Experience with zona drilling and zona cutting to improve fertilization rates of human oocytes in vitro

Zona drilling (ZD) and zona cutting (ZC) were used in an IVF programme to assist fertilization in semen defect patients. Twenty-seven patients consented to ZD where acidified Tyrode's was used to create a hole in the zona pellucida. In 19 patients, ZD increased the fertilization rate to 29% compared with 8% (P less than 0.001) in their routine IVF cycles, and in eight patients precluded from routine IVF, a fertilization rate of 14% was achieved. Twenty-two patients consented to ZC where a slit in the zona is made mechanically. In 12 patients ZC increased the fertilization rate to 31% compared with 14% (P less than 0.01) from previous routine IVF cycles, and in 10 patients precluded from routine IVF, a fertilization rate of 34% was achieved. In 13 cycles, 68 uncut control oocytes were inseminated. In five cycles both control and ZC oocytes were fertilized (n.s.d.). In eight cycles no control oocytes were fertilized compared with 27% of ZC oocytes. The polyspermy rate was 4.6%. Twenty-four per cent of ZD and 12% of ZC (P less than 0.01) oocytes and embryos were degenerate after 42 h. Both ZD and ZC can increase the fertilization rate of sub-optimal semen, however, in our hands neither technique produced a pregnancy.