Vitamin D and assisted reproductive treatment outcome: a systematic review and meta-analysis.

STUDY QUESTION Is serum vitamin D associated with live birth rates in women undergoing ART? SUMMARY ANSWER Women undergoing ART who are replete in vitamin D have a higher live birth rate than women who are vitamin D deficient or insufficient. WHAT IS KNOWN ALREADY Vitamin D deficiency has been associated with an increased risk of abnormal pregnancy implantation as well as obstetric complications such as pre-eclampsia and fetal growth restriction. However, the effect of vitamin D on conception and early pregnancy outcomes in couples undergoing ART is poorly understood. STUDY DESIGN, SIZE, DURATION A systematic review and meta-analysis of 11 published cohort studies (including 2700 women) investigating the association between vitamin D and ART outcomes. PARTICIPANTS/MATERIALS, SETTINGS, METHODS Literature searches were conducted to retrieve studies which reported on the association between vitamin D and ART outcomes. Databases searched included MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials and CINAHL. Eleven studies matched the inclusion criteria. MAIN RESULTS AND THE ROLE OF CHANCE Live birth was reported in seven of the included studies (including 2026 patients). Live birth was found to be more likely in women replete in vitamin D when compared to women with deficient or insufficient vitamin D status (OR 1.33 [1.08-1.65]). Five studies (including 1700 patients) found that women replete in vitamin D were more likely to achieve a positive pregnancy test than women deficient or insufficient in vitamin D (OR 1.34 ([1.04-1.73]). All 11 of the included studies (including 2700 patients) reported clinical pregnancy as an outcome. Clinical pregnancy was found to be more likely in women replete in vitamin D (OR 1.46 [1.05-2.02]). Six studies (including 1635 patients) reported miscarriage by vitamin D concentrations. There was no association found between miscarriage and vitamin D concentrations (OR 1.12 [0.81-1.54]. The included studies scored well on the Newcastle-Ottawa quality assessment scale. LIMITATIONS REASONS FOR CAUTION Although strict inclusion criteria were used in the conduct of the systematic review, the included studies are heterogeneous in population characteristics and fertility treatment protocols. WIDER IMPLICATIONS OF THE FINDINGS The findings of this systematic review show that there is an association between vitamin D status and reproductive treatment outcomes achieved in women undergoing ART. Our results show that vitamin D deficiency and insufficiency could be important conditions to treat in women considering ARTs. A randomized controlled trial to investigate the benefits of vitamin D deficiency treatment should be considered to test this hypothesis. STUDY FUNDING/COMPETING INTERESTS No external funding was either sought or obtained for this study. The authors have no competing interests to declare. REGISTRATION NUMBER N/A