One embryo or two? Why single embryo transfer is the standard recommendation

The chance that a given embryo produces a baby depends on its own quality and on the uterus receiving it; adding a second embryo does not improve the first. In practice, transferring two embryos somewhat raises the chance that at least one implants in that cycle, but the increase is far smaller than doubling, while the chance that both implant, that is a twin pregnancy, rises a great deal. What is gained in speed is paid for in risk, and the risk falls not only on you but on the babies.

The fair comparison is not “one transfer with one embryo versus one transfer with two”, but “all my cycles with my embryos, one at a time, versus two at once”. When the remaining embryos are frozen and transferred later, the cumulative chance of a baby from the same group of embryos is similar to that of a double transfer. The difference is in time, not in the final result: the single-embryo route may take some months longer, but it avoids a twin pregnancy.

A twin pregnancy is not simply a pregnancy with two babies; it is a state of raised risk for everyone involved. About half of twins are born before 37 weeks, and some considerably earlier. Preterm birth brings low birth weight, admission to the neonatal intensive care unit, difficulty with breathing and feeding, and, in very early births, a higher risk of longer-term developmental consequences. These are not rare exceptions but common outcomes of a twin pregnancy.

For the mother, the risk of preeclampsia, gestational diabetes, anaemia and postpartum haemorrhage is clearly higher, and caesarean birth is much more frequent. Antenatal care requires more visits, more scans and usually delivery in a centre with neonatal services. When a couple says it would be lovely to finish with two children at once, we understand the wish, but our job is to explain what it means for those nine months and for the years that follow.

Data presented at ESHRE in 2026 make this calculation concrete. In an Australian cohort of about 18,000 women, roughly 68 per cent achieved a cumulative live birth within three cycles, while about 95 per cent of transfers used a single embryo. A programme that almost always transfers one embryo therefore reaches a strong cumulative result; safety does not require giving up the chance. This is the most convincing argument against the idea that single embryo transfer is a compromise.

At the same time the European report for 2023, covering about 1.15 million cycles, shows that transfers of more than one embryo keep falling year on year, while frozen embryo transfers rise. The two trends are connected: today's freezing techniques preserve embryos with minimal loss, so there is no longer a reason to use several at once. This is why the ESHRE and ASRM recommendations set single embryo transfer as standard practice for most patients.

A standard recommendation is not an absolute rule. Transferring two embryos may be discussed in older women, when embryos are of lower quality, after several cycles in which good-quality embryos did not implant, or when the number of available embryos is limited. The ASRM guidance ties the limits to age and prognosis rather than to the wish of the moment, and in every case it keeps single embryo transfer as the first option where the prognosis is good.

The decision is made together, once you have seen your own numbers: how many embryos you have, at what stage and quality, how many can be frozen, and what the cumulative chance of the single-embryo plan is. If embryos can be frozen safely, transferring one at a time is usually the better choice financially as well, because one stimulation cycle can cover several transfers. If you feel pressed by time, by family or by cost, say so openly; those are real reasons and they deserve to be built into the plan rather than set aside.