Fresh and Frozen Embryo Transfers

The goal of this SART micro-video is to explain to explain fresh and frozen embryo transfer.

Hello my name is Brook Rossi and I am a practicing reproductive endocrinologist and infertility specialist in Columbus, Ohio.

Many IVF patients have heard or read about the differences between fresh and frozen embryo transfers. The goal of this SART micro-video is to explain fresh and frozen embryo transfers.

As you may know an IVF cycle involves the stimulation of the ovaries and the collection of eggs in an egg retrieval. The eggs are then fertilized and embryos are created in the laboratory. With a fresh embryo transfer, the embryo transfer is performed usually either three or five days after the retrieval. In a frozen embryo transfer cycle, the embryo has been previously created, sometimes even years earlier, and then will be placed into the uterus.

With either a fresh or frozen transfer the endometrium or lining of the uterus needs to be prepared so that the embryo can more easily implant. The endometrium is usually checked with an ultrasound to see if it has an appropriate thickness and quality. With a fresh transfer the estrogen made by the ovarian follicles helps to prepare the endometrium. With a frozen transfer, patients may use estrogen patches, pills, or shots to help the endometrium. Sometimes patients may not use any medications.

Frozen embryo transfers are very common. There are several reasons why a patient may choose or be encouraged by their IVF clinician to consider a frozen embryo transfer. One of the most common reasons for a frozen embryo transfer is that the patient has leftover embryos from a fresh cycle. If a patient doesn't get pregnant, has a pregnancy loss, or has had a baby but would like another, they can use the extra embryos that have been previously created. We've learned over the years that there may be other factors that may lower the chance of getting pregnant with a fresh transfer, thus making a frozen transfer a good option. These factors may include concern for worsening ovarian hyperstimulation syndrome if a patient conceives with a fresh transfer, elevation of progesterone during ovarian stimulation, leading to concern that the embryo and the uterus are out of sync. Patients planning genetic testing of the embryos usually need to freeze the embryos while waiting for test results. Finally, if there is an issue with the endometrium, such as a polyp or a thin endometrium, the transfer may be cancelled until the uterus can be evaluated completely.

In general, the chance of getting pregnant with a fresh or frozen embryo may be the same. Also the technology used to freeze and thaw embryos has advanced such that the likelihood of the embryo surviving the process is very high. So this has led many people to wonder which is better fresh or frozen. Should we be doing one or the other for all patients?

One of the most helpful studies to answer this question was recently conducted, in fact it used the SART database, which includes most IVF cycles done in the United States. It was a large study of over eighty thousand IVF cycles. They looked at pregnancy rates and the chance of having a baby between women having fresh and frozen embryo transfers. One of the interesting parts of the study was that they looked at different types of patients. Women who were high responders had or more eggs retrieved while intermediate responders had six to fourteen eggs retrieved. If a woman had to eggs retrieved, she was considered a low responder. High responders had a higher chance of pregnancy and live birth with a frozen cycle. If women had less than eggs retrieved, she was more likely to have a pregnancy or baby with a fresh transfer.

An important consideration is, are pregnancies or babies made from these types of transfers different? Some studies have demonstrated that pregnancies from a frozen embryo transfer are less likely to be an ectopic pregnancy or result in a preterm delivery. Also, the babies seem to be less likely to have low birth weight or be small for gestational age. Some people speculate that the differences seen between fresh and frozen transfers is related to the fact that the woman's hormonal environment is very different in a fresh IVF cycle due to the ovarian stimulation. In a frozen cycle, the hormonal environment may be more physiologically similar to a pregnancy conceived without any infertility treatment. So the pregnancy outcomes may be more likely to be normal.

Large studies are still evaluating which type of transfer is better. Some of the more recent studies indicate that one size may not fit all. What is right for each patient may depend on a variety of factors that may arise before or during their IVF cycle. We encourage patients to discuss fresh and frozen embryo transfers with their IVF clinician during the IVF consult. They may have a good understanding of the differences and which may be best for them.

Thank you for your attention and we hope you enjoyed the SART micro-video. 

Reference

Acharya KS et al. Freezing of all embryos in in vitro ferilization is beneficial in high responders, but not intermediate and low responders: an analysis of 82,935 cycles from the Society for Assisted Reproductive Technology registry. Fertil Steril. 2018 Oct;110(5):880-887.