The length of the follicular phase influences normal fertilization rates in assisted reproduction.

Factors affecting normal fertilization rates (NFR) were studied in 1,776 IVF patients having 3383 treatments during 1990-1992. Interestingly, the longer the follicular phase (LFP) the higher the fertilization rate: LFP <12, 12, 13, and >13 days, NFR 49.6%, 53.8, 53.9 and 56.1% respectively. Higher fertilization rates were also related to normal semen analysis results, older females, the use of frozen husband and donor sperm, the diagnosis of tubal disease and the use of ovarian stimulation protocols other than clomiphene citrate plus human menopausal gonadotrophin.