Factors affecting pregnancy success of human in-vitro fertilization in unstimulated cycles

Successful pregnancies have recently been reported in cyclesof unstimulated in-vitro fertilization (IVF) which is a simplificationof the standard IVF approach utilizing ovarian stimulation.The purpose of this study was to analyse retrospectively theresults of the first 3 years of unstimulated IVF cycles at ourinstitution in order to identify factors which predispose thesecycles to success or failure. All patients (n= 57) underwentserial monitoring with transvaginal ultrasound and serum oestradioldeterminations. Human chorionic gonadotrophin (HCG) 10 000 IUwas administered when follicles were felt to be mature and aspirationundertaken (n= 98) 34–36 h later. Among nine patientsaged40 years, 13 aspirations resulted in nine embryo transfersand no pregnancies. In one completed cycle in this group, thepatient, who was 42 years old had a baseline follicle stimulatinghormone(FSH) concentration of 35.3 mIU/ml. The cycle progresseduneventfully and follicle aspiration yielded two oocytes andtwo morphologically normal embryos which, however, did not implant.In six patients <40 years with male factor, seven aspirationsyielded 18 oocytes of which 15 were inseminated and did notfertilize. One of the immature oocytes was allowed to maturein vitro and was fertilized and cryopreserved. Its transferin a subsequent cycle yielded a live birth. Among 78 cyclesin 42 patients aged <40 years without male factor, 63 resultedin embryo transfer with 14% clinical pregnancy rates per aspirationand 17% per embryo transfer. Pregnancy was associated with higheroestradiol concentrations at the time of HCG administrationand multiple embryos available for embryo transfer. There wasno effect on the pregnancy rate by the day of HCG administration,follicle diameter, number of cycles completed or number of oocytesobtained. We conclude that unstimulated IVF is a clinicallyviable alternative to stimulated cycles, that patients may beoffered up to three cycles without an appreciable decrease insuccess rates and that success rates which are highest amongwomen < 40 years old and in the absence of male factor maybe maximized by the attainment of maximal oestradiol coneetrationsprior to HCG administration