Single embryo transfer: why it is the safest choice
In the past it was common to transfer two or more embryos, on the logic that this raises the chance of pregnancy. Today we know this approach carries a serious price: multiple pregnancy.
Elective single embryo transfer (eSET) has become established as the safest strategy for the great majority of patients — without sacrificing the final chance of having a baby.
Why is a twin pregnancy not a desirable goal?
Many couples initially wish for twins, seeing it as a “double blessing”. Medically, however, a twin pregnancy is a high-risk pregnancy, both for the mother and for the babies.
The risks include a markedly higher chance of preterm birth, low birth weight, pre-eclampsia, gestational diabetes and delivery complications. Preterm birth in particular is the leading cause of neonatal problems.
Doesn’t single embryo transfer reduce my chances?
In a single fresh transfer, transferring two embryos gives a somewhat higher pregnancy rate than transferring one. But that is not the right comparison.
When we compare the strategy as a whole — that is, transferring one embryo at a time (fresh and then frozen) versus two embryos together — the cumulative live-birth rate is similar. In other words, you do not lose the chance of having a baby; you simply “spread” it safely across successive transfers.
How much is the twin risk really reduced?
Dramatically. Single embryo transfer cuts the risk of multiple pregnancy by roughly 90% compared with transferring two embryos. At the same time, it substantially increases the chance of a healthy, full-term singleton.
This safety benefit is the main reason international societies recommend single embryo transfer as the default for most patients.
Which patients are the best candidates?
Single embryo transfer is ideal when there is at least one good-quality embryo, especially at the blastocyst stage, and in younger women with a good prognosis. Culture to the blastocyst stage helps select the embryo with the highest implantation potential.
Even in some cases with a less favourable prognosis, single embryo transfer may be the more correct choice, in order to avoid a dangerous multiple pregnancy.
Are there cases where transferring two embryos is justified?
Yes, but they are selected cases and fewer than is often believed. In some older women, with repeated failures or with limited-quality embryos, transferring two embryos may be discussed, carefully weighing benefit against risk.
Even then, the decision must be individualized, informed, and take seriously the obstetric risks of a possible twin pregnancy.
What is the take-home message for couples?
The goal of modern IVF is not simply a pregnancy, but the birth of a healthy child with the greatest possible safety. Single embryo transfer serves precisely this goal.
The aim is not “as fast as possible and as many embryos as possible”, but “one healthy baby at a time, by the safest route”.
Summary
Elective single embryo transfer (eSET) is the safest choice for most patients. It cuts the risk of multiple pregnancy by roughly 90%, avoiding the serious obstetric and neonatal risks of twins. And crucially: when frozen transfers are also counted, the cumulative live-birth rate is similar to that of transferring two embryos. So you do not lose the chance of having a baby — you simply reach it by the safest route. The decision remains individualized throughout.
Sources: Cochrane / IPD meta-analysis of randomized trials, single vs double embryo transfer (McLernon et al., BMJ); ASRM/ESHRE recommendations on single embryo transfer and reduction of multiple pregnancies.
⚕ Medically reviewed by Prof. Stratis Kolibianakis · Thessaloniki Medical Association Reg. No. 16340
ARTICLE 5 · IVF
