P-682 Androgen and Inhibin B levels during ovarian stimulation before and after eight weeks of low dose hCG priming in women with low ovarian reserve
Authors: Wang N F , Bogstad J W , Rønn Petersen M , Pinborg A , Yding Andersen C , Løssl K 
Published: June 2023

Abstract

Study question
Does eight weeks of low dose human chorionic gonadotropin (hCG)-priming affect androgen or Inhibin B levels in serum and follicular fluid during IVF/ICSI treatment?

Summary answer
Inhibin B was reduced on stimulation day 1 in the IVF/ICSI cycle following hCG-priming. Androgen levels in serum and follicular fluid was not increased.

What is known already
In our recently published pilot study, eight weeks of low-dose hCG-priming was used to stimulate the intraovarian androgen synthesis in women with AMH &lt;6.29 pmol/L. Priming resulted in more retrieved oocytes and more follicles sized 2-5 mm and less sized 6-10 mm at the start of stimulation. Stimulation time and FSH consumption was increased after priming. HCG priming potentially stimulate the intraovarian androgen synthesis causing upregulation of FSH receptors on granulosa cells, and therefore it was unexpected that the antral follicles were smaller and stimulation time longer following priming. This might indicate a different mechanism of action than previously thought.

Study design, size, duration
A prospective, paired, non-blinded, single-center study including 20 women conducted between January 2021 and July 2021 at a tertiary referral hospital. Participants underwent two identical IVF treatments: a Control cycle including elective freezing of all blastocysts and a Study cycle with fresh blastocyst transfer. The Control and Study cycles were separated by eight weeks (two menstrual cycles) of hCG-priming by daily injections of 260 IE hCG (details in our previously published paper).

Participants/materials, setting, methods
Women aged 18-40 years with cycle lengths of 23-35 days and AMH &lt;6.29 pmol/L. Control and Study IVF cycles were performed in a fixed GnRH-antagonist protocol. Blood samples were taken on stimulation day 1, stimulation day 5-6, trigger day, day of oocyte pick up (OPU), and trigger day + 7 days in the Control and Study cycles. Follicular fluid was collected from the first aspirated follicle on both sides during OPU in both cycles.

Main results and the role of chance
Inhibin B serum levels were significantly lower on stimulation day 1 after hCG-priming, but no other significant differences in serum Inhibin B or androgen levels were seen. The concentrations of Inhibin B and androstenedione in the follicular fluid from the Study and Control cycle did not vary but testosterone was significantly lower in the Study cycle. A lower Inhibin B in the Study cycle corresponds with the antral follicles being significantly smaller after priming, and this probably led to a longer stimulation time in the Study cycle. This contradicts the theory that androgen priming causes more FSH receptors on developing (antral up to preovulatory) follicles. Instead, we hypothesize that androgen priming rescued some small antral follicles that would have otherwise undergone atresia by the end of the previous menstrual cycle. The mechanism of action was likely an increase in androgen levels and FSH receptor expression within these small follicles, however, not enough to elevate androgen levels in serum. We retrieved significantly more oocytes in the Study cycle and the production of estradiol per follicle ≥10 mm on trigger day was comparable in the Study and Control cycle, suggesting that the rescued follicles were competent in producing oocytes and steroid hormones.

Limitations, reasons for caution
The sample size was small, and androgen and Inhibin B levels were not the primary outcome. We have not demonstrated a higher androgen level or FSH receptor expression in small antral follicles following hCG-priming.

Wider implications of the findings
The results make us question the mechanism of action behind hCG-priming prior to IVF. It is important to design a study with retrieval of small antral follicles immediately after priming to investigate the proposed hypothesis and to confirm improved cycle outcomes i.e., more retrieved oocytes in a larger study population.

Trial registration number
NCT04643925