The increasing success of in vitro fertilization (IVF) has come mainly from advances in the way doctors grow and select embryos. When transferred into a woman's womb, however, only a minority of these embryos implant in the lining of the uterus, also known as the endometrium. “The reason,” says Steven L. Young, professor of obstetrics and gynecology at the University of North Carolina at Chapel Hill, “lies primarily with an inability to evaluate if the endometrium is ready for the embryo.” If it is not, embryos will not implant, much like good seed will not grow in bad soil.
Scientists know that the endometrium undergoes dramatic changes during the menstrual cycle and becomes receptive to embryo implantation during only a short period a few days after ovulation. They have yet to find a reliable way to figure out when and if a patient's uterus is ready to accept a hard-won embryo.