Gonadotrophin stimulation for in vitro fertilization significantly alters the hormone milieu in follicular fluid: a comparative study between natural cycle IVF and conventional IVF.

STUDY QUESTION: Is the steroid hormone profile in follicular fluid (FF) at the time of oocyte retrieval different in naturally matured follicles, as in natural cycle IVF (NC-IVF), compared with follicles stimulated with conventional gonadotrophin stimulated IVF (cIVF)?

SUMMARY ANSWER: Anti-Mullerian hormone (AMH), testosterone (T) and estradiol (E2) concentrations are ∼3-fold higher, androstenedione (A2) is ∼1.5-fold higher and luteinizing hormone (LH) is ∼14-fold higher in NC-IVF than in cIVF follicles, suggesting an alteration of the follicular metabolism in conventional gonadotrophin stimulated IVF.

WHAT IS KNOWN ALREADY: In conventional IVF, the implantation rate of unselected embryos appears to be lower than in NC-IVF, which is possibly due to negative effects of the stimulation regimen on follicular metabolism. In NC-IVF, the intrafollicular concentration of AMH has been shown to be positively correlated with the oocyte fertilization and implantation rates. Furthermore, androgen treatment seems to improve the ovarian response in low responders.

STUDY DESIGN, SIZE, DURATION: This cross-sectional study involving 36 NC-IVF and 40 cIVF cycles was performed from 2011 to 2013. Within this population, 13 women each underwent 1 NC-IVF and 1 cIVF cycle. cIVF was performed by controlled ovarian stimulation with HMG and GnRH antagonists.

PARTICIPANTS/MATERIALS, SETTING, METHODS: Follicular fluid was collected from the leading follicles. AMH, T, A2, dehydroepiandrosterone (DHEA), E2, FSH, LH and progesterone (P) were determined by immunoassays in 76 women. Aromatase activity in follicular fluid cells was analysed by a tritiated water release assay in 33 different women. For statistical analysis, the non-parametric Mann-Whitney U or Wilcoxon tests were used.

MAIN RESULTS AND ROLE OF CHANCE: In follicular fluid from NC-IVF and from cIVF, median levels were 32.8 and 10.7 pmol/l for AMH (P < 0.0001), 47.2 and 18.8 µmol/l for T (P < 0.0001), 290 and 206 nmol/l for A2 (P = 0.0035), 6.7 and 5.6 pg/ml for DHEA (n.s.), 3292 and 1225 nmol/l for E2 (P < 0.0001), 4.9 and 7.2 mU/ml for FSH (P < 0.05), 14.4 and 0.9 mU/ml for LH (P < 0.0001) and 62 940 and 54 710 nmol/l for P (n.s.), respectively. Significant differences in follicular fluid concentrations for AMH, E2 and LH were also found in the 13 patients who underwent both NC-IVF and cIVF when they were analysed separately in pairs. Hormone analysis in serum excluded any relevant impact of AMH, T, A2, and E2 serum concentration on the follicular fluid hormone concentrations. Median serum concentrations were 29.4 and 0.9 mU/ml for LH (P < 0.0001) and 2.7 and 23.5 nmol/l for P (P < 0.0001) after NC-IVF and c-IVF, respectively. Positive correlations were seen for FF-AMH with FF-T (r = 0.35, P = 0.0002), FF-T with FF-LH (r = 0.48, P < 0.0001) and FF-E2 with FF-T (r = 0.75, P < 0.0001). The analysis of aromatase activity was not different in NC-IVF and cIVF follicular cells.

LIMITATION, REASONS FOR CAUTION: Any association between the hormone concentrations and the implantation potential of the oocytes could not be investigated as the oocytes in cIVF were not treated individually in the IVF laboratory. Since both c-IVF and NC-IVF follicles were stimulated by hCG before retrieval, the endocrine milieu in the natural cycle does not represent the pure physiological situation.

WIDER IMPLICATIONS OF THE FINDINGS: The endocrine follicular milieu and the concentration of putative markers of oocyte quality, such as AMH, are significantly different in gonadotrophin-stimulated conventional IVF compared with natural cycle IVF. This could be a cause for the suggested lower oocyte quality in cIVF compared with naturally matured oocytes. The reasons for the reduced AMH concentration might be low serum and follicular fluid LH concentrations due to LH suppression, leading initially to low follicular androgen concentrations and then to low follicular AMH production.

STUDY FUNDING/COMPETING INTERESTS: Funding for this study was obtained from public universities (for salaries) and private industry (for consumables). Additionally, the study was supported by an unrestricted grant from MSD Merck Sharp & Dohme GmbH and IBSA Institut Biochimique SA. The authors are clinically involved in low-dose monofollicular stimulation and IVF therapies, using gonadotrophins from all gonadotrophin distributors on the Swiss market, including Institut Biochimique SA and MSD Merck Sharp & Dohme GmbH. Otherwise, the authors have no competing interests.

TRIAL REGISTRATION NUMBER: Not applicable.