Single vs Double Embryo Transfer: What Current Evidence Recommends

Written by Mannat Fertility Editorial Team | Medically reviewed by Dr. Archana Agarwal, MBBS, DipGO, Medical Director, Mannat Fertility Clinic 

How many embryos to transfer is a question sitting right at the intersection of success rates and patient safety, and the answer the evidence has arrived at is a good deal more consistent than most patients expect it to be. It is a conversation we have at Mannat Fertility with nearly every patient before a first transfer, and the reason we have it is that the evidence has shifted meaningfully across the last decade.

What Are the Two Options and How Do They Differ?

An embryo transfer in IVF places one or more embryos into the uterine cavity, in the hope that at least one of them implants. The two approaches are these:

• Single embryo transfer, or SET, where one embryo goes in per cycle
• Double embryo transfer, DET, where two are transferred within the same cycle

Through much of the early history of IVF, transferring several embryos was simply standard practice, and it was done to compensate for implantation rates that were low on a per-embryo basis. Improvements since then in embryo culture, in cryopreservation and in genetic screening have changed that calculus considerably.

What Does the Evidence Say About Success Rates?

One insight sits underneath all of the research, and it is easy to miss. Not single transfer against double transfer inside a single cycle: that is the wrong comparison to be drawing. Cumulative outcome over time is the right one, because surplus embryos get frozen and go on to be used in later transfers.

UK HFEA registry data, analysed at scale and published in Human Reproduction, found two consecutive single embryo transfers producing live birth rates comparable to or higher than one double transfer. Multiple pregnancy rates came out substantially lower as well. Put twin rates side by side and the gap is stark. The ASRM’s patient fact sheet on elective single embryo transfer gives approximately 1–2% after eSET. After a double transfer, 25–35%.

The 2023 ESHRE guidelines on the number of embryos to transfer land in the same place. Comprehensive counselling on the risks of multiple births, delivered before treatment, is what they recommend, and they hold that single transfers bring down the occurrence of multiple pregnancy set against double ones.

What Are the Risks of Double Embryo Transfer?

The primary concern is twin pregnancy with DET, also known as Double Embryo Transfer. This carries significantly higher risk compared to singletons and includes: 

• Preterm birth, low birth weight
• Pre-eclampsia. Gestational hypertension alongside it
• A caesarean section rate approximately double that of singleton births
• More admissions to neonatal intensive care
• Twin-to-twin transfusion syndrome, which occurs in identical twins

When Does the Evidence Recommend Single Embryo Transfer?

Below are the current guidelines and cases which strongly support single embryo transfer, or SET

• When a woman is under the age of 35 and has a good prognosis: This means that at least one good-quality fo embryo is available in her body.
• Next case is a frozen embryo patient, especially the ones with chromosomally screened embryos.
• Patients who plan cumulative transfers from a single retrieval have success rates that compound favourably across sequential single transfers.

When Might Double Embryo Transfer Still Be Considered?

DET may be appropriate in specific circumstances. These are usually discussed on an individual basis:

• Patients over 40 using their own eggs. Implantation rates per embryo run lower
• Repeated implantation failure despite good-quality embryos. The unexplained uterine or embryo factors have already been investigated
• Embryo quality poor across every available option, with nothing surplus to freeze

Those decisions get made case by case rather than by default. What the direction of the evidence has done over the past decade is move consistently and clearly toward single transfer as the standard of care, and not because it is the “cautious” choice, but because it produces comparable outcomes with dramatically fewer complications in the pregnancy.

If you have questions about how many embryos to transfer in your own next cycle, our team at Mannat Fertility can take you through your embryo grading and your cumulative odds and the risk picture specific to you. Book a consultation before your next transfer.

This article is for general educational purposes and is not a substitute for personalised medical advice from your fertility specialist or gynaecologist.