Oocyte or embryo number needed to optimize live birth and cumulative live birth rates in mild stimulation IVF cycles

How many oocytes or embryos are needed to optimize the live birth rate (LBR) per cycle and cumulative LBR (CLBR) following mild stimulation IVF (MS-IVF) in women with uncompromised ovarian reserve?

Retrospective analysis of a 4-year database of five fertility centres. The study population included women with normal/high ovarian reserve, who underwent autologous MS-IVF (daily ≤150 IU gonadotrophin) with fresh and subsequent frozen embryo transfer(s) (FET) from surplus embryos. Only the first cycle of each patient was included. Cycles with >150 IU daily average of gonadotrophin were excluded. 'Freeze-all embryo' (FAE) cycles were analysed separately.

A total of 862 consecutive cycles fulfilled the inclusion criteria; 592 were eligible for fresh embryo transfer, 239 had non-elective 'freeze-all' cycles. Median age (25-75th percentile) of women who had fresh embryo transfer was 35 (32-37) years, median antral follicle count 19 (14-28) and anti-Müllerian hormone 19.2 (13-28.9) pmol/l. LBR/fresh cycle and CLBR inclusive of FAE cycles in the <35, 35-37, 38-39 and 40-42 year age groups were 37.8% and 45.1%, 36.0% and 41.6%, 18.4% and 29.1%, and 8.9% and 18.1%, respectively. The LBR following fresh embryo transfer plateaued after nine oocytes (40.3%) or four embryos (40.8%). The CLBR optimized when 12 oocytes (42.9%) or nine embryos (53.8%) were obtained. The LBR per oocyte peaked in women under 35 years when <5 oocytes were retrieved (11.4%), then declined with age and with higher oocyte yield. There were no cases of severe ovarian hyperstimulation syndrome (OHSS).

Nine oocytes, or four embryos, can optimize fresh transfer cycle LBR in MS-IVF. The CLBR are optimized with 12 oocytes, or nine embryos in predicted normal responders, while safeguarding against OHSS.