The Influence of Vitamin D Levels on IVF Outcomes: A Systematic Review

Abstract

Vitamin D has been implicated in reproductive health, with potential effects on in vitro fertilization (IVF) outcomes. However, existing evidence remains conflicting. This systematic review evaluates the association between vitamin D levels and IVF success, including embryo quality, clinical pregnancy, and live birth rates. A comprehensive search of PubMed, Web of Science, Scopus, and Embase was conducted following PRISMA guidelines. Thirty studies (randomized controlled trials, prospective/retrospective cohorts) were included after screening 1,393 records. Data on vitamin D status (deficient [<20 ng/mL], insufficient [20–29 ng/mL], sufficient [≥30 ng/mL]) and IVF outcomes were extracted and qualitatively synthesized. Risk of bias was assessed using the Newcastle-Ottawa Scale and Cochrane tools. Findings were heterogeneous. Some studies reported improved embryo quality (e.g., higher blastocyst formation) and pregnancy rates with sufficient vitamin D (e.g., ≥30 ng/mL), particularly in women with polycystic ovary syndrome (PCOS) or thyroid autoimmunity. However, others found no significant association, including a large RCT showing no benefit from supplementation. Live birth rates were lower in deficient women in two studies (7.1% vs. 46%). Subgroup analyses highlighted variability by age, BMI, and genetic factors (e.g., VDR polymorphisms). While vitamin D sufficiency may enhance certain IVF outcomes, evidence is inconsistent, and optimal thresholds remain unclear. Routine supplementation cannot yet be universally recommended, but screening for deficiency appears prudent. Future research should prioritize standardized measurements and large RCTs focusing on live birth rates.