November is Prematurity Awareness Month, an opportunity to raise awareness about babies born too soon and the steps healthcare providers and families can take to support healthier pregnancies.
A baby is considered preterm when born before 37 weeks of pregnancy. According to the March of Dimes, preterm birth remains a significant maternal and infant health concern in the United States.
There are many reasons a baby may be born prematurely, and some risk factors are outside anyone’s control. One known risk factor is carrying twins, triplets, or other multiples. For families pursuing in vitro fertilization (IVF), this is where a conversation about elective single embryo transfer, commonly called eSET, can become particularly important.
Why Multiple Pregnancies Increase the Risk of Premature Birth
Twins can be wonderful news for families, but medically, a multiple pregnancy carries greater risks than a singleton pregnancy.
More than half of twins and nearly all triplets and higher-order multiples are born prematurely. Babies born early may need additional medical care after delivery, including time in a neonatal intensive care unit (NICU). The earlier a baby is born, the greater the potential for complications involving breathing, feeding, development, and other aspects of health.
Multiple pregnancies can also increase health risks for the person carrying the pregnancy, including a greater likelihood of conditions such as preeclampsia and gestational diabetes.
For people pursuing fertility treatment, reducing the likelihood of a multiple pregnancy whenever medically appropriate can therefore be an important part of planning for a healthy pregnancy.
What Is eSET?
eSET stands for elective single embryo transfer. During this procedure, 1 embryo is selected and transferred to the uterus during an IVF cycle rather than transferring multiple embryos at the same time.
The goal is to achieve a healthy singleton pregnancy while reducing the likelihood of twins or higher-order multiples.
Research examining elective single embryo transfer has helped demonstrate its role in reducing multiple pregnancies associated with assisted reproductive technology.
The American College of Obstetricians and Gynecologists (ACOG) has also emphasized the importance of reducing multifetal pregnancies associated with fertility treatment. ACOG notes that single embryo transfer can achieve strong pregnancy rates while substantially reducing multifetal pregnancies.
Why Has eSET Become More Common?
Years ago, transferring multiple embryos during IVF was more common because fertility specialists hoped that doing so would increase the chance that at least 1 embryo would implant.
IVF has changed considerably since then.
Improvements in embryo culture, blastocyst development, cryopreservation, laboratory practices, and embryo selection have allowed fertility specialists to be more selective about how many embryos they transfer.
Professional recommendations have changed as well.
The Society for Assisted Reproductive Technology (SART) and the American Society for Reproductive Medicine (ASRM) have developed guidance on the number of embryos to transfer to maintain strong pregnancy outcomes while reducing twin and higher-order multiple pregnancies.
Today, patients with a favorable prognosis who are younger than 35 are strongly encouraged to receive a single embryo transfer. For patients ages 35 to 37 with a favorable prognosis, single embryo transfer should also be strongly considered. If an embryo has been determined to be euploid, meaning it has the expected number of chromosomes, current guidance recommends transferring 1 embryo regardless of the patient’s age.
Individual circumstances still matter, so always discuss the number of embryos transferred with a reproductive endocrinologist.
Where Does PGT-A Fit In?
Some patients undergoing IVF may also discuss Preimplantation Genetic Testing for Aneuploidy, or PGT-A, with their fertility specialist.
PGT-A examines cells from an embryo to assess whether it has the expected number of chromosomes. Embryos with an abnormal number of chromosomes are known as aneuploid embryos and are less likely to result in an ongoing healthy pregnancy.
If PGT-A identifies a euploid embryo, transferring a single euploid embryo can help reduce the risk of a multiple pregnancy that would come with transferring more than 1 embryo.
However, PGT-A is not necessary or appropriate for every IVF patient, and it cannot guarantee implantation, pregnancy, or the birth of a healthy baby. Your reproductive endocrinologist can explain the potential benefits and limitations based on factors such as your age, medical history, previous treatment, and number of available embryos.
Families with questions about inherited genetic conditions or donor genetics may also benefit from learning about Seattle Sperm Bank’s genetic testing services and discussing appropriate testing with their fertility care team or a genetic counselor.
Does Transferring 1 Embryo Lower Your Chances of Having a Baby?
It’s easy to understand why someone might think transferring 2 embryos provides twice the opportunity for pregnancy. IVF outcomes are more complicated than that.
For appropriately selected patients, transferring a single embryo can offer a strong chance of pregnancy without accepting the additional risks associated with deliberately transferring multiple embryos.
There is also a difference between looking at the outcome of 1 transfer and considering the cumulative opportunity for pregnancy from an IVF cycle. If additional healthy embryos are available, they can often be frozen and transferred individually in future cycles rather than transferring several at once.
This approach can provide more than 1 opportunity for pregnancy while reducing the likelihood of a multiple gestation with each transfer.
What If I’m Using Donor Sperm?
For intended parents using donor sperm with IVF, the embryo-transfer conversation is generally the same. The number of embryos transferred depends on factors related to the patient, embryos, and treatment plan, not simply whether donor sperm was used.
Donor sperm may be part of IVF for single parents by choice, LGBTQ+ families, couples experiencing male factor infertility, people with certain genetic conditions, and other intended parents.
Seattle Sperm Bank’s family planning resources can help intended parents learn more about donor conception and the considerations that may come with incorporating donor sperm into fertility treatment.
Making an Informed Decision About Embryo Transfer
Every IVF cycle is different, so eSET is a conversation to have with your reproductive endocrinologist, not a decision based solely on age or a general guideline.
Your physician may consider your age, embryo quality, whether PGT-A was performed, previous IVF outcomes, medical history, and other factors before recommending how many embryos to transfer.
Some useful questions to discuss with your fertility team include:
- Am I a good candidate for single embryo transfer?
- How would transferring 1 versus multiple embryos affect my risk of twins?
- What are my individual chances of pregnancy with eSET?
- Would PGT-A be useful in my circumstances?
- If I have additional embryos, can I freeze them for future transfers?
The goal is to make a decision based on your individual circumstances while considering both the chance of pregnancy and the health of the pregnancy that follows.
Supporting Healthy Beginnings
During fertility treatment, it’s natural to focus heavily on achieving pregnancy. Prematurity Awareness Month reminds us that the goal extends beyond a positive pregnancy test.
The hope is a healthy pregnancy, a healthy delivery, and a healthy baby.
For many IVF patients, eSET can help support that goal by reducing one preventable risk factor for premature birth: multiple pregnancy.
If you’re preparing for IVF, talk with your fertility specialist about embryo transfer recommendations, the potential role of genetic testing, and the approach that makes sense for your individual circumstances. Having those conversations before transfer can help you make an informed decision with both your pregnancy and your future family’s health in mind.