The Association Between Pre-cycle Maternal Vitamin D Status and Reproductive Outcomes in Frozen-Thawed Embryo Transfer: A Systematic Review and Meta-Analysis

Vitamin D has been increasingly recognized for its potential role in reproductive physiology, particularly in endometrial receptivity and implantation. Despite growing interest, the impact of serum vitamin D status on outcomes of frozen embryo transfer (FET) cycles remains debated. The objective of this systematic review and meta-analysis was to assess the association between maternal vitamin D concentrations and reproductive success, specifically clinical pregnancy (CPR) and live birth rates (LBR), during frozen-thawed embryo transfer cycles, effectively focusing on the role of endometrial receptivity A systematic search was conducted in CENTRAL, Embase, MEDLINE, and Scopus for observational studies published until November 2025. Eligible studies compared reproductive outcomes in women with low versus normal serum 25-hydroxyvitamin D (25(OH)D) levels before autologous FET. The women were categorized as vitamin D insufficient if the level was