The relationship of semen parameters to fertilization in patients participating in a program of in vitro fertilization.

Approximately 80% of the patients in a program of in vitro fertilization (IVF) will fertilize an oocyte. The purpose of this study was to determine which parameters of the semen analysis influence fertilization in vitro. Of 120 patients participating in an in vitro fertilization program, 98 achieved fertilization of at least one mature oocyte and 22 did not. Ovulation induction was standardized and patients whose sperm was exposed to at least one mature oocyte (by light microscopy) were included in the study. Semen washing was accomplished using a "swim-up" technique. Semen parameters were assessed both before (raw) and after washing. Following insemination with 100,000 motile sperm, fertilization was determined by the presence of pronuclei or cleavage. Mean sperm count and motility were higher in patients who fertilized. However, morphology was similar. Fertilization was more likely to occur with a raw density greater than 104 million/ml and a motility greater than 64%, as well as with a density greater than 18 million/ml and a motility greater than 86% following washing. Furthermore, washing lowered sperm counts by 75% and increased motility by 25% but had no effect on morphology. This study demonstrates that sperm count and motility, but not morphology, influence fertilization in a program of in vitro fertilization and that patients with higher counts and motility have a greater probability of fertilization.