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 I-2. Main results: Five studies, including 10630 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 (I-2=0.0%, P=0.355). Conclusions: Severe Vitamin D deficiency could be detrimental to early embryonic development and increase the risk of early SPL.