Vitamin D as a follicular marker of human oocyte quality and a serum marker of in vitro fertilization outcome

Purpose This study investigated the relationship between the vitamin D [25(OH) D] level in individual follicles and oocyte developmental competence. Methods A prospective cohort study in a private infertility center. Infertile women (N = 198) scheduled for intracytoplasmic sperm injection (ICSI) and a single embryo transfer (SET) provided serum samples and 322 follicular fluid (FF) specimens, each from a single follicle on the day of oocyte retrieval. Results FFs corresponding to successfully fertilized oocytes (following ICSI) contained significantly lower 25(OH) D level compared with those that were not fertilized (28.4 vs. 34.0 ng/ml, P = 0.001). Top quality embryos on the third day after fertilization, when compared to other available embryos, developed from oocytes collected from follicles containing significantly lower 25(OH) D levels (24.56 vs. 29.59 ng/ml, P = 0.007). Positive hCG, clinical pregnancy, and live birth rates were achieved from embryos derived from oocytes that grew in FF with significantly lower 25(OH) D levels than in follicles not associated with subsequent pregnancy. The concentration of 25(OH) D in FF in women with negative hCG was 32.23 +/- 20.21 ng/ml, positive hCG 23.62 +/- 6.09 ng/ml, clinical pregnancy 23.13 +/- 6.09 ng/ml, and live birth 23.45 +/- 6.11 ng/ml (P < 0.001). Women with serum 25(OH) D < 20 ng/ml had not only a higher fertilization rate (71 vs. 61.6%, P = 0.026) and a higher clinical pregnancy rate (48.2 vs. 25%, P = 0.001), but also higher miscarriage rate (14.5 vs. 3.8%, P = 0.013) compared with those with levels >= 20 ng/ml. Conclusion This study reveals that the level of 25(OH) D in FF correlates negatively with the oocytes' ability to undergo fertilization and subsequent preimplantation embryo development. Oocytes matured in FF with low 25(OH) D concentration are more likely to produce top quality embryos and are associated with higher pregnancy and delivery rates. On the other hand, low serum vitamin D concentration is associated with higher miscarriage rates.