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Presence of sperm in the perivitelline space predicts fertilization rate after partial zona dissection
J Levron1, D W Stein, J M Brandes
1Department of Obstetrics and Gynecology, Rambam Medical Center, Haifa, Israel.
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 (< 10%) in previous routine IVF attempts.
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.