How to do an FET

In my last blog post I discussed the general concept of frozen embryos which is certainly a bit of a mind bending concept by itself. But I want to emphasize how important the option of having cryopreserved embryos can be to a patient’s overall chances for success. Many times over the years we have ended up with success by using the last frozen embryo that a patient had to work with after multiple failed cycles. Of course, the natural response would be that if we were really smart, then we should have known which embryo out of the whole bunch would go on to make a baby. I agree, but we are not that smart…yet. So until that time we all just have to ride that emotional roller coaster up and down as we try our best to achieve success.

As we head into one of the final weekends of summer let’s discuss the process of setting up an FET and review how do we get those frozen embryos back inside of our patients at the right time in the reproductive cycle. Here is today’s “Question of the Day” from 100 Questions and Answers about Infertility: the book that so many people are having trouble putting down because we coated the outside with superglue.

76. What is the difference between a natural­cycle frozen embryo transfer (FET) and a medicated FET?

There are two possible options for performing a frozen embryo transfer (FET): natural-cycle FET and medicated FET. Natural-cycle FET is available to women with regular ovulation and monthly menstrual cycles. In patients with predictable menstrual cycles, we can carefully monitor the cycle to determine the precise timing of ovulation. Alternatively, ovulation can be induced with the administration of an HCG injection. Once the precise date of ovulation is set, then the uterine lining should be receptive to embryo transfer 5 days later (for embryos frozen on day 3 in a previous IVF cycle). In this way, the embryos can be replaced at approximately the time when they would normally be arriving in the uterus.

One problem with natural-cycle FET is that the optimal time for implantation may fall at an unpredictable time during the laboratory work schedule. In addition, natural-cycle FET demands frequent patient monitoring around the time of ovulation. If a cycle is suboptimal in terms of the estrogen level and endometrial development, then the embryos should not be thawed and the cycle should be canceled.

A medicated FET allows the couple to avoid some of the pitfalls associated with a natural-cycle FET. In this type of FET, estrogen pills, shots, or patches are used to prepare the endometrium for embryo implantation. Three days prior to embryo transfer, the woman begins taking progesterone to modify the endometrial lining so that it will be receptive when the embryos are placed. Some clinics prescribe GnRH agonists (such as Lupron) to their female patients the month prior to a medicated FET cycle so as to reduce the chances of spontaneous ovulation. The use of Lupron reduces the chances of cycle cancellation owing to unexpected ovulation to near zero.