This systematic review aims to provide up-to-date information on the reproductive, obstetric, and maternal outcomes of the two most commonly used endometrial preparation methods (the natural cycle and the HRT cycle with or without GnRH-a), as well as to discuss any contentious aspects that have arisen in clinics in recent years.
Therefore, it is imperative to have a more scientific basis for FET administration due to the rising number of FET procedures being performed around the world. As a result, some scholars have suggested a “back to nature” approach, advocating for expanded use of natural cycle FET. Īlthough studies showed that FET significantly improves clinical outcomes and allows consecutive embryo transfers, it also has a higher risk of pregnancy-related hypertensive disorders, post-term delivery, macrosomia, and other adverse obstetrical or prenatal outcomes, especially for HRT cycles. However, there is no consensus on the optimal endometrial preparation protocol for FET despite almost four decades since the first successful pregnancy after an FET cycle. Endometrial preparation is a crucial stage in FET cycles, and several protocols are available, including true natural cycle with spontaneous ovulation, modified natural cycle with human chorionic gonadotrophin (hCG) to trigger ovulation, hormone replacement therapy (HRT) cycle with or without gonadotropin-releasing hormone agonist (GnRH-a) downregulation, and ovarian stimulation cycle with or without letrozole.
The use of “freeze-all’’ strategy with subsequent FET is a promising option to reduce the iatrogenic risk of ovarian hyperstimulation syndrome (OHSS), perform pre-implantation genetic testing, avoid embryo-endometrial asynchrony in fresh cycles, and achieve a high live birth rate (LBR) and reliable safety. In recent years, frozen–thawed embryo transfer (FET) technology has become mainstream because of the rapid development of assisted reproductive technology (ART) and the continuous progress of vitrification technology. In addition to improving implantation rates and ensuring the safety of the fetus, addressing these points will allow for individualized endometrial preparation, also as few cycles as possible would be canceled. Currently, there is increasing interest in how the method of endometrial preparation may influence frozen embryo transfer outcomes specifically, especially when it comes to details such as different types of ovulation monitoring and different luteal support in natural cycles, and the ideal exogenous hormone administration route as well as the endocrine monitoring in hormone replacement cycles. Therefore, a ‘back to nature’ approach that advocates an expanded use of natural cycle FET in ovulatory women has been suggested. However, current results suggest that establishing a pregnancy in the absence of a corpus luteum as a result of anovulation may pose significant maternal and fetal risks. Hormone replacement therapy is now used at the discretion of the doctors because it is easy to coordinate the timing of embryo thawing and transfer with the schedules of the in-vitro fertilization lab, the treating doctors, and the patient. Hormone replacement therapy and the natural cycle are two popular methods for preparing the endometrium.
Over the past decade, the application of frozen-thawed embryo transfer treatment cycles has increased substantially.
0 kommentar(er)
