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 was performe d on 2- to 4-cell stage embryos obtained from in-vitro fertilization ( IVF) patients, We treated 376 embryos from 96 patients with repeated I VF failures (two to four attempts) (group A) and 397 embryos from 111 patients undergoing IVF for the first time (group B). Embryos were tra nsferred immediately after the laser treatment, Both groups were compa red to control groups (A' and B') whose embryos were transferred with intact zona pellucida (ZP). The resulting clinical pregnancies were 41 in A and 44 in B versus 24 in A' and 23 in B' respectively. The pregn ancy rates per patient were 42.7 and 39.6% versus 23.1 and 19% in the control groups (P less than or equal to 0.05), while the implantation rates per embryo were 12.2% in A and 11.8% in B versus 7.3 and 7.1%, T hese results show that laser zona thinning of human embryos at 48 h af ter egg retrieval significantly increases the implantation and pregnan cy rate (P less than or equal to 0.05).