Is Single Embryo Transfer Safer and Successful? What New 2026 IVF Research Means for Surrogacy

Modern IVF may offer intended parents a strong cumulative chance of having a baby while transferring one embryo at a time. New research presented at the 42nd Annual Meeting of the European Society of Human Reproduction and Embryology (ESHRE) reported a 68.2% optimal cumulative live birth rate across up to three treatment cycles. Single embryo transfer was used in 95.3% of transfers, while the multiple-birth rate was 2.9%.

The findings do not mean that every patient has a 68.2% chance of success from one embryo transfer. They show outcomes accumulated across as many as three IVF cycles in a specific study population. Individual outcomes depend on factors including the age of the person whose eggs were used, embryo development, medical history, clinic protocols, and other circumstances.

For surrogacy journeys, the research supports an important safety principle: transferring more embryos does not automatically provide a better overall path to parenthood, and avoiding a multiple pregnancy can help protect the surrogate and the babies.

What Is Single Embryo Transfer?

Single embryo transfer, sometimes called SET or elective single embryo transfer, is an IVF procedure in which one embryo is placed in the uterus during a transfer.

In a gestational surrogacy journey, the embryo is created using the intended parent’s or donor’s egg and the intended parent’s or donor’s sperm. The embryo is then transferred to the surrogate, who has no genetic connection to the embryo when gestational surrogacy is used.

Single embryo transfer is intended to pursue one healthy pregnancy at a time. Although one embryo can sometimes divide and result in identical twins, transferring one embryo substantially reduces the main preventable source of IVF-related multiple pregnancy: transferring two or more embryos.

What Did the 2026 IVF Study Find?

Researchers analyzed 18,396 women beginning their first IVF cycle at seven Australian fertility clinics between January 2012 and December 2021. Follow-up continued through December 2023.

The research, presented at ESHRE’s 2026 Annual Meeting, reported:

Study measure	Reported finding
Women included	18,396
Australian fertility clinics	7
Single embryo transfers	95.3% of transfers
Optimal per-protocol cumulative live birth rate	68.2%
Intention-to-treat cumulative live birth rate	58.7%
Multiple-birth rate	2.9%

The researchers compared these outcomes with earlier studies, which had reported three-cycle cumulative live birth rates of approximately 53% to 59% and multiple-pregnancy rates above 20%.

The newer findings suggest that improvements in IVF laboratory and clinical practices may allow one embryo to be transferred at a time without sacrificing the overall chance of success across treatment. These practices include extended blastocyst culture, embryo vitrification, frozen embryo transfer protocols, and freeze-all strategies when medically appropriate.

The study was reported in Focus on Reproduction and presented at the 42nd Annual Meeting of ESHRE in London in July 2026.

What Does a 68.2% Cumulative Live Birth Rate Mean?

A cumulative live birth rate measures the chance of achieving at least one live birth across a defined series of treatment cycles or embryo transfers. It is different from the success rate of one transfer.

In this study, 68.2% was the optimal per-protocol cumulative live birth rate across up to three IVF cycles among participants who proceeded according to the study’s defined treatment pathway. The intention-to-treat rate, which included all participants based on their original enrollment regardless of whether every planned treatment step was completed, was 58.7%.

Therefore, the study should not be summarized as “one embryo has a 68.2% success rate.” That would be inaccurate.

The more useful message for intended parents is that success should sometimes be considered across the full group of embryos and treatment opportunities rather than judged only by the outcome of the first transfer.

Does Transferring One Embryo Lower IVF Success?

Not necessarily when success is evaluated cumulatively.

Transferring two embryos may raise the chance of pregnancy from a particular transfer in some circumstances, but it can also substantially increase the chance of twins. Transferring embryos one at a time can allow additional embryos to remain frozen for later use while reducing multiple-pregnancy risk during each transfer.

The 2026 study found that strong cumulative outcomes occurred while single embryo transfer was used in more than 95% of transfers. This challenges the assumption that transferring more embryos is always necessary to maximize the overall likelihood of a live birth.

However, the appropriate number of embryos must be determined by the fertility physician and patient based on individual clinical circumstances. No study can replace a personalized medical assessment.

Why Has Modern IVF Improved?

The researchers attributed the results to multiple advances rather than one breakthrough.

Blastocyst culture

Embryos can be cultured in the laboratory until day five or six, when they may reach the blastocyst stage. This gives embryologists additional information about development before selecting an embryo for transfer or freezing.

Embryo vitrification

Vitrification is a rapid-freezing method used to cryopreserve embryos. Improved survival after freezing and warming has made it possible to preserve embryos for later transfers more effectively.

Frozen embryo transfer

When several embryos are available, they can be transferred one at a time in separate cycles. This allows each embryo to contribute to the cumulative chance of success without transferring them together.

Freeze-all strategies

In some circumstances, a fertility physician may recommend freezing all suitable embryos and completing a transfer in a later cycle. This decision depends on the patient’s medical needs and should not be assumed to be best for everyone.

IVF laboratory improvements

The study also examined changes involving culture media, purpose-built incubators, reduced embryo disruption, and time-lapse culture. Between the earlier and later study periods, the proportion of fertilized eggs developing into usable blastocysts increased from 48.3% to 57.6%. At the same time, single embryo transfer increased and the multiple-birth rate declined.

Why Does Single Embryo Transfer Matter in Surrogacy?

Multiple pregnancy can create additional health risks for both the person carrying the pregnancy and the babies. According to the American Society for Reproductive Medicine (ASRM), multiple gestation is associated with increased maternal, fetal, and neonatal complications. These can include preeclampsia, gestational diabetes, preterm labor and delivery, low birth weight, and other complications.

ASRM guidance states that single embryo transfer should be strongly recommended in gestational-carrier cycles because of the health risks multiple pregnancy creates for the carrier. The guidance also explains that embryo-transfer limits in these cycles should consider the age of the person whose eggs produced the embryos—either an intended parent or egg donor not simply the surrogate’s age.

This distinction is important. A surrogate may be healthy and have a history of uncomplicated pregnancies, but carrying twins can still present greater medical risks than carrying one baby.

Is Double Embryo Transfer Ever Recommended?

There are circumstances in which a fertility physician may consider transferring more than one embryo, depending on factors such as:

• The age of the person whose eggs created the embryos

• Whether the embryos were genetically tested

• Embryo stage and quality

• Previous IVF and embryo-transfer outcomes

• The number of embryos available

• Medical history and individual prognosis

• The clinic’s outcome data and professional guidance

The decision should follow a careful discussion of the potential benefits, limitations, and risks. In surrogacy, the surrogate’s informed consent and health must remain central to the decision-making process.

Intended parents should not assume that requesting two embryos will shorten the journey or guarantee twins. Two embryos may result in no pregnancy, one baby, twins, or—if an embryo divides more than two fetuses.

Does the Study Apply Directly to Every Surrogacy Journey?

No. The study offers valuable evidence, but it has important limitations when applied to surrogacy.

The participants were treated at seven fertility clinics in Australia, so results may not be identical across countries, clinics, or patient populations. The research was observational rather than a randomized clinical trial. It also excluded women using donor eggs, frozen eggs, or certain genetic-testing pathways.

Many surrogacy journeys involve donor eggs, previously frozen eggs, PGT-A, or embryos created before the surrogate is matched. The study’s age-specific results therefore should not be treated as predicted success rates for an individual ACRC journey.

Clinic-specific outcomes, embryo information, and the individual medical circumstances of the intended parents and surrogate remain essential.

What Were the IVF Success Rates by Age?

The study reported the following optimal cumulative live birth rates across up to three treatment cycles:

Age group	Optimal cumulative live birth rate
Under 35	84.5%
35–37	74.4%
38–40	57.7%
41–42	30.1%

These age groups refer to the women undergoing IVF in the study, which excluded donor-egg cycles. They should not be interpreted as rates based on a surrogate’s age or as guaranteed outcomes for intended parents.

Age is only one factor influencing IVF success. Embryo development, ovarian response, diagnosis, laboratory practices, treatment completion, and other factors can also affect outcomes.

Does This Research Mean PGT-A Is Unnecessary?

No. The study does not prove that preimplantation genetic testing for aneuploidy, or PGT-A, is unnecessary for every patient.

PGT-A was used in at least one cycle by 25% of participants, and most live births occurred without its routine use. The researchers suggested that strong outcomes may be possible without using PGT-A universally.

However, PGT-A may be considered in particular circumstances, including some cases involving older egg age or recurrent pregnancy loss. Whether testing is appropriate depends on the patient’s medical history, embryos, goals, and physician’s recommendations.

Intended parents should ask their fertility specialist what PGT-A may and may not show, whether it is recommended in their circumstances, and how the result would affect embryo-selection or transfer decisions.

What Should Intended Parents Ask Before an Embryo Transfer?

Before deciding how many embryos to transfer, intended parents can ask the fertility clinic:

1. Why are you recommending one embryo or more than one embryo?

2. What is the clinic’s live birth rate per transfer and cumulative live birth rate for patients like us?

3. How does the age of the person whose eggs created the embryos affect the recommendation?

4. What are the chances of twins or higher-order multiples?

5. What risks would a multiple pregnancy create for the surrogate and babies?

6. How many embryos are available for future frozen transfers?

7. Would PGT-A provide useful information in our circumstances?

8. How are the surrogate’s preferences and informed consent documented?

These questions can help intended parents compare the desire for faster success with the medical goal of one healthy baby at a time.

How Does ACRC Surrogacy Support the Embryo-Transfer Process?

The fertility physician—not the surrogacy agency—determines the appropriate medical protocol and number of embryos to transfer. ACRC Surrogacy helps intended parents navigate the broader journey and supports communication among the professionals involved.

Depending on the journey, this may include coordination among intended parents, the surrogate, the fertility clinic, reproductive attorneys, insurance professionals, escrow providers, and other members of the surrogacy team.

Clear communication is especially important when discussing embryo-transfer expectations, multiple-pregnancy risks, medical consent, and plans for future frozen embryos. These conversations should occur before the legal agreement is finalized and before the transfer cycle begins.

Frequently Asked Questions About Single Embryo Transfer

Is one embryo enough for IVF?

One embryo can result in a healthy pregnancy and live birth. Whether a particular embryo will implant cannot be guaranteed. The 2026 research suggests that strong cumulative outcomes can be achieved by transferring one embryo at a time across treatment opportunities.

Is single embryo transfer safer than double embryo transfer?

Single embryo transfer substantially reduces the chance of a multiple pregnancy caused by transferring more than one embryo. It does not eliminate the possibility of identical twins because one embryo can occasionally divide.

Does transferring two embryos double the chance of success?

No. Transferring two embryos does not simply double the chance of a live birth. Outcomes depend on embryo and patient factors, and transferring more than one embryo increases the chance of twins or higher-order multiples.

Can one embryo become twins?

Yes. A single embryo can occasionally divide and result in identical twins, although this is less common than twins resulting from the transfer and implantation of two separate embryos.

Why is cumulative IVF success important?

Cumulative success considers the outcome across multiple treatment cycles or embryos rather than only the first transfer. This can provide a more complete picture of the chance of achieving a live birth from an IVF treatment strategy.

Is single embryo transfer recommended for surrogacy?

ASRM guidance strongly recommends single embryo transfer in gestational-carrier cycles because multiple gestation increases health risks for the carrier. The final decision must be individualized by the fertility physician with informed consent from everyone involved.

One Healthy Baby at a Time

The 2026 ESHRE research offers encouraging evidence that modern IVF can combine improving cumulative success with a significant reduction in multiple births. Its central lesson is not that one embryo guarantees a baby. It is that advances in embryo culture, freezing, and transfer strategies may allow patients to pursue success one embryo at a time.

For surrogacy journeys, this is especially meaningful. A safe and ethical process must consider not only the desire for a successful transfer but also the health of the surrogate and the babies throughout pregnancy and delivery.

If you are considering surrogacy and want to better understand embryo creation, matching, medical screening, legal coordination, and the steps leading to transfer, ACRC Surrogacy can help you prepare for your journey.

Book a free consultation with ACRC Surrogacy to speak with our team about your path to parenthood.

Medical Disclaimer

This article is provided for general educational and informational purposes only. It is not medical advice and should not be used to select the number of embryos to transfer, interpret an individual chance of IVF success, or replace consultation with a qualified reproductive endocrinologist or other licensed healthcare professional.

IVF outcomes and embryo-transfer recommendations vary according to individual circumstances. Intended parents and surrogates should discuss the potential benefits, limitations, and risks of any proposed transfer plan with their fertility physician. Research findings, professional recommendations, and clinical practices may evolve as additional evidence becomes available.

References

• Morbeck, D., et al. “Modern IVF clinical practices achieve superior cumulative live birth rates with near-universal single embryo transfer: A multi-cycle cohort study.” Presented at the 42nd Annual Meeting of the European Society of Human Reproduction and Embryology (ESHRE), London, July 2026; abstract published in Human Reproduction.

• European Society of Human Reproduction and Embryology. “Modern IVF achieves higher success rates with single embryo transfer, major study finds.” Focus on Reproduction, July 7, 2026. Read the ESHRE report.

• American Society for Reproductive Medicine. “Guidance on the limits to the number of embryos to transfer: a committee opinion.” Fertility and Sterility, 2021. Read the ASRM guidance.

• American Society for Reproductive Medicine. “Multiple gestation associated with infertility therapy: a committee opinion.” Fertility and Sterility, 2022. Read the ASRM committee opinion.

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