Endometrial Preparation in Frozen Embryo Transfer Cycles

In order to get optimal pregnancy rates after frozen embryo transfer (FET), the embryo stage and endometrium should be synchronized. Endometrial preparation is done by either natural, artificial (Hormonal replacement therapy HRT) , modified natural methods or mild ovarian stimulation. HRT cycle has a better schedualization however, there are some reports about higher rates of miscarriage, pregnancy induced hypertension (PIH) and preeclampsia (PET) in HRT cycles. A recent study has found that incorporation of the aromatase inhibitor (letrozole) to HRT cycles was associated with better FET outcomes in comparison to hormonal replacement therapy cycles alone. Meanwhile, mild ovarian stimulation protocol can be done either by oral drugs like letrozole or by letrozole plus gonadotropins . So this study aims to compare the reproductive outcomes in two endometrial preparation protocols for frozen embryo transfer cycles; letrozole mild ovarian stimulation versus HRT plus letrozole incorporation.