Meta‐analysis of the effect of the maternal vitamin D level on the risk of spontaneous pregnancy loss

Background The association between vitamin D deficiency and early spontaneous pregnancy loss (SPL) is unclear. Objectives To assess the association of serum 25-hydroxyvitamin D (25(OH)D) and SPL. Search strategy Embase, PubMed, and Web of Science were searched for relevant papers published before February 20, 2016, using search terms including “vitamin D” and “pregnancy loss.” Selection criteria Case–control and cohort studies investigating the relationship of maternal serum 25(OH)D and SPL were included. Data collection and analysis Two authors independently extracted original data from the selected papers. The DerSimonian–Laird random-effects model was used to perform the meta-analysis. Heterogeneity was assessed by calculating I2. Main results Five studies, including 10 630 pregnant women, met the inclusion criteria. There was no significant association between a low 25(OH)D level and an increased risk of SPL. In a subgroup analysis, an extremely low 25(OH)D level (<20 ng/mL) was significantly associated with an increased risk of SPL in the first trimester (relative risk 2.24, 95% confidence interval 1.15–4.37); the heterogeneity across studies was not significant (I2=0.0%, P=0.355). Conclusions Severe Vitamin D deficiency could be detrimental to early embryonic development and increase the risk of early SPL.