Correlation between quantitative antibody titers of sperm immobilizing antibodies and pregnancy rates by treatments.

Immunological infertility in women who possessed sperm immobilizing (SI) antibodies made it very difficult to conceive using the usual treatments. We examined SI antibodies by the quantitative Sperm Immobilization Test and found the antibody titers (50% sperm immobilization unit: SI50 unit) associated with pregnancy rates. Patients with high SI50 titers (greater than 10 units) did not conceive by ordinary or repeated artificial inseminations with husband's semen (AIH) except when treated with in vitro fertilization (IVF) and embryo replacement. Patients with relatively low SI50 titers (less than 10 units) could conceive either by repeated or ordinary AIH, though the success rates were lower than by IVF-embryo replacement. It is important to assess the SI50 titers by the quantitative method to select treatments for infertile women with SI antibodies. In follow-up studies of the patients who conceived successfully, it was found that SI50 titers tended to decline as pregnancy proceeded.