Eastern Democratic Republic of the Congo

Background: Previous studies have reported the association between maternal vitamin D deficiency and preeclampsia. However, the efficacy of vitamin D supplementation in reducing the occurrence of preeclampsia remains unclear. The objective of this study was to evaluate the effect of cholecalciferol supplementation on the incidence of preeclampsia in primigravid women and its related maternal and foetal outcomes.

Methods: A single-blinded clinical trial was conducted in fourteen antenatal care health facilities in the North (Goma, Mwesso, Nyiragongo) and South Kivu (Bukavu-Panzi) provinces of the Democratic Republic of Congo from March 1, 2020, to June 30, 2021. A total of 1300 primigravid women not exceeding 16 weeks of gestation were randomised with a 1:1 ratio to either the supplemented (A) or control (B) group. Each pregnant woman (A) presenting for antenatal care received a single monthly dose of cholecalciferol (60,000 IU) orally for 6 months. The control group received no vitamin D supplementation or placebo. Serum 25(OH)D was measured at recruitment and at 34 weeks of gestation. Outcomes were assessed monthly until delivery.

Results: The median maternal age was 21 years (14-40), while the median gestational age was 15 weeks (5.4-29.0). A significant reduction in the risk of preeclampsia [RR = 0.36 (0.19-0.69); p = 0.001] and preterm delivery [RR = 0.5 (0.32-0.78); p = 0.002] was observed in the intervention group. An RR of 0.43 [(0.27-0.67); p < 0.001] was found for low birth weight. The RR for caesarean section was 0.63 [(0.52-0.75); p < 0.001]. The APGAR score at the 5th minute (p = 0.021) and the size of the newborn were significantly higher in the supplemented group (p = 0.005).

Conclusion: A single monthly dose (60,000 IU) of vitamin D supplementation, started in earlypregnancy, significantly reduced the incidence of preeclampsia and its maternal and foetal complications.

Trial registration: ISRCTN Register with ISRCTN46539495 on 17 November 2020.