Women's vitamin D levels and IVF results: a systematic review of the literature and meta-analysis, considering three categories of vitamin status (replete, insufficient and deficient)

To investigate the influence of vitamin D status onin vitrofertilisation (IVF) results, a meta-analysis of 15 cohort studies of 3711 women undergoing IVF was performed. Women were classified into three groups according their vitamin D levels (>= 30 ng/mL considered replete/sufficient; 21-29 ng/mL insufficient and <20 ng/mL deficient). Three different meta-analyses were performed: (i) sufficient vs deficient; (ii) sufficient vs 'insufficient + deficient'; (iii) 'sufficient + insufficient' vs deficient. Comparing IVF outcomes in sufficient versus deficient groups (considering autologous and donor oocyte cycles together), we found women with sufficient vitamin D had significantly higher biochemical pregnancy (OR = 1.43 [1.06-1.95]), ongoing pregnancy (OR = 1.29 [1.02-1.64]), and live birth (OR = 1.74 [1.31-2.31]) rates, with a non-significant trend to a higher clinical pregnancy rate (OR = 1.31 [0.94-1.82]), whereas implantation and miscarriage rates were similar. When the meta-analysis was restricted to autologous oocytes, the parameters which had been significant in the joint analysis remained significant, and differences in implantation (OR = 1.64, [1.17-2.29]) and clinical pregnancy (OR = 1.47 [1.2-1.69]) rates became significant. No significant differences were found when considering only cycles with donor oocytes. The sufficient + insufficient vs deficient and sufficient vs 'insufficient + deficient' comparisons identified significant differences in live birth rate. The meta-analysis shows that sufficient vitamin D status is associated with better outcomes in IVF. Nonetheless, there are many demographic, geographic and clinical parameters that may be related to vitamin D status that need to be ascertained before concluding that the better results are due to the higher levels of vitamin D.