Partial zona dissection of human oocytes when failure of zona pellucida penetration is anticipated.

Partial zona dissection (PZD) of human oocytes facilitates sperm penetration through mechanically made holes in the zona pellucida. Only 1 of 69 eggs was damaged when sucrose was used to shrink the ooplasm during micromanipulation. The fertilization rate of micromanipulated oocytes in 18 couples with male factor infertility was 68% (34/50), which compared favourably with insemination of non-micromanipulated controls (21/45, 47%). PZD was advantageous in oligozoospermic patients, but not in cases of asthenozoospermia, combined semen problems or immunological infertility. Three twin and two singleton pregnancies resulted following replacement of 23 micromanipulated and eight control embryos in 14 patients. No differences in embryo morphology and development rates were found between the micromanipulated and control groups. The incidence of polyspermy in couples with abnormal semen analyses was relatively low (less than 20%) possibly due to partial activation of the oocytes following exposure to sucrose. Polyspermy was high (57%) in normozoospermic patients with either immunological infertility (n = 3) or failure of fertilization in previous cycles (n = 4). In the three immunological patients, nine of 11 hyaluronidase and sucrose-exposed control embryos fertilized and six implanted, possibly indicating that cumulus and corona cells are contributing factors inhibiting fertilization in such cases.