Embryo transfer overview
- Embryo transfer is the step during in vitro fertilization (IVF) treatment in which an embryo (or two, if recommended) is placed in the woman’s uterus.
- A single embryo transfer is sometimes recommended to reduce the risk of multiple pregnancy (twins or more), due to the health risks to mother and child.
- The procedure for embryo transfer is the same whether the embryos were fresh or frozen prior to transfer.
What is an embryo transfer?
Embryo transfer is the placement of an embryo(s) created through IVF into the recipient’s uterus. Embryos may be transferred at an early stage of development when they have few cells (cleavage stage), or in later stages of development when they have many more cells (morula and blastocyst stages).
The age and developmental stage of the embryo is described as Day 1, Day 2, Day 3, Day 4, Day 5 or Day 6 after Day 0, which is the day of egg retrieval. At the LLU Center for Fertility, embryo transfer most often occurs on Day 5 of development when embryos are blastocysts.
In the embryo transfer room at the LLU Center for Fertility, intended parents will be asked if they would like to see their embryos through the microscope prior to embryo transfer. The embryologist will review the development and morphology (appearance) of the embryos and confirm the number of embryos to be transferred before the transfer takes place. The embryologist will also confirm how many of the remaining embryos should be frozen and stored for future use.
Using ultrasound guidance, the physician will insert a small catheter containing the number of embryos designated for transfer through the cervix and into the uterine cavity. The embryo will be in a small droplet of culture medium in the catheter. Once the catheter is positioned in the uterus properly, the embryos are gently injected using a syringe and the catheter is removed.
Preparing for the embryo transfer takes much longer than the actual process, which takes only a few minutes to complete. The procedure does not involve anesthesia and requires only a short quiet time or rest period for recovery afterward.
Fresh embryo vs. frozen embryo transfer
Embryos resulting from IVF treatment can be transferred fresh or frozen for later use. A fresh transfer cycle means that the eggs are removed, fertilized and cultured for several days in the lab and transferred into the uterus during one menstrual cycle.
A frozen embryo transfer cycle means that good quality embryos resulting from a previous egg retrieval cycle are frozen for later use. Frozen embryos can be used during the following menstrual cycle or months (or years) in the future.
Due to improvement in egg and embryo freezing techniques, it is becoming more common to undergo a “freeze all” cycle, meaning that all good quality embryos resulting from an egg retrieval cycle are frozen for later use. This allows the recipient’s uterus and ovaries time to return to a more normal condition following hormonal stimulation and egg retrieval.
How many embryos should be transferred?
The decision of how many embryos to transfer must be made by both the recipient and her fertility doctor, weighing the chances of pregnancy against the chances of a high-risk multiple birth (twins or more). Transferring more than one embryo increases the chance that at least one will result in a pregnancy, but carries more risk.
Elective single embryo transfer (eSET) is when the couple decides to transfer only one embryo, even though they have others that could be transferred also. Many fertility doctors recommend eSET for patient’s that have the highest chance of becoming pregnant on their first embryo transfer cycle.
The transfer of two embryos in certain categories of women under 35 years old results in about 30 percent of deliveries being twins. The transfer of more than two embryos in these women results in the delivery of triplets or higher in about 3 percent of cases. Most physicians consider these rates of multiple pregnancy in IVF to be unacceptable, due to the accompanying health risks.
According to the American Society for Reproductive Medicine (ASRM) recommendations for the number of embryos transferred, several factors must be considered including:
- Age and medical history of the woman, including previous IVF treatment
- Developmental stage of the embryos at transfer
- Quality and quantity of the embryos available for transfer
A single embryo transfer is recommended for women who:
- Are under the age of 35 with no previous attempts at IVF or previous successful IVF cycle
- Have good embryo quality and excess embryos available for embryo cryopreservation
In donor egg cycles, the age of the donor should be used to determine the number of embryos to transfer.
A discussion with your fertility doctor will help you decide whether more than one embryo should be transferred in your case.
Risks of embryo transfer
The largest risk of an embryo transfer is the possibility of conceiving twins due to the transfer of multiple embryos. Twins, triplets or more in a pregnancy increase the health risks with each additional fetus. These additional health risks for mothers and babies include:
- Premature birth problems for the child, including
- Lung, stomach and bowel problems
- Nervous system and developmental problems
- Mental retardation
- Health problems for the mother, such as
- Greater risk of pregnancy and delivery complications
- Dangerously high blood pressure
- Gestational diabetes
- Problematic bleeding before and after delivery
The embryo transfer procedure is fairly risk free, but can be associated with:
- Uterine cramping during or after the procedure
- Failed implantation
- Embryo implantation outside of the uterus (ectopic pregnancy)