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How Many Embryos to Transfer in IVF: Single vs. Two

For most IVF patients today, a single embryo transfer (SET) is recommended over transferring two at once. Transferring two embryos significantly raises the risk of twins — which carries real health risks for both parent and babies — without proportionally improving the chance of one healthy baby. ASRM and SART guidance recommends eSET in patients with a good prognosis.

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Why did the recommendation shift toward single embryo transfer?

For many years, transferring two embryos at once was standard practice because it seemed to improve overall pregnancy rates. Over time, the data showed a more complicated picture: transferring two embryos did produce more pregnancies, but a substantial portion of those pregnancies were twins — and twin pregnancies carry meaningfully higher rates of preterm birth, low birth weight, NICU admission, and maternal complications compared to singleton pregnancies.

The American Society for Reproductive Medicine (ASRM) and the Society for Assisted Reproductive Technology (SART) have updated their guidance to recommend elective single embryo transfer (eSET) in patients with a good prognosis 1. A separate 2022 ASRM committee opinion on multiple gestation reinforces this direction, describing multiple pregnancy as an adverse outcome of infertility treatment that clinicians should actively work to prevent 2. The goal is to maximize the chance of one healthy, full-term baby per transfer — not to maximize the number of pregnancies. Frozen embryo storage means that additional embryos can be transferred in future cycles if the first does not succeed.

When is single embryo transfer most strongly recommended?

The ASRM/SART guidance identifies criteria for patients where a single embryo transfer is most appropriate 1:

  • Age under 35 with a good ovarian response and at least one high-quality embryo
  • Chromosomally tested embryo (PGT-A euploid) — when an embryo has been confirmed to have the correct number of chromosomes, transferring one provides a high per-transfer success rate with low twin risk
  • Favorable uterine environment — no significant structural abnormalities
  • No prior failed transfers with good embryos — a history of repeated implantation failure may shift the conversation, though even then, clinical guidelines do not generally support transferring more than two embryos

For patients over 38, those with diminished ovarian reserve, or those who have had multiple previous failed transfers, the conversation about number of embryos becomes more nuanced — but two is generally the maximum recommended even in less favorable circumstances 1.

What are the real risks of a twin pregnancy from IVF?

Twin pregnancies, while often seen as a desirable outcome, carry significant medical risks that are important to understand before choosing to transfer two embryos 2:

  • Preterm birth — twins are far more likely to be born before 37 weeks than singletons, and preterm birth is the leading cause of neonatal illness and death
  • Low birth weight — shared uterine environment and earlier delivery mean individual babies tend to weigh less
  • Longer NICU stays — preterm twins often require neonatal intensive care
  • Higher-order multiples — two embryos can occasionally result in three fetuses if one embryo splits (identical twins plus the other embryo)
  • Maternal complications — preeclampsia, gestational diabetes, cesarean delivery, and postpartum hemorrhage are all more common in twin pregnancies

These risks are why professional societies frame twin pregnancy from IVF as a complication to avoid, not a bonus outcome 2.

What about PGT-A and embryo selection?

Preimplantation genetic testing for aneuploidy (PGT-A) screens embryos for chromosomal abnormalities before transfer. When a euploid (chromosomally normal) embryo is confirmed, per-transfer success rates are substantially higher and the rationale for transferring a single embryo is strongest — there is little additional benefit from transferring two euploid embryos, and doing so meaningfully increases twin risk 1.

However, a 2024 ASRM committee opinion noted that PGT-A has not been demonstrated to benefit all IVF patients as routine screening. The decision about whether to pursue PGT-A should be made based on individual factors — including age, embryo history, and clinical judgment — not as a universal add-on.

What about transferring two if I want twins?

This comes up frequently, and it is worth being direct: most reproductive endocrinologists will have an honest conversation about the medical risks before agreeing to transfer two embryos in a patient with a good prognosis. The risks to both the babies and the birthing parent are real, and the medical community's shift toward single embryo transfer reflects a commitment to the health of all parties involved 2.

If this is a priority for you, discuss it openly with your clinician — including what the realistic twin probability would be in your specific situation, what the medical risks mean for your health, and whether your obstetric provider is equipped to manage a twin pregnancy.

Common questions

Does single embryo transfer lower my overall chance of having a baby?

Not meaningfully, when frozen embryos are stored. If the first single transfer does not result in pregnancy, remaining embryos can be transferred in subsequent cycles. The cumulative rate of achieving a live birth over multiple frozen transfers with stored embryos is comparable to transferring two at once — with less twin risk per cycle.

Does PGT-A testing make single embryo transfer more reliable?

Yes. When an embryo has been tested and confirmed to be chromosomally normal (euploid), the per-transfer live birth rate is higher and miscarriage rates are lower. This makes single embryo transfer a more confident choice because you are transferring one highly vetted embryo rather than hoping chance favors one of two untested ones.

What if I only have one embryo to transfer?

If you have only one embryo available, the number question resolves itself. Your clinician will focus on optimizing the uterine environment and timing to give that embryo the best possible chance.

Can I request to transfer two embryos even if my doctor recommends one?

This is ultimately a shared decision between you and your clinician. ASRM guidelines support informed patient autonomy, and clinicians are guided — but not absolutely bound — by the recommendations. Having an honest, detailed conversation about your individual risk profile and the clinical rationale is the most important step.

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Key points to discuss with your reproductive endocrinologist

  • —Any personal history of uterine abnormalities, prior preterm birth, or cervical incompetence — all affect how a twin pregnancy would be managed
  • —Significant maternal health conditions (diabetes, hypertension, heart disease) that would make a twin pregnancy higher risk

This article provides general health education and does not constitute personalized medical advice. The decision about how many embryos to transfer is individualized and should be made with your reproductive endocrinologist after a full review of your history, embryo quality, and uterine factors. Gale can help you prepare for that conversation.

References

  1. 1.Practice Committee of the American Society for Reproductive Medicine; Practice Committee of the Society for Assisted Reproductive Technology (2017). Guidance on the limits to the number of embryos to transfer: a committee opinion. Fertility and Sterility. doi:10.1016/j.fertnstert.2017.02.107 ✓ASRM/SART guidance that elective single embryo transfer is recommended in good-prognosis patients; criteria for eSET by age and embryo quality; limits on number of embryos to transfer
  2. 2.Practice Committee of the Society for Reproductive Endocrinology and Infertility; Quality Assurance Committee of SART; Practice Committee of ASRM (2022). Multiple gestation associated with infertility therapy: a committee opinion. Fertility and Sterility. doi:10.1016/j.fertnstert.2021.12.016 ✓Multiple pregnancy is framed as an adverse outcome of infertility treatment; medical risks of twin pregnancy including preterm birth, low birth weight, and maternal complications

2 sources, numbered by first appearance. General health information, not medical advice — synthetic demonstration content.