Presence of sperm in the perivitelline space predicts fertilization rate after partial zona dissection

Objective To examine the association of the number of spermatozoa present in the perivitelline space and sperm parameters with fertilization after partial zona dissection in male factor patients. Design Partial zona dissection was applied in 62 couples (84 cycles). A total of 524 oocytes underwent partial zona dissection ( 1 8 of the zona circumference) (partial zona dissection group) and 171 sibling oocytes were not manipulated (control group). A total of 326 manipulated oocytes were examined for the presence of spermatozoa in the perivitelline space. Setting University-based in vitro fertilization (IVF) program. Patients Fifty-four (87%) couples had at least one complete failure of fertilization, and 8 (13%) couples had low fertilization rate ( Main Outcome Measures Fertilization rate, cleavage rate, and the number of spermatozoa present in the perivitelline space after partial zona dissection. Results Monospermic and polyspermic fertilization rates were 22.3% and 6.7% in the partial zona dissection oocytes and 8.8% and 0.6% in the nonmanipulated oocytes, respectively. The cleavage rate was similar in the partial zona dissection and control group (69.2% and 66.6%, respectively). A total of 81 partial zona dissection embryos and 10 nonmanipulated embryos were transferred to the uterus of 34 women (39 cycles), resulting in four pregnancies. In 46% (18 of 39) of the patients who had both partial zona dissection and control oocytes, only the manipulated oocytes fertilized. In only 48.8% of partial zona dissection oocytes, spermatozoa were detected in the perivitelline space; in this group of oocytes the fertilization rate was 56.6%. Sperm count and morphology were not clearly correlated with the outcome of partial zona dissection. Conclusions The partial zona dissection technique enhances fertilization of subfertile sperm. However, the low efficiency of the procedure, apart from being associated with a high polyspermic rate, is related to the failure of sperm to traverse the slit in the zona pellucida in approximately one half of the manipulated oocytes.