During a normal monthly reproductive cycle, the endometrial lining of the uterus undergoes a series of changes that make it receptive to the possible arrival and successful implantation of an early-stage embryo. Endometrial receptivity only lasts about 12 hours; under natural conditions it coincides with the time that the early-stage embryo would be expected to arrive at the uterus, if in fact an egg was fertilized that month. It all just happens naturally, without any thought on our part.
For infertile couples who opt for in vitro fertilization (IVF) in an attempt to become pregnant, timing can be critical. If the embryo is introduced into the uterus at a time when the uterus is not receptive, the whole process can end in failure. An IVF procedure can cost tens of thousands of dollars, and its not unheard of for couples to try multiple times without success and without knowing why. One possible reason for multiple failures is that the embryo may not have been introduced into the uterus at precisely the right time. The 12-hour window of maximum receptivity can occur on different days of the cycle in different women, and in the past there was no way to determine it.
But now there's a test to determine the precise moment of maximum endometrial receptivity. It's called the endometrial receptivity array (ERA) test. The test works by analyzing the genetic expression of several hundred of the genes known to be involved in the buildup of the endometrium in preparation for implantation. The period of maximum expression of these genes coincides with the best time for embryo implantation. The test has dramatically improved the odds of a pregnancy for couples who had previously experienced multiple IVF failures.
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