Endocrine Abstracts

Background: Numerous studies have suggested that optimal vitamin D status increases treatment success of women undergoing assisted reproductive treatments. However, conflicting data exist, and the relationship remains controversial, prompting the need for more comprehensive studies investigating all the metabolites of vitamin D in women undergoing IVF/ICSI treatment.

Objective: To investigate the relationship between follicular fluid levels of the three main vitamin D metabolites 25OHD₃, 24,25(OH)₂D₃ and 1,25(OH)₂D₃ and IVF/ICSI treatment outcome.

Study design: Follicular fluid and serum samples from 116 women undergoing IVF/ICSI treatment were analyzed. Expression of the vitamin D regulating enzymes (CYP2R1, CYP27B1, CYP24A1) and the vitamin D receptor (VDR) was investigated in human ovaries.

Results: The vitamin D regulating enzymes CYP2R1, CYP27B1, CYP24A1 and VDR were expressed in the human ovary, enabling the follicles to activate, inactivate and respond to vitamin D metabolites. Moreover, all three investigated vitamin D metabolites 25OHD₃, 24,25(OH)₂D₃ and 1,25(OH)₂D₃ were present in follicular fluid and in serum. 25OHD levels were similar in serum and follicular fluid, while levels of 24,25(OH)₂D₃ were higher and 1,25(OH)₂D₃ lower in follicular fluid than in serum. Upon stratifying women according to live birth outcome, women achieving a live birth had significantly higher follicular fluid levels of the 24,25(OH)₂D₃ metabolite (17.4 ± 8.5 vs 13.5 ± 6.3 nmol/l, P=0.015) and a higher 24,25(OH)₂D₃/25OHD₃ ratio (0.25 ± 0.07 vs 0.21 ± 0.07, P=0.029) compared to women with an unsuccessful cycle. Also, when grouping women in intervals according to their follicular fluid 24,25(OH)₂D₃/25OHD₃ ratio the live birth rate significantly increased across increasing ratio intervals (15%, 20% and 50% for the <0.2, 0.2-0.3 and >0.3 group, respectively, P=0.019).

Conclusions: This study reveals that a higher follicular fluid 24,25(OH)₂D₃ level and 24,25(OH)₂D₃/25OHD₃ ratio is associated with increased live birth rate in women undergoing IVF/ICSI treatment.