A type of fertility technique that improves the ability of some embryos to implant during in vitro fertilization; also known as assisted zona hatching. In assisted hatching, a small opening is created in the thick, transparent outer membrane (zona pellucida) of the embryo, increasing the chance that the membrane will be shed and implantation of the embryo in the uterus will occur. In the procedure, an embryo is placed in a petri dish and the membrane is dissolved with a chemical. The embryo is then placed in an incubator and transferred to the woman’s uterus a few hours later. The technique is generally used by couples whose previous attempts at assisted reproductive technology inexplicably failed or whose fertility is limited by advancing age.