Should I Transfer One or Two Embryos? 5 IVF Tips

Should your transfer one or two embryos after an IVF cycle? It’s probably the most popular question we’re asked.      

The instinct to transfer two, whether you’re having IVF or donor eggs (fresh or frozen), is perfectly understandable. More embryos mean a higher chance of success, don’t they? Unfortunately, that’s not always the case. Putting all your eggs (or embryos) in one basket is not, in most cases, the best approach.      

The research is compelling: transfer one at a time. There are exceptions, but that’s the general rule.

Here are five reasons why single embryo transfers are the way to go.   

1. One embryo works for most patients – you don’t double your chances with two 

A large UK study into consecutive single embryo transfers is illuminating. It looked at what happened in over 71,000 IVF blastocyst transfers. Two consecutive single embryo transfers led to a live birth rate of 47%. Double embryo transfers saw a lower live birth rate of 38%. Perhaps most importantly, the risks to mother and baby were much lower after single embryo cycles.       

Compared with single embryo transfers, the double embryo transfers covered in the study saw multiple births increase significantly.  Preterm births almost tripled. Pregnancy losses doubled.

Those are sobering stats. A twin pregnancy also increases the chance of pre-eclampsia, gestational diabetes and low birthweight. ESHRE’s  guideline on the number of embryos to transfer in IVF is remarkably clear: no single clinical or embryological factor justifies transferring two instead of one.

The practical approach is this. If you have more than one viable embryo, transferring one, freezing the rest, and transferring the rest – one at a time – is the best strategy. The logic speaks for itself: you get a higher cumulative chance of a safer pregnancy and live birth.

And a key tip. Consider freezing your leftover embryos on single straws. It may cost more to do this, but if you’re having single embryo transfers in the future, it’s not optimal to thaw two embryos on one straw, transfer one, and then refreeze the other.       

2. Transferring a weaker embryo alongside a strong one is risky     

There’s another reason why double embryo transfers are counterproductive – and not all IVF patients are aware of this. When one good-quality embryo and one poor-quality embryo are transferred together, the outcome is dicey. This is because if one fails, it may cause the other to fail too.     

A retrospective IVF study into transferring a poor-quality embryo with a good-quality one found significantly lower clinical pregnancy and live birth rates than transferring two good embryos. This applied to blastocysts, not cleavage-stage embryos. So, one good quality blastocyst fares better than two blastocysts of mixed quality.

So, transferring two good-quality blastocysts may see better initial outcomes. But the risks associated with a multiple pregnancy remain. The above study is ultimately a quality vs. quantity argument. It supports single embryo transfers, ideally of a good-quality blastocyst, as optimal.

A more recent study saw something slightly different. Again, it looked at transferring low and high-quality embryos at the same time. 1,500 fresh transfer cycles were analysed and assessed by patient age. The study found that transferring embryos of contrasting quality boosted live birth rates a little. But it came at a price: a higher risk of other pregnancy issues.

Let’s break down the findings. Overall, the live birth rate rose by 8.7%, and the multiple pregnancy rate by 10%. For women under 35, the live birth rate was 6% and multiple pregnancy rates grew by 13.5%. For women over 35, the live birth rate went up by just 2.2% and the multiple risk was 14.7%.

What should we take from this? Since most IVF patients are close to aged 35, the study shows an insignificant boost in live birth rates for that age group when transferring two mixed-quality embryos. Given the higher chance of a multiple pregnancy, the question must be: why do it?         

More pragmatic findings are in a 2026 study on embryo quality. It found that good-quality embryos led to the best outcomes. But that transferring two mixed-quality embryos, when choice was limited, was better than transferring a single poor-quality one.    

So, once again, quality beats quantity. And a poor-quality embryo is usually a hindrance, not a help.   

3. When Is it okay to transfer two embryos in IVF cycles?

Is transferring two embryos sometimes okay? Yes, in specific circumstances.    

Clinics may consider a double embryo transfer if there’s been no implantation after several single embryo transfers using good-quality embryos. Or in cases of advanced maternal age when the embryos are lower quality and/or untested.

For IVF patients in their late thirties, ASRM guidance on the number of embryos to transfer says double blastocyst transfers are an option. But it also advises that each patient must be carefully vetted and made aware of the risks. For donor-egg recipients, its advice is different: single embryo transfers are still best if the egg donor is under 38 – which she probably will be.         

Do frozen cycles allow for more flexibility in the decision to transfer one or two?  A few years ago, maybe. Less so today.

We can get some clues from freeze-all IVF cycles – when all embryos are frozen for one or more FET cycles in the future. A Cochrane review into fresh and frozen embryo transfers saw no meaningful difference in live birth rates between freeze-all cycles and traditional IVF cycles (the latter involving a fresh transfer initially). However, the OHSS risk was reduced in freeze-all cycles.

The above study didn’t focus on single or double transfers. But it did point to similar success rates between fresh and frozen cycles. So, frozen cycles are no longer the lower-prognosis option they once were. So why risk transferring two in frozen cycles?                       

The final decision of how many to transfer need careful thought. If you’re older, using your own eggs, have a poorer prognosis or have a history of unsuccessful single embryo transfers, the case for putting has more weight. But it’s a calculated risk.               

4. Single transfers make physical AND psychological sense

For some patients, a single embryo transfer isn’t a decision. It’s a medical necessity.

If you’re pregnant in your late 30s or early 40s – like many fertility patients – your uterus and placenta work harder than in your 20s. One embryo reduces that strain – and the risks of placental ageing. If you’ve had previous caesarean sections, a multiple pregnancy also raises the risk of complications due to the scar. If you have a small body size, a single embryo transfer may also be best.

Then there’s the long game. Thinking of your treatment as a two- or three-cycle plan – rather than one make-or-break moment – is sensible. Only a minority succeed on the first cycle. As cycles continue, and clinics review and tweak things, your cumulative pregnancy chance will rise.

How your body responds to treatment gives your clinic valuable information for finetuning your future cycles. And it lets you draw breath, easing (hopefully) the mental strain. Be patient. Be safe. Be kind to yourself. One embryo at a time.          

5. Don’t fall for the “clinics abroad push multiples” myth

It’s a myth that “foreign clinics” encourage double embryo transfers. This misunderstanding refuses to die. Even the UK’s fertility watchdog, the HFEA, implies it. This kind of lazy scaremongering affects patients’ confidence – and it’s not right.

Most non-UK and EU clinics don’t routinely encourage double embryo transfers. Single embryo transfer is standard practice across Europe. The evidence, and strict EU regulations, demand it. The case for single embryo transfers is set out in ESHRE’s guidelines on the number of embryos to transfer in IVF cycles.

If your clinic – in your home country or overseas – suggests transferring two embryos, ask why. And what the risk factors are in your case. Ask your clinic for its multiple birth stats. If they answer clearly and persuasively, that’s a good sign.   

The final decision on transferring one or two embryos is yours. One at a time is the gold standard for most IVF patients. The evidence for that is crystal clear. Your clinic must tell you if, and why, you’re one of the exceptions.