Most people undergoing fertility treatment will tell you IVF is a numbers game – and the number you want is almost always high: number of viable eggs, sperm count, pregnancy hormones. But on the question is it better to transfer one or two embryos, the jury has remained out. Now, new research may have the answer.

Traditionally there have been two schools of thought about whether implanting one or two embryos at a time will achieve the higher success rate.

One side of the argument claims the more embryos implanted, the greater the chance that at least one will take. The other side claims that the added stress of dealing with two embryos may cause the body to reject both, and that it is potentially a waste of an embryo. Usually the decision as to whether one or two embryos are used depends on the clinic.

Now, according to The Guardian, new research shows that if a healthy embryo is transferred alongside one of poorer quality, the overall chance of achieving a pregnancy is actually reduced.

In fact, according to the report, implanting two embryos, of which one is in poor health, during IVF can cut the chance of becoming pregnant by more than a quarter.

The study looked at 1,500 fresh single and double embryo transfers on day five after fertilisation, implanted in women of all ages.

Researchers believe that there may be a natural inclination by the body to ‘focus’ on the weaker embryo, rather than the healthy embryo.

It is thought that in many cases, had the healthy embryo been implanted by themselves, a successful pregnancy would have resulted.

The transfers were carried out at the Nurture Fertility clinic in Nottingham, where embryos were assessed by an embryologist using a standardised IVF grading system.

Researchers believe the findings of the study demonstrate the importance of quality over quantity.