The relationship between vitamin D and abortion: a systematic review and meta-analysis

Introduction: Spontaneous abortion is one of the common complications of pregnancy that its etiology is unknown. Since vitamin D deficiency may be one of its causes, this systematic review was performed with aim to evaluate the relationship between vitamin D and abortion. Methods: In this systematic review and meta-analysis, the literature published from 1990 until the end of 2019 were searched in databases of PubMed, Embase, Cochrane Library, Scopus, Web of Science, SID, Magiran, IranMedex with the keywords of Vitamin D, 25-hydroxyvitamin, 25-Dihydroxyvitamin D3, Pregnancy loss, fetal loss, miscarriage and abortion and the equivalent Persian keywords. The quality of the papers was examined using Ottawa checklist, and STATA software was used for the meta-analysis. Results: Among 311 papers found in the first stage, finally 5 papers (5203 individuals) met the study criteria. In terms of methodological quality, all of the included articles were of average level. The findings of the studies included in the meta-analysis showed that there is a relationship between low levels of vitamin D and abortion (Effect size: 0.02; 95 Confidence Interval: -0.02 to 0.06). Conclusion: The results of the meta-analysis suggested a relationship between serum level of vitamin D and abortion; thus, it can be concluded that low levels of vitamin D are considered as a risk factor for abortion.