Is Single Embryo Transfer Safer for IVF? What 35 Years of Latin American Data Show
- Atlas Surrogacy
- Aug 26
- 9 min read
For many IVF patients—and especially gestational carrier cycles—transferring one embryo generally offers a safer path than transferring two because it substantially reduces the likelihood of twins and other multiple pregnancies. New Latin American data suggest that sequential single embryo transfers may also provide a strong cumulative chance of delivery without the elevated multiple-pregnancy risk associated with transferring two embryos together.
Modern IVF is not simply about achieving pregnancy. The goal is to help achieve the birth of one healthy baby while protecting the health of the person carrying the pregnancy.
A 2026 presentation from the Latin American Network of Assisted Reproduction, known as REDLARA, examined more than three decades of assisted-reproduction reporting across Latin America. The findings demonstrate how blastocyst culture, embryo freezing and single embryo transfer are contributing to safer, more individualized IVF strategies throughout the region.
For intended parents considering surrogacy in Mexico or Colombia, these findings also highlight important questions to ask a fertility clinic before an embryo transfer.
What Is Single Embryo Transfer?
Single embryo transfer, or SET, is an IVF procedure in which one embryo is placed into the uterus during a treatment cycle.
When the embryo is intentionally selected for transfer while other suitable embryos are available for freezing, the procedure may be called elective single embryo transfer, or eSET.
By comparison, double embryo transfer, or DET, involves transferring two embryos during the same procedure. Although transferring two embryos may increase the chance of pregnancy or delivery from that individual transfer, it also substantially increases the possibility of twins.
Single embryo transfer does not eliminate the possibility of twins completely. A transferred embryo can occasionally divide and result in identical twins. However, the risk is much lower than when two embryos are transferred.
What Did REDLARA Analyze?
REDLARA has collected assisted-reproduction information from fertility centers across Latin America for approximately 35 years. Its 2026 presentation, “Learning From Big Data: 35 Years of the Latin American Registry of Assisted Reproduction,” summarized regional reporting from 1990 through 2023.
The registry included:
More than 1.5 million initiated assisted-reproduction cycles
342,268 reported live-born infants
61,402 live-born infants reported in Mexico
14,033 live-born infants reported in Colombia
Long-term regional trends in IVF, ICSI, egg donation and frozen embryo transfer
Increasing use of blastocyst-stage embryos, embryo cryopreservation and single embryo transfer
These figures reflect voluntarily reported data from participating fertility centers. They should not be interpreted as complete national totals or as guaranteed success rates for every clinic or patient.
The REDLARA presentation nevertheless provides valuable insight into how assisted-reproduction practices have changed across Latin America and how embryo-transfer decisions can influence both success and safety.
What Did the Latin American Data Show About Single Embryo Transfer?
The REDLARA presentation compared delivery and multiple-gestation rates for fresh, autologous blastocyst transfers reported in 2023.
Transfer strategy | Reported delivery rate | Reported multiple-gestation rate |
Elective single embryo transfer | 30.8% | 1.3% |
Elective double embryo transfer | 44.7% | 26.6% |
One single embryo transfer followed by one frozen single embryo transfer | 54.5% cumulative delivery rate | Each procedure transfers one embryo |
The comparison illustrates an important distinction between success per transfer and cumulative success across more than one transfer.
Transferring two embryos produced a higher delivery rate from that single procedure, but it was also associated with a dramatically higher multiple-gestation rate. By contrast, transferring one embryo and, if necessary, later transferring a frozen embryo produced a higher cumulative delivery rate in the REDLARA presentation while avoiding the deliberate transfer of two embryos together.
These percentages describe the populations and treatment strategies included in the presentation. They do not predict the outcome of an individual IVF or surrogacy journey.
Does Transferring Two Embryos Double the Chance of IVF Success?
No. Transferring two embryos does not simply double the chance of having a baby.
Each embryo has its own implantation potential, and the outcome depends on several factors, including:
The age of the person who provided the eggs
Embryo development and quality
Whether the embryo has undergone preimplantation genetic testing
Whether the embryo is fresh or frozen
The fertility clinic’s laboratory performance
The uterine environment
The gestational carrier’s medical and obstetric history
Previous embryo-transfer outcomes
The REDLARA data showed a higher delivery rate per procedure with double embryo transfer, but the increase came with a much greater chance of multiple gestation.
When success is evaluated cumulatively rather than from only one transfer, using two sequential single embryo transfers may provide a competitive—and sometimes higher—chance of delivery while prioritizing a singleton pregnancy.
Why Can a Twin Pregnancy Be Riskier?
Twins can bring tremendous joy to a family. The medical concern is not about the value of twins; it is about the additional health risks associated with carrying more than one fetus.
According to the American Society for Reproductive Medicine, multiple gestation increases the likelihood of complications affecting both the pregnant person and the babies. These can include:
Preeclampsia
Gestational diabetes
Preterm labor and delivery
Low and very low birth weight
Fetal growth restriction
Placental complications
Postpartum hemorrhage
Neonatal intensive care
Increased perinatal illness and mortality
ASRM reports that delivery before 37 weeks occurs much more frequently in twin pregnancies than in singleton pregnancies. Many of the neonatal complications associated with multiple gestation are connected to premature birth.
For this reason, professional guidance identifies the birth of one healthy baby at a time as the preferred outcome of assisted reproductive treatment.
Why Is Single Embryo Transfer Especially Important in Surrogacy?
In a gestational surrogacy journey, intended parents, the gestational carrier and the medical team share an interest in reducing avoidable pregnancy risks.
A multiple pregnancy may create additional physical and emotional demands for the gestational carrier and could increase the possibility of:
More frequent medical appointments
Activity restrictions or bed rest
Hospitalization during pregnancy
Preterm delivery
Cesarean delivery
A longer recovery
NICU care for the babies
Additional medical and financial uncertainty
ASRM’s embryo-transfer guidance states that single embryo transfer should be strongly recommended in all gestational carrier cycles because of the health risks associated with multiple gestation.
The guidance also explains that transfer decisions should consider the age of the person who produced the eggs—whether that is an intended parent or an egg donor—rather than the gestational carrier’s age alone.
Does REDLARA Recommend Single Embryo Transfer?
The REDLARA presentation concluded that single embryo transfer should generally be the preferred approach, particularly when a patient produces more than ten mature eggs or develops more than one blastocyst.
Having multiple blastocysts may allow the medical team to:
Select one embryo for the first transfer.
Cryopreserve other suitable embryos.
Evaluate the outcome of the first procedure.
Conduct a later frozen embryo transfer if necessary.
This approach focuses on the cumulative chance of having a baby rather than attempting to maximize the outcome of one transfer at the cost of a substantially higher twin-pregnancy risk.
How Do Embryo Quality, Age and Egg Source Affect the Decision?
Embryo-transfer recommendations are individualized. A fertility physician may evaluate several factors before recommending a single or multiple embryo transfer.
Age of the egg source
Embryo implantation potential is closely associated with the age of the person who provided the eggs at the time the embryos were created.
In an egg-donation cycle, the egg donor’s age is therefore more relevant to embryo-transfer planning than the age of the intended parent or gestational carrier.
Embryo development
A blastocyst is an embryo that has developed for approximately five or six days after fertilization. Reaching the blastocyst stage provides the embryology team with additional information about development, but it does not guarantee implantation or a healthy birth.
Embryo quality
Embryologists assess an embryo’s appearance and development using laboratory grading systems. Embryo grading can help inform selection, but it cannot predict an outcome with certainty.
Previous IVF outcomes
The physician may review prior implantation failures, pregnancy losses, live births and the quality of the remaining embryos.
Medical history
Any medical condition that could make a multiple pregnancy especially dangerous strengthens the reason to transfer only one embryo.
Does PGT-A Mean Only One Embryo Should Be Transferred?
Preimplantation genetic testing for aneuploidy, or PGT-A, screens embryo samples for certain chromosomal findings. An embryo reported as euploid has the expected number of chromosomes detected by the test.
ASRM recommends transferring one euploid embryo regardless of the age of the person who provided the eggs.
However, PGT-A does not guarantee implantation, an ongoing pregnancy or the birth of a healthy baby. Testing also has limitations, and it may not be appropriate or beneficial in every IVF cycle. Intended parents should discuss the potential advantages, limitations, costs and uncertainties with a qualified fertility physician or genetic counselor.
Can Single Embryo Transfer Still Result in Twins?
Yes, but it is uncommon.
A single transferred embryo can divide and produce identical twins. ASRM describes a background multiple-gestation risk of approximately 1%–2% after single embryo transfer.
Single embryo transfer therefore reduces the risk of twins significantly, but it cannot reduce it to zero.
What Should Intended Parents Ask an IVF Clinic in Mexico or Colombia?
Intended parents should look beyond a single advertised “success rate.” Different clinics may calculate and present results differently, making direct comparisons difficult.
Consider asking:
Do you recommend single embryo transfer in gestational carrier cycles?
How do you calculate your pregnancy, delivery and live birth rates?
What are your success rates per transfer and cumulatively across multiple transfers?
What are your twin and multiple-pregnancy rates?
Are your statistics separated by egg-source age, donor eggs and embryo type?
How do you assess embryo quality?
When do you recommend blastocyst transfer?
What are your embryo-freezing and thaw-survival rates?
When might you recommend PGT-A, and what are its limitations?
What happens if the first embryo transfer is unsuccessful?
Under what circumstances would you consider transferring more than one embryo?
How is informed consent handled with the gestational carrier?
How do you coordinate care if the gestational carrier experiences complications?
Can you explain your laboratory accreditation, quality controls and outcome reporting?
A reputable fertility professional should explain both the potential benefits and the risks of each option without promising a guaranteed outcome.
Is Single Embryo Transfer Always the Right Choice?
Single embryo transfer is strongly supported for gestational carrier cycles and for many patients with a favorable prognosis. However, medical treatment must still be individualized.
In limited circumstances, a physician may consider a different approach based on factors such as:
The age of the egg source
Embryo stage and quality
Whether embryos have been tested
Previous unsuccessful transfers
The number of embryos available
The patient’s overall prognosis
Relevant medical history
Clinic-specific outcome data
The final recommendation should come from the treating fertility physician after counseling the intended parents and gestational carrier about the potential benefits, limitations and risks.
How Atlas Surrogacy Supports Intended Parents
Atlas Surrogacy helps intended parents explore structured family-building programs in Mexico and Colombia and connect with independent fertility professionals who can evaluate their specific medical circumstances.
Atlas does not decide how many embryos should be transferred and does not provide medical services. All IVF procedures, embryo evaluations and transfer recommendations are handled by licensed fertility clinics and physicians.
Our role is to help intended parents understand the stages of the journey, communicate with relevant professionals and ask informed questions about their available options.
Frequently Asked Questions
Is single embryo transfer safer than double embryo transfer?
For many IVF and gestational carrier cycles, single embryo transfer is considered safer because it substantially reduces the risk of twins and higher-order multiple pregnancies. Individual risks and potential benefits should be reviewed with a fertility physician.
Does transferring two embryos increase the IVF success rate?
It may increase the chance of pregnancy or delivery from one transfer, but it does not double the chance of success. It also substantially increases the risk of twins. Cumulative success after sequential single embryo transfers may be comparable or higher in appropriately selected patients.
Is single embryo transfer recommended for surrogacy?
ASRM strongly recommends single embryo transfer in gestational carrier cycles because multiple pregnancy creates additional risks for the carrier and babies.
What is the success rate of single embryo transfer in Latin America?
In the 2023 fresh autologous blastocyst data presented by REDLARA, elective single embryo transfer was associated with a 30.8% delivery rate. This regional figure should not be used to predict an individual outcome because success varies by egg-source age, embryo characteristics, clinic performance and medical history.
Can a frozen embryo transfer be successful?
Yes. Advances in vitrification have made frozen embryo transfer an important part of modern IVF. Results depend on embryo quality, laboratory performance, age at egg retrieval and other clinical factors.
Is PGT-A required before single embryo transfer?
No. PGT-A is not required for single embryo transfer and is not appropriate for every patient. Its possible benefits and limitations should be discussed with a fertility physician.
Does Atlas Surrogacy provide IVF treatment?
No. Atlas Surrogacy is a coordination and consulting organization. Medical procedures are performed by independent licensed fertility clinics and physicians.
Begin Your Surrogacy Journey With Informed Guidance
Choosing a fertility clinic and understanding embryo-transfer options can feel overwhelming, particularly when your journey involves another country.
Atlas Surrogacy helps intended parents explore family-building options in Mexico and Colombia and connect with independent medical and legal professionals who can provide individualized guidance.
Medical Disclaimer
This article is provided for general educational purposes only. It is not medical advice and should not be used to diagnose a condition, select an IVF protocol or determine how many embryos should be transferred. IVF outcomes vary significantly based on individual medical circumstances, embryo characteristics, laboratory performance and other factors. All medical decisions must be made with a qualified fertility physician. Atlas Surrogacy does not provide medical, legal or psychological services and does not guarantee treatment, pregnancy or birth outcomes.
References
Latin American Network of Assisted Reproduction. Learning From Big Data: 35 Years of the Latin American Registry of Assisted Reproduction. Presented in 2026; registry outcomes through 2023.
American Society for Reproductive Medicine. Guidance on the Limits to the Number of Embryos to Transfer: A Committee Opinion.
American Society for Reproductive Medicine. Multiple Gestation Associated With Infertility Therapy: A Committee Opinion.
Comments