Embryo Transfer: Everything You Need to Know

Embryo transfer is the fertilized egg implantation into the womb (uterus). It is integral to the in vitro fertilization (IVF) process. The purpose of an embryo transfer is to assist a person in becoming pregnant. People who have difficulty conceiving may choose to try an embryo transfer as part of assisted reproductive technology (ART).

An embryo transfer is usually performed in a healthcare provider’s office and can result in pregnancy. There are some risks and precautions with the procedure.

This article discusses what to expect before, during, and after an embryo transfer procedure.

What Is an Embryo Transfer?

An embryo transfer is implanting a fertilized egg (embryo) into the uterus. The egg is fertilized in a lab, and once the embryos are ready, a healthcare provider places them in the uterus. If the embryo implants into the uterine wall, pregnancy will occur.

Your healthcare provider may recommend an embryo transfer if you have not been able to conceive naturally. Obstetrician-gynecologists (ob-gyns) with special infertility training usually perform embryo transfers.

When Is an Embryo Transfer Needed?

Most healthcare providers recommend seeking medical help for infertility after trying to conceive for one year. If you are older than 35, see your provider after six months of trying to get pregnant.

An embryo transfer may be a good fit for you if you have certain conditions that prevent you from getting pregnant naturally. The following conditions may cause infertility and could benefit from assisted reproductive technology:

What to Expect Before, During, and After an Embryo Transfer

An embryo transfer is part of the IVF process. During IVF, you will be given fertility medications to stimulate the ovaries to release healthy eggs.

Your healthcare provider will remove the eggs during an egg retrieval procedure. They will then send the eggs to the lab to be fertilized with sperm. Once the eggs multiply, the embryos are ready to be transferred.

The Process of an Embryo Transfer

About two to three days before the scheduled transfer, your healthcare provider will determine which embryos are the most likely to result in pregnancy (most viable). They may perform metabolic profiling to assess the embryos’ health.

Your healthcare provider will likely perform the embryo transfer in an outpatient clinic. The procedure may feel similar to a Pap smear test. Your provider inserts a speculum into the vagina and gently expands it. This keeps the vaginal walls open during the procedure.

Using ultrasound for guidance, your provider will pass a catheter (small tube) through the cervix and into the uterus. They will use the catheter to pass the embryo into the uterus.

An embryo transfer is usually not painful, but the speculum may feel uncomfortable. Most people do not receive anesthesia or pain medications.

After the Transfer

An embryo transfer is an outpatient procedure. Your healthcare provider will tell you when it is safe to sit up and go home. It is expected to feel abdominal cramping or bloating after an embryo transfer. Some vaginal discharge is also considered normal.

Call your healthcare provider if you experience vaginal bleeding after an embryo transfer. They will ask you to return to the clinic in two weeks to determine if the transfer was successful.

Types of Embryo Transfer

There are different types of embryo transfers, and your healthcare provider will recommend one based on the cause of infertility, your age, and your overall health.

Types of embryo transfers include:

• Fresh: Once fertilized, the eggs are cultured for one to two days and transferred.
• Frozen: The frozen embryos are thawed and transferred.
• Blastocyst: Once fertilized, embryos grow for five days until they become blastocysts. They are then transferred. This type of transfer may have a higher success rate than a typical fresh or frozen transfer.
• Assisted hatching: Once fertilized, embryos develop a hard outer layer called the zona pellucida; they must “hatch” from this layer before implanting into the uterine wall. Assisted hatching creates a small break in this outer layer before transferring the embryo.

How Many Embryos Are Transferred?

Your healthcare provider may recommend transferring one or more embryos into the uterus during an embryo transfer. When determining the number of embryos to transfer, they will consider your age, health, and likelihood of becoming pregnant.

A single embryo transfer is usually recommended for healthy people ages 35 and younger. Transferring one embryo reduces the risk of becoming pregnant with multiples (twins, triplets, etc).

People with a higher risk of miscarriage may receive more than one embryo during the transfer. A high-load transfer refers to three or more embryos. Risks of multiples include premature labor, premature birth, and low birth weight.

Success Rates of Embryo Transfers

The success rates for embryo transfers have increased over time. In 2011, the success rate for a singleton birth (one baby) for IVF was 22.7%. In 2020, the success rate was 34.5%.

The percentage of embryo transfers that result in multiple births has decreased. In 2011, 8.4% of people gave birth to twins after IVF. In 2020, the percentage of twins was 2.3%, and the percentage of triplets was 0.05%. This decrease is likely related to the increased use of single embryo transfers.

Several factors impact the success of an embryo transfer, including:

• Embryo health: The most common cause of a failed embryo transfer is a chromosomal abnormality in the embryo.
• Uterine receptivity: This describes how prepared the uterine lining is to accept implantation.
• Parent’s age and reproductive history: An embryo’s risk of chromosomal abnormalities increases as a parent ages.
• Type of transfer: More research is needed to determine whether there is a statistically significant difference between success rates for fresh or frozen embryo transfers.

Risks and Precautions of Embryo Transfers

Embryo transfers and IVF come with risks and are not safe for everyone. The most significant risk is becoming pregnant with multiples. This raises the risk of several pregnancy and birth complications. Fortunately, the risk of multiples from IVF has decreased as healthcare providers have moved toward one embryo transfer, as opposed to several in one transfer.

Possible risks of a pregnancy with multiple fetuses include:

• Prematurity
• Low birth weight
• Small for gestational age
• Cesarean section (C-section)
• Placenta previa (placenta attaches low in the uterus)
• Preeclampsia (high blood pressure in pregnancy)
• Congenital disabilities (structural or functional conditions present at birth)

Possible risks of all types of embryo transfers include:

Summary

An embryo transfer is crucial to the in vitro fertilization (IVF) process. During an embryo transfer, an ob-gyn transfers a fertilized egg (embryo) into a person’s uterus to achieve pregnancy.

Healthcare providers usually perform embryo transfers in outpatient clinics. While the procedure should not feel painful, discomfort is possible. Cramping and bloating after the procedure are normal. It is expected to feel emotional about this procedure. Seek support from your partner, friends, family members, and healthcare providers as often as possible.