Answer from: Raúl Olivares, MD
The day of the embryo transfer in the frozen embryo cycle depends a lot on whether you are taking hormones or you are in the natural cycle. The idea is that we need to synchronize the age of the embryo, which is usually frozen on day five with the day of the progesterone because a day five embryo should be transferred on the fifth day of progesterone, so the length of the cycle is not so relevant. You can start the progesterone on days 10, 15, or 16 of your cycle. Usually, once the endometrium has reached the right size in the first phase and then the only thing that we do is that the patients start the progesterone, and we transfer the embryo on day five of progesterone to make sure that there is this synchronization between the endometrium and the embryos.
Answer from: Harry Karpouzis, MD, MRCOG, DIUE
What is the indication for a frozen embryo transfer? This can happen because we have frozen embryos because we have done an initial transfer that hadn’t worked and we have some remaining embryos and we need to do a frozen transfer. If we have ovarian stimulation where the hormones, the progesterone goes quite high which is the case, usually, in the polycystic ovaries syndrome, or, sometimes, during endometriosis – we prefer to freeze all the embryos so that we can reduce the chances of hyperstimulation and then proceed with frozen embryo transfer.
Frozen embryo transfer (FET) is nowadays done thanks to the process of vitrification which is an excellent technique that gives us almost equal chances to fresh transfer. It is quite often used, even in our unit. In some cases, we have even better chances of success with frozen rather than fresh embryo transfer.
Regarding the question on which day of the cycle we can do the frozen transfer. This depends on the way that we prepare the endometrium. Frozen embryo transfer can be performed in a natural cycle, a seminatural cycle, or a medicated cycle. Usually, when it is a medicated cycle, we prefer to give a minimum of 12 days or a maximum of 18 days of estrogen before we start giving progesterone. Then, if we have blastocysts, the embryo transfer happens 5 days after the initiation of progesterone. If we have day 3 embryos, the embryo transfer happens 3 days after the initiation of the progesterone.
In total, the embryo transfer happens about 16-20 days after the beginning of the cycle. But, sometimes, we can prepare the lining of the womb in different ways. Sometimes, we need to give an initial injection which is called GnRH analogues. Then, the whole process may last a bit longer. Generally, the timing depends on what way we prepare the endometrium, whether it is a natural cycle or a medicated cycle.
Answer from: Anna Voskuilen, MD
So this depends a bit on the type of preparation cycle we are carrying out on the endometrium. And the type of preparation differs; they can be done with a natural cycle or with a medicated cycle. In a natural cycle, we are going to use the follicles growing in our ovaries and this is going to produce progesterone that is going to make the lining grow as well. Then when we think that everything is accurate, we will trigger the ovulation or wait for it after which we will be able to start the transfer which will depend on the day of the ovulation. If we have a day three embryo, three days after the ovulation we will do the embryo transfer, if we have a day five blastocyst, the transfer will take place five days after the ovulation.
On the other hand, if we do a medicated cycle, we would need hormonal treatment to make the endometrium lining grow as the ovaries are not going to work. When we see that the endometrial lining is correct, we can then start the progesterone and program to have the transfer done 5 days later, 10 days later, or 15 days later. The timings are more flexible in this case because we are not depending on the ovulation of the natural endometrium and this happens normally 3 weeks more or less after starting the menstrual cycle as it will depend on the patient. In some specific cases, we need to put up some preparation beforehand like agonists to inhibit the ovarian function. All these factors depend on and are specific to the case of a patient.
In general, the transfer is done 3 weeks after the menstruation and normally this process lasts 3 weeks. During the treatment, it’s important to note that patients will need to do some check-ups such as an ultrasound and a blood test. Normally between one and three check-ups just to be sure that everything is correct and ready for embryo transfer.
What are indications for frozen embryo transfer when preparing the patient for the procedure?
Two protocols are used in FET cycles. Both include taking hormones, estrogen, and progesterone, to prepare the uterus for implantation. How many days after the period is frozen embryo transfer? What day of the cycle is FET done?