So called „window of implantation“ (WOI) is a short period of time when the female uterus is capable of accepting a viable embryo for further development, pregnancy. Normally, the endometrium is embryo-receptive around days 19 to 21 of each menstrual cycle. In other days, or in cases of endometrial dysfunction, the female uterus is not ready for pregnancy, and healthy embryos are rejected and die (implantation failure).
As a part of infertility therapy, hormonal treatment can positively modulate the embryo-friendly changes in the female uterus before embryo transfer in IVF cycles. Moreover, the endometrium preparedness can be monitored during each menstrual cycle by ultrasound examination. However, some infertile women still fail to develop pregnancy, despite having high-quality embryos and good-looking endometrium. Endometrial dysfunction (endometrial factor) can be further tested on a molecular level by invasive Endometrial Receptivity Array (ERA test), for which a small piece of uterine mucosa is surgically biopsied and examined for function of several hundreds of genes related to embryo implantation (paid services in specialized laboratories).
In Prague Fertility Centre, asynchronous embryo transfer (ASET) is available for patients with compromised endometrial receptivity confirmed by laboratory, as well as for patients with suspected endometrial factor. The level of endometrial receptivity may vary from cycle to cycle, and the occurrence of implantation window (WOI) may vary as well. Therefore, Prague Fertility Centre can postpone some embryos, so that 2 or 3 embryos of different developmental stages (asynchronous) are transferred. This way, delays in WOI peak or occurrence from 1 to 5 days can be compensated for. Experts in Prague Fertility Centre are ready to assist you in a personalized manner specific for your case.