What Is Embryo Transfer, and How Is It Performed?
Dr. Kushnir explains embryo transfer and how the CHR will maximize your chances of success.
Speaker: Dr. Vitaly A. Kushnir
What is embryo transfer?
The embryo transfer is performed in a procedure room that’s adjacent to the embryology lab, and the embryologist loads the catheter with the embryos in a very specific way. The idea is to transfer the embryos as quickly as possible to the patient’s body to minimize the amount of time that they spend outside the of the incubator. We really like to keep the embryos either in the incubator or in the patient’s body as long as possible as that’s their preferred location. Therefore, we get set up to do the procedure before they even take out the embryos from the incubator. From the patient’s perspective, it’s very similar to an insemination or a pap smear (if they’ve never had an insemination). We do use ultrasound guidance to be able to see where exactly in the uterus we are placing the embryos to be able to get them into the ideal location. Embryos are usually transferred at time of cleavage, which is day two or three after fertilization, or at blastocyst stage, which is day five or six after fertilization. The most common days are day three and day five.
How do patients decide how many embryos to transfer?
The number of embryos to transfer depends on the number that is available, but also on the age of patient and the quality of those embryos. We follow the guidelines that are established by the American Society of Reproductive Medicine to help us determine how many embryos to recommend for each individual patient to transfer. That information, in conjunction with their past history and the quality of the embryos, is used to come up with a plan, together with the patient, as to how many embryos we transfer to maximize the chance of pregnancy while keeping the risk of multiples to a minimum. In general, the older the patient, the more embryos it is recommended to transfer. For example, for someone who is in their 20s, we would transfer one or two embryos, depending on the patient’s risk tolerance for twins, whereas in a patient who is over 42, we can transfer as many as five cleavage-stage embryos or three blastocyst embryos. The primary reason for transferring more embryos is that the majority of embryos in older women are of lower quality and are genetically abnormal and will not implant. So we are allowed to transfer more embryos in older women because the chance of pregnancy with those embryos is lower, and even if several embryos implant, the chance that all of them continue to past the first trimester is fairly low because the miscarriage rates are fairly high for each individual embryo. That is the main reason we can transfer more embryos in older women.
How does CHR try to maximize a patient’s chance of reaching embryo transfer?
There are multiple reasons why somebody may not reach embryo transfer. The first is that very few oocytes are retrieved, or that the oocytes that are retrieved fail to fertilize. So it’s important to figure out and maximize the stimulation pattern before you even reach the egg retrieval to get as many eggs as possible. The technique that is used to retrieve the eggs is important and the technique that is used to fertilize those eggs is important to try to maximize the number of available embryos.
What we are seeing increasingly now is the push in our field to culture embryos longer to blastocyst stage in more and more patients, and while this may be a very good strategy in younger women, we think that in women who are older or have lower ovarian reserve and produce fewer embryos, this strategy may actually result in fewer available embryos to transfer if you go to blastocyst stage. And so we’ve seen a number of patients coming from other centers where they’ve attempted to culture a small number of embryos to blastocyst, and those embryos never made it to blastocyst and essentially degenerated in culture, and the patients ended up with no transfer. The American Society of Reproductive Medicine, which is our national professional organization, recognizes this and recently put out an opinion piece saying that culturing embryos to blastocyst stage in women who are older or are poor responders can result in no embryos available for transfer.
What are some of the treatment modalities to maximize the number of embryos available for transfer?
The main points here are that we need to maximize the number of mature eggs so the way that the patient is stimulated before they even reach retrieval is very important. We need to make sure that as many of those eggs as possible that are retrieved are fertilized, so we need to make sure that the fertilization is performed with the appropriate modality, and in many patients this means intracytoplasmic sperm injection (or ICSI). And then we need to ensure that we don’t culture the embryos too long, because in the end even, though we’ve got much, much better at culturing embryos to blastocyst stage, our culture techniques are still not as good as the patient’s uterus. So the plan is to transfer those embryos earlier rather than later, particularly in women who have fewer embryos to work with.
- Embryo transfer is performed under ultrasound guidance, and feels almost like intrauterine insemination.
- At CHR, patients decide how many embryos to transfer. Our physicians and embryologists will help them make an informed decision.
- Ovarian stimulation protocols, egg retrieval techniques, and fertilization and embryo culture techniques need to be individualized to maximize the number of good-quality embryos for transfer.
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