Clinics are currently permitted to return two or even three embryos to a woman's womb during IVF treatment, maximising the chances of at least one of the embryos resulting in a successful pregnancy.
But proposals from the Human Fertilisation and Embryology Authority aim to limit women to one embryo wherever possible.
The regulator says this will cut the number of multiple births and reduce the health complications associated with them.
One in four IVF babies is a twin or triplet. They are more likely to die before or during birth or to be premature, underweight or disabled. It is estimated that if all IVF children were single births, 126 fewer babies would die each year.
Multiple pregnancies are also more dangerous for mothers, who are at increased risk of miscarriage and complications.
Critics claim, however, that limiting the number of embryos would reduce the chances of a successful pregnancy and make fertility treatment even more costly for desperate couples.
Health Service funding usually covers just one cycle of treatment, explaining why three out of four couples pay thousands to go private – and have more embryos implanted.
Keith Reed, chief executive of Tamba, the Twins and Multiple Births Association, said publicly-funded treatment must be made more widely available. "It would be unfair of the HFEA to proceed with their proposals in the current climate," he said. "Instead of enacting new guidance which will potentially reduce patients' chances of conceiving, they must first work with the Government to ensure publicly-funded treatment is more widely available.
The fertilisation authority says there is a consensus among doctors, clinics and patient groups that multiple births have to be curbed on safety grounds. It has been consulting since April on a range of options including a target 10% maximum twin rate from IVF treatment which would be phased in over several years.
If a clinic hit the 10% twin target half way through the year, some couples might have to settle for one embryo or even "shop around" for a double transfer elsewhere.
The success rate for IVF is 21.6% and there are fears this figure could fall under the new policy.
