Association between serum vitamin D level during pregnancy and recurrent spontaneous abortion: A systematic review and meta-analysis.

PROBLEM: Previous studies had shown that there might be an association between serum vitamin D concentrations and the occurrence of recurrent spontaneous abortion (RSA). However, the conclusions remained controversial. The objective of this study was to systematically review the evidence for an epidemiological association between vitamin D and RSA.

METHOD OF STUDY: The literature search was performed in the following databases: PubMed, Web of Science, Embase and Chinese databases. The I2 statistic was used to evaluate heterogeneity. Effect sizes were calculated using fixed or random effects models, including standardized mean difference (SMD), odds ratios (OR) and their 95% confidence intervals (95% CI). Then, we performed subgroup analysis, sensitivity analysis and publication bias analysis.

RESULTS

Fourteen studies from five countries were included. Based on the results, patients with RSA had lower vitamin D levels than controls (SMD = -1.48, 95% CI: -2.01, -.94, P < .001), and pregnant women with vitamin D deficiency (VDD) had a higher risk of developing RSA (OR = 4.02, 95% CI: 2.23, 7.25, P < .001). There was remarkable heterogeneity between studies (I2SMD  = 97.3%, P < .001; I2OR  = 82.2%, P < .001). The results of the subgroup analysis suggested that heterogeneity may be caused by the assay method, age and region. Sensitivity analysis showed the analysis results were robust.

CONCLUSION

Patients with RSA had lower serum vitamin D levels than normal pregnant women, and pregnant women with VDD might be at higher risk for RSA.