By Michelle Roberts
BBC News health reporter in Copenhagen
IVF multiple births cause considerable financial costs to the NHS, a fertility conference has heard.
Carrying one child is better for mother and baby, experts say
Triplets cost more than £32,000 compared to about £9,000 for twins and just over £3,000 for single births, Sheffield University experts claimed.
Fertility specialists at a conference in Denmark called for laws to ensure just one embryo is implanted - the UK limit for most is two per IVF cycle.
This would be better for mother and baby, and cost effective, they said.
Last May, the UK regulator said women under 40 can only have two embryos implanted per cycle.
Women over 40 can have three implanted, the Human Fertilisation and Embryology Authority said.
Belgium is one country where doctors are only allowed to implant one embryo per cycle of IVF treatment.
Professor Bill Ledger and colleagues at Sheffield University calculated the costs associated with all babies born after IVF between 2000 and 2001 in the UK.
The bulk of the 6,309 live births were single babies, while twins made up 27% and triplets 2%.
Professor Ledger's team says this is still too many multiple births, when the related healthcare costs of the neonatal care are taken into account
Multiple pregnancies are more likely to run into complications that can require longer and more expensive treatments, they explained.
Currently, the NHS pays for only a quarter of IVF treatments.
Professor Ledger argues that if only one embryo was transferred per IVF cycle, and hence avoid higher neonatal care costs, it would free up more money for more couples to have free IVF.
He said: "The political will is there. Former Health Secretary John Reid promised last year more money for IVF.
"One thing that would reduce the cost would be to follow the lead of what the Belgians have done. It's the next logical step."
People in Belgium are entitled to up to six cycles of IVF free of charge. Only one embryo can be transferred during the first two cycles.
Dr Diane De Neubourg, from the Centre for Reproductive Medicine, Antwerp, presented work showing that single embryo transfer produces babies that are healthier than those born after multiple implantations.
She said: "It is clear that more singletons who are healthy will cost less to society. In Belgium this understanding has resulted in laboratory costs for IVF and ICSI being reimbursed under a strict embryo transfer policy to secure the prevention of multiple pregnancies."
The issues are not unique to the UK.
Epidemiologist Dr Jacques de Mouzon, who has carried out work on the costs of multiple pregnancies in France, predicts infertility treatments are the cause of 30% of all twins and 60% of all triplets born in his country.
He said: "The figures show that multiple pregnancies have a very important economic impact, which should be considered together with the medical risks.
"Research shows that for healthy women, under the age of 40, who are ovulating normally, single embryo transfer, maybe over more than one cycle, achieves a similar pregnancy rate as transferring two or more embryos in one cycle - and with far fewer risks to the mothers and babies."