How vitamin D level influences in vitro fertilization outcomes: results of a systematic review and meta-analysis

Objective To investigate the impact of serum vitamin D level on in vitro fertilization (IVF) outcomes. Design Systematic review and meta-analysis. Setting Not applicable. Patients Infertile women undergoing conventional IVF or intracytoplasmic sperm injection (ICSI). Interventions Systematic search of PubMed, MEDLINE, EMBASE, Global Health, The Cochrane Library, Health Technology Assessment Database, and Web of Science from inception until July 2019 with cross-checking of references from relevant articles in English. Vitamin D levels were categorized into three groups: deficient ( 30 ng/mL). Before starting the data extraction, we registered the review protocol in PROSPERO (CRD42019134258). Main Outcome Measures We consider clinical pregnancy rate (CPR), live birth rate (LBR), and/or ongoing pregnancy rate (OPR) as primary outcomes. Likewise, the miscarriage rate was considered as a secondary outcome. Results Primary analysis showed that women with a replete level of vitamin D had higher CPR and LBR/OPR compared to those with a deficient of insufficient level of vitamin D. However, sensitivity analysis led to non-significant differences between the comparators for CPR (odds ratio 0.71, 95% confidence interval 0.47−1.08, I2 = 61%) and OPR/LBR (odds ratio 0.78, 95% confidence interval 0.56−1.08], I2 = 61%). Also, for miscarriage a statistically different rate was not reached. Conclusion Serum vitamin D levels do not influence IVF outcomes in terms of CPR, LBR/OPR, and miscarriage rate. Future large cohort studies are warranted to determine whether the threshold of vitamin D affects reproductive outcomes. Currently, there is a lack of consensus between the appropriate vitamin D threshold to predict reproductive outcomes compared to the one established for bone health. PROSPERO Number CRD42019134258.