The choice of the most appropriate microfertilization technique for human male factor infertility.

Comparisons were made among techniques used to treat male factor infertility. Patients with semen quality below that recognized by World Health Organization criteria as normal had a better success rate when treated by gamete intrafallopian transfer than by in vitro fertilization (25% v. 7% pregnancy rate per patient). When < 2 x 10(6) motile sperm were recovered, the fertilization rate and embryo cleavage rate were higher for microdrop insemination than for conventional insemination. When 7000-370,000 motile sperm were recovered, microdrop insemination resulted in a higher fertilization rate (46%) and a higher incidence of pregnancies (23% of patients treated) than subzonal sperm microinjection (SUSM). However, for patients with 5000-50,000 motile sperm, the immediate transfer of SUSM oocytes to the Fallopian tube increased pregnancy rates for this technique to 24% of patients treated. Direct microinjection of epididymal sperm from azoospermic men into the cytoplasm of oocytes resulted in pronuclear formation in 27% of oocytes; in comparison, pronuclear formation occurred in 5% of SUSM oocytes. These data led to formulation of a logical treatment programme for male factor infertility.