If you are considering in vitro fertilzation (IVF), you will encounter a lot of new terms. To help you learn the new alphabet of IVF, we will discuss some of these terms. In this blog, we will talk about “embryo transfer,” also known as “ET.”
When you go through IVF, chances are, you and your partner have been trying for some time to conceive naturally without success. With IVF, your fertility specialist will help things along. First, you will take medications to stimulate production of your eggs. After you have produced them, your doctor will retrieve the eggs and enable your partner’s sperm to fertilize them in a laboratory dish. Embryo transfer is when your doctor then transfers the fertilized egg, now called an embryo, from its dish in the lab into your uterus to start a pregnancy.
When does embryo transfer take place during the IVF cycle? After your eggs and your partner’s sperm are combined, some eggs will be fertilized (they take up one sperm each), and these fertilized eggs, or embryos, will develop in the lab over several days. You will probably have your transfer on the third day of development (Day 3), or on the fifth to sixth day (Day 5 to 6) when embryos are expected to develop further to a blastocyst.
Every day is a major milestone at these early stages. On Day 3, the embryo is expected to have eight cells, but this could typically range from five to 10 cells. On Day 5, the embryo is expected to develop to the blastocyst stage, which is special because you can see an inner ball of cells that will form the fetus, and an outer layer of cells that will become the placenta.
Many IVF clinics set up the ET to occur on Day 5 or 6, when embryos reach the blastocyst stage. Some embryos may not make it to the blastocyst stage, and many experts believe the extra two days is a good way to tell which embryos are more likely to develop to produce a pregnancy.
The number of embryos you have may also impact whether to have embryo transfer earlier (say, Day 3) or later (say, Day 5). If you have fewer embryos, there is a small chance that no embryos will survive to Day 5, and that may sometimes lead your doctor to suggest an earlier embryo transfer.
Are there other factors that affect the day of transfer? After your egg retrieval, your fertility doctor will be watching how your body is responding to the ovarian stimulation drugs you had taken to stimulate the production of the eggs. In particular, your doctor will watch for signs of Ovarian Hyperstimulation Syndrome (OHSS), an exaggerated response to your medications which sometimes can lead to cardiovascular complications. In this case, your fertility doctor may postpone embryo transfer for a month for the drug reaction to wear off. Your doctor may suggest freezing the embryos until then for a frozen embryo transfer (FET).
Recent research shows that very high levels of estrogen also aren’t best for a successful pregnancy. In this case, your physician may suggest you freeze the embryos for a frozen embryo transfer a month later.
How many and which embryos should be transferred?
The morning of the embryo transfer, your embryologist give each embryo a score. He or she will look for indicators of quality, such as the number of cells in each embryo, if the cells are of similar size, and whether any embryos have “fragmentation” (or parts that are broken off).The best embryos have even, same-sized cells with little fragmentation.
Your doctor will discuss with you how many embryo(s) and which ones should be transferred. For most patients, it’s probably one to two embryos. But other factors, including your age, the quality of your embryos, the condition of your uterus, or other medical conditions can affect the number that your doctor recommends to give you the best chance of a normal, successful pregnancy.
The American Congress of Obstetricians and Gynecologists (ACOG) reported research results showing that the transfer of a single embryo, especially when pre-screened for genetic abnormalities, leads to more successful pregnancies and births. Univfy has developed the Univfy IVFsingle test, which predicts your chances of having twins based on your medical data, and that can help you and your doctor decide on how many embryos to transfer. This test has been used in some centers, and we will soon make this available on our Website.
What happens during and after the embryo transfer? On the day of the transfer, your doctor may prescribe medication to relax you. You will be asked to have a full bladder to make it easier to see the parts of the uterus with ultrasound to place the embryo correctly.
You will be asked to sit in a gynecological exam chair in the same way as you would for your annual PAP smear. Your doctor will place the embryo(s) inside the uterus with a very tiny sterile plastic tube, or catheter.
Afterwards, you will rest a bit at the clinic, and then go home and avoid strenuous activity for the day. Your doctor will prescribe a hormonal supplement (some form of progesterone, either in an injection format or vaginal suppository) for you to take daily to support early embryo implantation. Then, about two weeks after the transfer, you will get a blood test to determine if you are pregnant. Let’s hope you have a good result!
Check out our blog on frozen embryo transfers, or FET's, for more on the alphabet of IVF.