Chemical removal of zona pellucida versus laser assisted hatching after repeated failures of assisted reproductive technology.

To evaluate outcomes after zona pellucida removal by pronase or laser assisted hatching in women with repeated assisted reproduction failures. Of 389 procedures (January 2004 to November 2005), 203 control cycles had an intact zona, 116 cycles had chemical removal of the zona and 70 cycles had laser assisted hatching. Rates of pregnancy, implantation and abortion were compared, and pregnancy rate was secondarily evaluated for fresh or frozen-thawed blastocysts. Pregnancy rates were 33.5% (68/203) for controls, 29.3% (34/116) for chemical removal and 30.0% (21/70) for laser. Implantation rates were 24.8% (68/274) for controls, 21.8% (34/156) for chemical removal and 30.0% (21/105) for laser. There were no significant differences among groups. Abortion rates were 15.6% (10/64) for controls, 13.9% (5/36) for chemical removal and 14.3% (3/21) for laser. No difference was observed by blastocyst type for control or laser assisted hatching cycles. In the chemical removal group, both pregnancy and implantation rates were higher for frozen-thawed blastocysts than for fresh blastocysts. (41.5% 13.2% and 30.7% 11.1%, respectively). Assisted hatching did not show a significant benefit. Chemical zona pellucida removal might increase pregnancy rates for frozen-thawed blastocysts. (Reprod Med Biol 2006; 5: 263-267).