How Single Embryo Transfer Reduces the Risk of Twins in IVF

When many people think of IVF, they imagine adorable twins as a potential outcome. I can’t tell you how often I hear patients express excitement about the possibility of having “two for one” during their fertility treatment. But the reality is that twins, while certainly a blessing, come with significant risks. That’s why at my clinic, we prioritize single embryo transfer (SET) whenever possible, focusing on giving our patients the best chance of a healthy pregnancy and baby, while minimizing complications.

Early on in IVF’s history, transferring multiple embryos was standard practice. The goal was to improve the odds of success, but this approach led to a surge in twin and even triplet pregnancies. Over the years, we’ve learned a lot about the risks that come with carrying multiples, like preterm labor, gestational diabetes, and the need for C-sections. Those are risks that we take very seriously, and it’s why I am a very vocal proponent of one embryo, one baby, one at a time.

The good news is that modern advances in reproductive technology mean we can now transfer a single, high-quality embryo and still achieve excellent success rates, without the increased risk of a twin pregnancy. My name is Dr. Lucky Sekhon and as a practicing REI I help hundreds of patients each year go through IVF, the vast majority of which are single embryo transfers. In this blog, I’m going to dive into why this shift is to single embryo transfer so important, the specific risks associated with twin pregnancies, and how single embryo transfer has helped make IVF safer for patients.

IVF Twin Rates: Then and Now

To give you an idea of how much things have changed, here’s a quick look at the numbers:

Time Period	Twin Births from IVF (%)	% of Cycles Using Multiple Embryo Transfer
Early 2000s	20-30%	80-90%
2020s	5-10%	30-40%

Why Carrying Twins Isn’t Glamorous, It’s Dangerous

There’s something about twins that captures people’s imagination, and I totally understand why—twins are adorable! But we also have to balance that excitement with the reality of what it means for a woman’s body to carry two babies at once. Twin pregnancies, while possible, are much riskier than singleton pregnancies, both for the mother and the babies. Here’s why:

1. Preterm Labor and Low Birth Weight

Carrying twins increases the likelihood of preterm labor significantly. More than half of all twin pregnancies end in premature birth, meaning the babies are born before 37 weeks. This can lead to long NICU stays, respiratory issues, and developmental delays. The earlier the babies are born, the higher the risk of complications. Preterm birth is a major reason why reducing the likelihood of twins is so crucial in IVF.

2. Preeclampsia and Gestational Diabetes

Both of these pregnancy complications are more common in twin pregnancies. Preeclampsia is a dangerous condition characterized by high blood pressure that can lead to serious problems for both the mother and babies if left untreated. The risk of developing gestational diabetes also doubles when carrying twins. This can lead to larger babies, increased chances of C-section, and long-term health risks for both mother and child.

3. Increased Likelihood of C-Section

Another important consideration is that most twin pregnancies result in a C-section delivery. While C-sections are common and generally safe, they do come with a longer recovery time, potential for complications like infection, and a more difficult postpartum recovery.

To put this into perspective, here’s a look at some of the risks associated with twin pregnancies:

Risk	Twin Pregnancy (%)	Singleton Pregnancy (%)
Preterm Birth	60%	10%
Preeclampsia	10-20%	5-8%
Gestational Diabetes	15-20%	8%
Cesarean Delivery	75%	30%

While these numbers can seem alarming, it’s important to remember that they’re also very avoidable. By embracing SET, we’ve seen a major drop in these complications, helping patients experience smoother, healthier pregnancies.

The Game-Changing Shift to Single Embryo Transfer (SET)

One of the most important changes in modern IVF is the transition to single embryo transfer (SET). We now know that transferring just one embryo, rather than two or more, gives our patients the best chance of a healthy pregnancy with a much lower risk of twins.

The beauty of SET is that we’re still able to create multiple embryos during an IVF cycle, but only transfer one at a time. This not only reduces the risk of twins but gives you flexibility for future pregnancy attempts. After we transfer one high-quality embryo, the remaining embryos can be frozen and stored for future use, allowing us to attempt more IVF cycles without the need for additional egg retrievals.

Improved Success Rates with SET

Many patients worry that transferring just one embryo will lower their chances of getting pregnant. The reality is that modern IVF techniques, like extended culture to the blastocyst stage and preimplantation genetic testing (PGT), have dramatically improved the quality of embryos we transfer. This means that SET can achieve nearly identical success rates to transferring two embryos, without the added risks of a twin pregnancy.

Here’s a quick look at how single embryo transfer compares to double embryo transfer in success rates and twinning rates:

Type of Transfer	Success Rate (%)	Twin Rate (%)
Single Embryo Transfer	50-60%	<5%
Double Embryo Transfer	55-65%	20-30%

As you can see, the success rates with single embryo transfer are very close to those of double embryo transfer, but the risk of twins is dramatically lower. To see how far IVF has come, in the 1980s the documented success rate of a single embryo transfer was 20% and up to 40% with the the transfer of four embryos!

Why Modern IVF is Safer Thanks to Single Embryo Transfer

For me, the most important part of fertility treatment is helping my patients build their families safely. That’s why I’m such a big advocate for SET—it’s not just about getting pregnant, but about ensuring a healthy outcome for both mother and baby. Here are a few reasons why I believe SET is a game-changer:

Fewer Complications, Healthier Pregnancies

By reducing the risk of twin pregnancies, we’re able to avoid many of the complications that come with carrying multiples. Fewer preterm births, lower rates of preeclampsia and gestational diabetes, and a much lower likelihood of a C-section all mean a healthier and safer pregnancy journey.

Flexibility with Frozen Embryos

One of the great things about SET is that you can still have multiple chances at pregnancy. If the first embryo transfer doesn’t result in a pregnancy, we can try again with one of your frozen embryos without the need for another full IVF cycle. This flexibility can make the IVF process less stressful and more manageable, both emotionally and financially.

Conclusion

While the idea of twins can seem exciting, it’s important to understand the risks involved in carrying more than one baby at a time. Thanks to advancements in IVF technology, we can now offer the best of both worlds: a high chance of a successful pregnancy with a much lower risk of twins. If you’re considering IVF, I encourage you to talk to your doctor about the benefits of SET and how it can help you achieve a healthy pregnancy outcome.

At my clinic and most of those in the country, SET has become the go-to approach, and we’ve seen firsthand how it leads to healthier pregnancies and safer outcomes for patients. The goal isn’t just to get you pregnant—it’s to help you bring home a healthy baby.

If you’d like to learn more about how IVF works, please checkout some related blog posts here. If you stumbled onto this page and found this article useful, please follow me on Instagram where I regularly post content regarding IVF, fertility and reproductive health.

If you are considering IVF or suffering from infertility and are interested in booking a consultation with me at my New York City office, you can submit an appointment request here.

References

Sullivan-Pyke C, Senapati S, Mainigi M, Dokras A (2017). “Single versus double embryo transfer: The great debate.” Fertility and Sterility, 108(5): 806–813.

Centers for Disease Control and Prevention (CDC) (2021). “Assisted Reproductive Technology (ART) Report.”

European Society of Human Reproduction and Embryology (ESHRE) (2020). “ESHRE 2020 ART fact sheet.”

Murray, S., et al. (2020). “Trends in multiple births conceived using assisted reproductive technology, United States, 2017–2018.” Journal of the American Medical Association (JAMA). SART (Society for Assisted Reproductive Technology). “National Summary Report.”