Study question: What is the association between the number of oocytes retrieved and the live birth rate (LBR) following first IVF treatment cycles in China?
Summary answer: In first IVF treatment cycles, the LBR after fresh transfer was maximal in the groups with 6-10 or 11-15 oocytes and reduced in the groups with 0-5 or >15 oocytes. Despite this, the cumulative LBR after including frozen embryo transfer cycles increased with an ovarian response.
What is known already: There is a strong association between oocyte number and IVF outcome; however, this is a comprehensive analysis conducted to investigate the relationship between oocyte number and fresh cycle as well as cumulative LBRs in first IVF treatment cycles.
Study design, size and duration: This is a large retrospective cohort study (n = 2455); patients were categorized into four groups according to the number of oocytes retrieved (0-5, 6-10, 11-15 and >15 oocytes). The fresh embryo transfer LBR and cumulative LBR were evaluated by group. Univariate analysis was performed to identify factors that predict the chance of LBR. Multivariate logistic regression was used to assess the association between oocyte number and LBR after adjusting for confounding factors that were identified as significant in the univariate analysis.
Participants/materials, setting and methods: A total of 2455 women who were undergoing their first IVF treatment cycle at the Reproductive Medicine Center of Anhui Provincial Hospital, P.R. China from April 2007 to December 2011 were identified and reviewed. All patients had normal menstrual cycles and were stimulated with a long GnRH agonist protocol. Associations between oocyte number and LBR and miscarriage rate as well as the rate of moderate-severe ovarian hyperstimulation syndrome (OHSS) were analyzed.
Main results and role of chance: The fresh embryo LBR per started cycle increased with the number of retrieved oocytes up to Groups 2 and 3 (6-10 and 11-15 oocytes) and then decreased, because of the high number of cycles with all embryos being cryopreserved, in order to avoid moderate-severe OHSS in group 4 (>15 oocytes). However, the cumulative LBR per started cycle continued to increase with oocyte number, as did the incidence of moderate-severe OHSS. There was no significant difference in the miscarriage rates among the patient groups.
Limitations, reasons for caution: As a retrospective study, our analysis depends on previously recorded data; therefore, certain variables could not be collected. Our findings may be influenced by our young and thin patient population and the inability to control for certain markers of ovarian reserve such as historical maximum serum FSH, antral follicle count and serum anti-Mullerian hormone.
Wider implications of the findings: Our data suggest that in IVF cycles stimulated with a long protocol, the optimal number of oocytes for achieving a live birth is somewhere between 6 and 15. The balance between maximum treatment success and minimum risk of complications, especially OHSS, should be further investigated.
Study funding/competing interests: This study was supported by the Medical Scientific Research Plan Project of Anhui Provincial Department of Health (13ZC014) and the Natural Science Foundation of Anhui Higher Education Institutions (KJ2013Z132).
Keywords: in vitro fertilization; live birth rate; oocytes number; optimum; ovarian stimulation.