THE INFLUENCE OF SPERM MORPHOLOGY AND THE ACROSOME REACTION ON FERTILIZATION OUTCOME AFTER SUBZONAL INJECTION (SZI) OF HUMAN SPERMATOZOA

The usefulness of sub-zonal injection (SZI) for the treatment of sever e male factor infertility has been restricted by low and unpredictable fertilization rates and the high risk of polyspermy after the injecti on of multiple spermatozoa. In this prospective study, we have evaluat ed whether sperm morphology and the percentage of acrosome-reacted spe rmatozoa at the time of injection can be used to predict SZI fertiliza tion outcomes. Populations of motile spermatozoa equivalent to those i njected were collected from the medium/oil interface immediately after SZI of each cohort of oocytes. Morphology was assessed using the Worl d Health Organization 1987 criteria and the acrosomal status of sperma tozoa was determined after staining with rhodamine-conjugated Pisum sa tivum agglutinin. A fertilization index (FI) was calculated to express the actual fertilizing potential of the spermatozoa injected. In all, 67 patients underwent 72 SZI cycles. The overall fertilization and po lyspermy rates were 36 and 47% respectively, and a clinical pregnancy rate per transfer of 22% was achieved. Linear regression analysis demo nstrated a statistically significant relationship between morphology a nd the FI (r = 0.506, P < 0.0001). Patients with less than or equal to 10% normal morphology always had a FI less than or equal to 10%, and this was reflected by low fertilization and polyspermy rates and the h igh number (32%) of cycles with complete failure of fertilization in t his group. In patients with > 10% normal morphology, there were two pa tterns: low (less than or equal to 10% FI) or high (> 10% FI) fertilit y. This was evident in the fertilization (23 and 85%, respectively) an d polyspermy (25 and 68%, respectively) rates of these two patient sub -groups. While the percentage of acrosome-reacted spermatozoa at the t ime of injection,vas weakly correlated with the FI (r = 0.292, P < 0.0 5), it could not be used to predict differences in fertilization poten tial between patient sub-groups. We conclude that sperm morphology and acrosomal status at the time of injection are of limited use in predi cting SZI fertilization outcomes, although patients with poor morpholo gy (less than or equal to 10% normal) have lower fertilization and pol yspermy rates.