Advanced endometrial maturation after ovulation induction with human menopausal gonadotropin/human chorionic gonadotropin for in vitro fertilization.

Endometrial biopsy was performed between the first and third luteal phase day in 22 normally cycling patients following human menopausal gonadotropin and human chorionic gonadotropin ovulation induction for in vitro fertilization but in whom embryo transfer was not accomplished. Eleven patients showed an "advanced" pattern and 10 an "in-phase" endometrium according to the Noyes criteria. A significant difference in serum progesterone levels on days 16 and 18 was found in these two groups. Serum progesterone levels were significantly higher by day 18 if pregnancy was established. In in vitro fertilization and embryo transfer the embryo arrives 24 to 48 hours earlier than in natural conception in the endometrial cavity. Therefore, the "advanced" endometrium may have some benefit for embryo implantation.