This study is being done in women with endometriosis who are undergoing IVF/ICSI, which are fertility treatments using eggs, sperm, and embryos outside the body. The treatment being studied is letrozole, a medicine taken by mouth during ovarian stimulation, the part of treatment when the ovaries are helped to produce eggs. The purpose of the study is to find out whether adding letrozole during this part of treatment can improve the chance of a live birth after embryo transfer.

In the study, one group receives letrozole together with the usual fertility treatment, while the other group receives the usual treatment without letrozole. Treatment is given during one egg collection cycle, and any embryos made from that cycle may be transferred fresh or frozen and used later within about one year. The study then follows the pregnancy outcomes after these embryo transfers. The study also looks at related conditions such as adenomyosis, a condition in which tissue similar to the lining of the womb grows into the womb muscle.

The study is designed to see whether letrozole can improve reproductive results in this setting and to collect information on pregnancy, birth, and any problems that may happen during pregnancy. It also records pain after egg collection and quality of life around the time of embryo transfer.