Single Embryo Transfer vs. Multiple Embryo Transfer - Trends, Risks, and Why Most Clinics Now Recommend SET

Suggested meta description: Single Embryo Transfer vs. Multiple Embryo Transfer in IVF and surrogacy: what the latest research, ASRM and ESHRE guidelines, and country regulations actually say, and what it means for your journey.

If you are planning a surrogacy journey, sooner or later you will be asked a question that sounds simple but is anything but: how many embryos do you want to transfer?

For some intended parents, this question is barely discussed. The clinic recommends one, the recommendation is accepted, and the cycle moves forward. For others, especially those who have been through multiple unsuccessful attempts, or who feel financial and emotional pressure to "get it right" the first time, the conversation can get complicated very quickly.

I see this often.

And I see how easily this decision gets influenced by things that have nothing to do with what is actually best for the surrogate, the baby, or the family being built. Cost. Time. Hope. The way a clinic frames "your chances." How comfortable you are saying no to something that sounds reasonable on the surface.

This is one of the most important medical decisions in your entire surrogacy journey. It deserves more than a quick recommendation in a consultation.

So let me walk you through it the way I would in a Surrogacy Insider discovery session.

What SET and MET Actually Mean

Single Embryo Transfer (SET) is exactly what it sounds like: one embryo is transferred to the uterus of the surrogate during a single cycle.

When that decision is made even though more than one embryo is available for transfer, it is called elective Single Embryo Transfer (eSET). The word "elective" is important here. It means you and your clinical team chose SET as a strategy, not because it was the only option but because it was the safer one.

Multiple Embryo Transfer (MET), most commonly Double Embryo Transfer (DET), is when two or more embryos are transferred in the same cycle.

That is the technical part. The decision behind which one to choose is where most of the complexity lives.

A Short History of How We Got Here

In the early years of IVF, success rates were low. Implantation per embryo was somewhere between 10 and 30 percent. To compensate, clinics transferred multiple embryos at once - sometimes three, four, or even more.

The result was predictable.

Multiple pregnancy rates exploded. At the peak of the early IVF era, up to 30 percent of ART pregnancies were multiples. Compared to a natural baseline multiple birth rate of around 2 to 3 percent, that was an extraordinary shift, and not the kind of shift anyone would have chosen if the risks had been fully on the table.

Over the past two decades, the picture has changed dramatically.

Better laboratory techniques.

Blastocyst-stage culture.

Vitrification (modern embryo freezing).

And, more recently, preimplantation genetic testing. 

All of this means that today, a single high-quality embryo has a far better chance of resulting in a live birth than several lower-quality embryos did twenty years ago.

The result has been one of the clearest trends in reproductive medicine.

In the United States, the proportion of single embryo transfers rose from 5.7 percent in 2000 to 64.2 percent by 2017. Over that same period, the percentage of multiple births among ART-conceived infants fell from 53.1 percent to 26.4 percent. In Europe, the average multiple birth rate after ART is now around 12 percent, still well above the natural rate, but a significant reduction from where it once was.

In the UK, this shift has gone further. According to the Human Fertilisation and Embryology Authority (HFEA), a typical IVF patient today will have a single fresh embryo transferred in their first treatment cycle, with additional embryos of suitable quality stored for use in subsequent cycles.

Why Multiple Embryo Transfer Carries Real Risks

This is the part that often gets summarised too briefly. So I want to slow down here.

When two embryos are transferred and both implant, the result is a twin pregnancy. To many intended parents, especially those who have waited years for a child, that can sound like a bonus - two babies in one journey. I understand why.

But a twin pregnancy is not simply "two singletons at once." It is a fundamentally higher-risk pregnancy for both the surrogate and the babies.

The data on this is unambiguous.

According to HFEA figures, about 60 percent of IVF twin births are preterm (under 37 weeks), compared to about 9 percent of singleton IVF births. Very preterm births, under 32 weeks, when serious complications are most likely, account for nearly 10 percent of IVF twin births compared to 2 percent for singletons.

The downstream picture is consistent with that.

Compared to singletons, twins are around four times more likely to die in pregnancy, seven times more likely to die shortly after birth, ten times more likely to be admitted to neonatal special care, and around six times more likely to develop cerebral palsy. A pooled European analysis puts the relative risk of very preterm birth (under 32 weeks) in multiple pregnancies at 11.7 times that of singletons (95% CI: 11.1–12.4). 

For the surrogate, the risks are also significantly elevated. Multiple pregnancies can be associated with higher rates of:

• Pre-eclampsia and gestational hypertension

• Gestational diabetes

• Anaemia and postpartum haemorrhage

• Placental complications, including placenta previa and abruption

• Cesarean section, approximately 75 percent of twin pregnancies are delivered by C-section

• Longer NICU stays for the babies, which extends the family's emotional and financial commitment well past delivery

This is not a small list. And in the context of surrogacy, it matters even more, because the person taking these risks is not the parent. It is a woman who has agreed to carry your child on the assumption that her health will be protected by every reasonable medical decision available.

Why Surrogacy Changes the Calculus

This is where the conversation needs to shift specifically toward gestational carrier journeys, because the considerations are not the same as in standard IVF.

A few things to understand.

First, the embryos used in international surrogacy are usually high quality. They are most often blastocyst-stage, frozen, and in many cases created from donor eggs from young, screened donors. The implantation potential per embryo is already strong. Adding a second embryo to a transfer in this context does not necessarily improve your chances of a live birth - it primarily increases the chance of a multiple pregnancy.

Second, it’s also important to recognize the surrogate’s position in this decision. In some programs, higher compensation for twin pregnancies can unintentionally create a perception that carrying twins is an acceptable “upgrade,” but that financial incentive should never override medical judgment. Even if a surrogate feels willing or motivated, twin gestations significantly increase the risk of complications, and willingness does not equal physiological suitability. Proper screening is therefore essential—not just general health screening, but a careful obstetric assessment of uterine history, prior pregnancy outcomes, and overall maternal risk profile—to determine whether carrying multiples is medically appropriate at all.

Third, the consequences of multiple gestation in surrogacy extend beyond medical risk. A twin pregnancy that ends in early preterm delivery can mean weeks or months in a NICU in a country that is not your own. It can mean delayed exit documentation. It can mean a surrogate who needs longer recovery and additional medical care that intended parents are typically responsible for funding. None of this is theoretical. These scenarios happen, and they are far more common with twins than with singletons.

There is also a research point that often goes unmentioned. Studies have shown that gestational carrier cycles tend to have higher implantation and live birth rates than non-surrogacy IVF cycles using the same age and embryo profile. Surrogates are pre-screened for prior healthy pregnancies, good uterine function, and overall health. Their bodies are, on paper, more likely to support implantation than a typical IVF patient's.

That means the rationale for transferring more than one embryo, "to maximise the chance of any pregnancy", is even weaker in surrogacy than in standard IVF. The chance is already strong. Adding a second embryo mostly adds risk.

And yet, historical data shows that adherence to single embryo transfer recommendations has been lower in gestational carrier cycles (around 42 percent) than in non-surrogate IVF cycles (around 60 percent). This is one of the gaps the international surrogacy community is actively working to close.

What the Major Guidelines Now Say

This is where the regulatory picture matters, because it shapes what your clinic is recommended to do, and in some countries, what they are required to do.

ASRM (American Society for Reproductive Medicine)

The 2021 ASRM/SART committee opinion on the number of embryos to transfer made the position clear: single embryo transfer should be strongly recommended in all gestational carrier cycles, given the health risks associated with multiple gestations for the carrier.

The 2022 update to the gestational carrier guidelines reinforced this with stronger, more explicit language. And the January 2026 ASRM policy statement on gestational carriers in the US reaffirmed single embryo transfer as the clinical gold standard.

The 2023 ASRM ethics opinion added another important layer: the gestational carrier is the sole decision-maker regarding her own medical care, including the number of embryos transferred. Intended parents cannot override that decision.

ESHRE (European Society of Human Reproduction and Embryology)

The 2024 ESHRE guideline on the number of embryos to transfer is, if anything, even more direct. Its main conclusion is summarised in a single sentence:

"No clinical or embryological factor per se justifies a recommendation of DET instead of eSET in IVF/ICSI."

In other words: in the European framework, there is no patient profile and no embryo profile that automatically justifies transferring more than one embryo. eSET is the default. Exceptions need to be argued, not assumed.

Even One Embryo Can Become Twins - Embryo Splitting

Did you know that even when a single embryo is transferred in IVF or surrogacy, there is still a small chance it can split and result in identical twins? 

In assisted reproduction, this phenomenon, called monozygotic twinning, occurs in roughly 0.3–0.4% of natural pregnancies, but in IVF cycles the rate is typically reported at around 0.7–2% per single embryo transfer, depending on factors such as blastocyst culture and laboratory techniques. While rare, it is clinically significant because it is unpredictable and cannot be prevented once implantation occurs.

If two embryos are transferred, the situation becomes more complex: each embryo carries its own risk of splitting, meaning there is a small chance of not just twins, but potentially higher-order multiples if one or both embryos divide. Although triplets from a single embryo are extremely rare (estimated at well under 0.1% of single embryo transfers in reported case literature), they have been documented in IVF settings. These scenarios are uncommon, but they are exactly why single embryo transfer is widely recommended in surrogacy, to minimize avoidable risk to the surrogate while maintaining excellent success rates.

Is There Ever a Case for Multiple Embryo Transfer?

I want to be honest here. The answer is sometimes yes, in specific situations.

For intended parents using their own eggs at older maternal ages (typically over 38 to 40), where embryo quality is already compromised and the number of available embryos is limited, a careful conversation about transferring two embryos may be appropriate. The trade-off is between accepting the multiple pregnancy risk and accepting a likely lower live birth rate per cycle.

For cases with multiple previous failed transfers despite high-quality embryos, some clinics do consider double transfer in subsequent cycles, although the evidence that this actually improves outcomes is weaker than is commonly assumed.

For cases where only lower-grade embryos are available, the argument for combining two is sometimes made, but again, the data is mixed.

If you find yourself being told that transferring two embryos is the default because it improves results, that is a moment to ask more questions. The international consensus does not support that as a general statement.

What to Ask Your Agency

If you are evaluating a clinic, an agency, or a specific cycle plan, these are the questions worth asking directly.

• What is your agency’s policy on single embryo transfer (SET), and do you actively require or strongly enforce it in surrogacy cases?

• How do you ensure that surrogates fully understand the medical risks of twin pregnancies before consenting to a cycle plan?

• What safeguards are in place to prevent intended parents or financial incentives from influencing the decision to transfer more than one embryo?

• What has been your agency’s rate of twin pregnancies in surrogacy arrangements over the past few years?

• How is surrogate consent specifically handled when it comes to embryo transfer decisions, and what happens if she is uncomfortable with the plan?

If any of these answers are vague, dismissive, or framed in a way that suggests the decision is mostly the intended parents' to make - that tells you something useful.

The Bottom Line

The shift from multiple embryo transfer to single embryo transfer over the past twenty years is one of the most evidence-based, well-supported changes in reproductive medicine.

It has reduced preterm birth rates. It has lowered NICU admissions. It has reduced maternal complications. It has saved the lives of babies and protected the health of surrogates.

It has also done all of this without significantly reducing the cumulative chance of a healthy live birth, when paired with consecutive cycles using vitrified embryos.

That is the trade-off in plain terms.

One transfer, one baby at a time. A longer path in some cases, especially if the first cycle does not work. But a path with materially fewer medical risks, fewer hospital interventions, fewer NICU days, and fewer scenarios where a journey that should have ended joyfully ends in complications nobody chose to take on.

In surrogacy, where the person carrying the risk is not the one who will raise the child, this trade-off is not a close call. It is the standard of care that responsible agencies now follow as a default, and that intended parents deserve to understand fully before they sign anything.

If your clinic, agency, or program is presenting this differently - that is worth a second conversation.

Ready to Talk Through Your Situation?

If you are exploring surrogacy and want clarity on how different agencies approach embryo transfer, surrogate safety standards, and overall cycle planning, I offer a free 30-minute discovery call.

This is a general consultation to understand your circumstances, answer your questions, and help you make sense of the often complex world of international surrogacy.

No scripts. No sales pressure. Just a clear, straightforward conversation to help you understand your options and what they mean in practice.

You can book your call here.

Olga Pysana is an independent international surrogacy consultant and the founder of The Surrogacy Insider. She has supported over 250 families through international surrogacy journeys across seven countries.

This article is for informational purposes only and does not constitute medical or legal advice. Always consult a qualified fertility specialist and reproductive attorney for guidance specific to your situation.