Women undergoing routine IVF in the UK should only have one embryo implanted, fertility experts have recommended.
Twin births can have complications
They say this will drastically reduce the rate of multiple births, which are dangerous for both babies and mothers.
Current practice is to transfer two embryos into the womb during treatment, but the group said success rates would remain the same if just one was used.
Infertility campaigners welcomed the report, compiled for the Human Fertilisation and Embryology Authority.
Presently, one in four IVF pregnancies results in twins - this is more than 10 times higher than the rate of twins born from natural conception.
But the expert group said twin births carry a number of risks compared with single babies:
- twins are three times more likely to be stillborn
- they are four times more likely to die after birth
- they are six times more likely to develop cerebral palsy
- Mothers are more likely to suffer high blood pressure and face a higher risk of morbidity
They also said that, because twins are 50% more likely to be born prematurely, their treatment costs place a heavy financial burden on the NHS.
Professor Peter Braude, who led the working group, said: "Multiple birth is the single biggest risk to the health and welfare of a child born by IVF."
Present practice in the UK is to transfer two embryos in women under 40 and three embryos for women who are older than this. But the expert group said this should change.
The group recommended the HFEA should redefine their guidelines so that single embryo transfer is used for the women most likely to become pregnant from IVF (based on age, embryo quality and the number of treatment cycles they have undergone).
They also recommend clinics should have an upper limit for the number of twins that result from their treatment, bringing proportions down to 5-10%.
Professor Braude said reducing the number of embryos transferred in one cycle would not reduce the overall success rate in IVF.
He pointed to other countries, such as Sweden, who have taken up single embryo transfer, and said studies showed the pregnancy rates had remained the same.
Professor Bill Ledger, a fertility expert from Sheffield University and another member of the committee, said: "The NHS could save a conservative £15m in the next financial year by moving to single embryo transfer."
He said that if this money could be used to pay for more treatments, this could mean an extra 7,500 cycles of treatment a year.
Professor Braude added: "We believe that we cannot as a country sit back as a country and do nothing about this."
Jane Denton, director of the Multiple Births Foundation, said: "The aim of all infertility treatment should be to have one live, healthy baby.
"The anguish of watching one or more of your children die or living with a severe disability is a situation no parent would wish to face, yet it is a frequent consequence of multiple births that is so often underestimated."
But Dr Mohamed Taranissi, medical director of the Assisted Reproduction And Gynaecology Centre (ARGC), London, said: "If the HFEA moved towards adopting single embryo transfer indiscriminately - it would probably result in a small decrease in twins but a larger number of people who do not become pregnant."
Clare Brown, chief executive of Infertility Network UK said: "We share medical concerns regarding the risks of multiple births, both to the mother and children born.
"We would support a move towards single embryo transfer, but would stress the need to ensure that the National Institute for health and Clinical Excellence fertility guideline is implemented in full, so that couples would be able to receive up to 3 full cycles of IVF on the NHS."
The HFEA said it would be considering the recommendations over the coming months before coming to a final decision next year.