Using a targeted IVF technique could greatly reduce risky multiple births without curbing the overall chances of pregnancy, a study suggests.
IVF currently produces many twins and triplets
A study of hundreds of IVF patients at a London hospital found using a single, slightly more mature embryo in certain women dramatically cut multiple births.
And pregnancy rates actually increased, doctors wrote in the journal BJOG.
Doctors say choosing from older embryos allows them to identify those with the best chance of implanting in the womb.
At present, more than one embryo is often placed in the womb to increase the chances of at least one surviving.
But this frequently leads to twin or triplet births, which can place the lives of both mother and child at risk.
All the key bodies involved in IVF, including the HFEA, the British Fertility Society and the Royal College of Obstetricians and Gynaecologists, have thrown their weight behind efforts to bring the multiple birth rate down.
However as private IVF is expensive - and NHS treatment often limited to one cycle - many couples are prepared to take the risks involved in order to maximise their chances of conceiving in one go.
An older egg
This technique uses a blastocyst - a five-day-old fertilised egg which has already started to develop into placenta and foetus.
In the study at the Assisted Conception Unit at Guy's and St Thomas' Hospital, London, two groups of women were investigated.
The first group, which was treated between 2004 and 2005 before the technology was available, had up to three embryos implanted, two to three days after insemination.
Some 13% of these involved the transfer of just one embryo.
The pregnancy rate for this group was 27% and the multiple pregnancy rate 32%.
In a second group, younger women with good quality embryos who were seen most at risk of multiple pregnancies had the option of receiving a blastocyst instead.
Nearly 20% of the embryos transferred were blastocysts, and of these, the majority were single transfers.
The pregnancy rate for this group, which included older women who had received multiple implants, was 32% and the multiple pregnancy rate was 17%.
Effectively, the study suggests, by changing the treatment of a relatively small number of women, the overall multiple birth rate could be reduced by as much as 50%.
"It is a myth that single embryo transfer lowers the success rate of pregnancy," said Dr Yakoub Khalaf, who led the study.
"If the right patients are selected for blastocyst transfer, success rates can be maintained and multiple pregnancy can be significantly reduced."
According to the HFEA, about a quarter of clinics are now regularly providing blastocyst transfer.
Dr Mark Hamilton, chairman of the British Fertility Society, welcomed the study's findings.
But he also called for couples to have access to the three cycles of IVF treatment that NICE guidelines recommend, but which so few obtain.
That way, couples would be less likely to ask for multiple embryo transfers in order to improve their chances in just one cycle.
"By reducing the number of multiple births, the money you would save on premature baby care would easily be enough to fund those extra cycles," he said.