Zona thinning with the use of laser: a new approach to assisted hatching in humans

From 1993 to 1994, in our centre, laser-assisted hatching wasperformed on 2- to 4-cell stage embryos obtained from in-vitrofertilization (TVF) patients. We treated 376 embryos from 96patients with repeated IVF failures (two to four attempts) (groupA) and 397 embryos from 111 patients undergoing IVF for thefirst time (group B). Embryos were transferred immediately afterthe laser treatment. Both groups were compared to control groups(A' and B') whose embryos were transferred with intact zonapellucida (ZP). The resulting clinical pregnancies were 41 inA and 44 in B versus 24 hi A' and 23 in B' respectively. Thepregnancy rates per patient were 42.7 and 39.6% versus 23.1and 19% in the control groups (P < 0.05), while the implantationrates per embryo were 12.2% in A and 11.8% in B versus 13 and7.1%. These results show that laser zona thinning of human embryosat 48 h after egg retrieval significantly increases the implantationand pregnancy rate (P < 0.05).