Sperm immobilizing antibodies often interfere with the penetration of sperm through the cervical mucus. However, the relationship between sperm immobilizing antibody titer and the result of the post-coital test (PCT) has not yet been clarified. The aim of this study was to investigate whether the 50% sperm immobilization unit (SI50) titer, a quantitative measure of sperm immobilizing antibody, in patients’ sera was correlated with the result of PCT.
Method of study
The sperm immobilization test (SIT) was performed for 2834 infertile women in two university hospitals. The SI50 titers were evaluated by quantitative SIT. In some cases with sperm immobilizing antibody, PCT was carried out before ovulation and assessed according to the criteria of World Health Organization (1992). Infertile couples with abnormal semen characteristics were excluded.
Seventy-four of 2834 women had sperm immobilizing antibodies in their sera, giving a positive rate of 2.6%. Twenty-four (77.4%) of 31 women with sperm immobilizing antibodies and 28 (20.4%) of 137 women without the antibody had abnormal PCT results. There was a significant difference between the two groups (P < 0.0001). When patients with sperm immobilizing antibodies were divided into two groups according to the SI50 titers, the abnormal result of PCT was obtained in all 10 patients with high (>10) SI50 titers, while that was 14 (66.7%) in 21 patients with low (10) SI50 titers. There was a significant difference between the two groups (P = 0.04).
The SI50 titer in the serum can predict inhibitory effects on sperm migration through cervical mucus in immunologically infertile women. Evaluation of the SI50 titers in patients’ sera seems to be useful for decision-making in infertile women with sperm immobilizing antibodies regarding whether they have the possibility of conceiving by timed intercourse.