Scientists have tried to predict the best time for a fertilized egg to implant in the uterus by studying the uterus’s genetic makeup, but this hasn’t worked. Instead, it seems that there’s a fairly wide window of time, about two to three days, when the uterus is ready to accept an embryo. A big challenge now is figuring out the best way to prepare the uterus for transferring frozen embryos. Recent research shows that using vaginal progesterone might not be enough for many women, leading to lower success rates and higher risks of miscarriage. Using progesterone injections or a combination of injections and vaginal progesterone seems to be more effective.
