What is the best way to prepare for frozen embryo transfer?

This review looked at different hormonal methods to prepare the uterus for a frozen embryo transfer (FET). It found that cycles with ovulation led to better outcomes than an artificial cycle.

FET is an infertility treatment in which a frozen embryo is transferred into the uterus. The lining of the uterus needs to be receptive for an embryo to implant. This lining grows and matures in response to hormones throughout the menstrual cycle. It is ready for implantation in the days following ovulation.

There are several methods to prepare the uterus for a FET. A true natural cycle (NC) uses hormone or ultrasound monitoring to time the FET for after a natural ovulation. Modified NC is similar, but uses a trigger injection to prompt ovulation when the follicles containing the eggs are ready. Ovarian stimulation uses fertility medications to stimulate the ovarian follicles to grow and then ovulate. Several different medications can be used. Finally, an artificial cycle uses estrogen and progesterone to prepare the endometrium, without any ovulation.

There has not yet been a large-scale review of different types of FET, and whether one type is more effective.

This review included 139 studies of women using FET. There were 6,372 FET cycles where patients were randomly assigned to one of two types of FET preparation. There were also 105,239 cycles where the method was chosen by patients and their doctors. The researchers used this data to estimate which methods were more effective, even when the studies did not directly compare them.

Aromatase inhibitors (AIs) are a type of fertility medication, and the most common AI is letrozole (Femara). AI cycles had significantly more pregnancies than artificial or true natural cycles. AI cycles also had 67% more births than artificial cycles (ACs). Gonadotropins are another type of ovarian stimulation. Gonadotropin cycles also had 77% more births than ACs.

Modified NCs tended to have more births than ACs, but fewer than ovarian stimulation. However, this could have been due to chance.

Pregnancies following AC had higher rates of several complications than those after NC. These included high blood pressure, heavy bleeding, and preterm birth.

This review found that FETs with ovarian stimulation have higher pregnancy and birth rates than artificial cycles.

AC does not require ovulation. Users of AC more often have health conditions which can affect both ovulation and overall fertility.

Talk to your doctor about whether ovarian stimulation is appropriate for your FET cycle.