Partial zona dissection enhances the fertilization rate in cases of sperm defect only when total failure has occurred in previous in-vitro fertilization attempts.

The value of partial zona dissection (PZD) was assessed in a randomized protocol of in-vitro fertilization (IVF) including 30 couples (44 cycles) with at least two sperm defects. Couples were divided into three groups according to previous IVF status, i.e. group I: total failure of previous IVF; group II: marginal success of previous IVF, and group III: no previous IVF. Both PZD and untreated oocytes were inseminated using the swim-across method. Although PZD did not enhance the overall proportion of fertilized eggs resulting in diploid cleaving embryos per retrieved oocyte (14.7 versus 17.1%), this rate was higher with PZD than with IVF when previous IVF attempts had failed (group I: 16.1 versus 4.5%, P < 0.01). The rate was similar for PZD and IVF in group II, and lower for PZD than IVF in group III (15.1 versus 30.8%, P < 0.01). The higher polyspermy rate associated with PZD in groups in which classical IVF worked, could partially explain these results. The role of a possible deleterious effect of PZD on the oocytes is discussed. Out of the 44 cycles, 20 reached the embryo transfer stage and four pregnancies were obtained. In our opinion PZD should be carried out in cases of sperm defects only when previous IVF attempts have failed.