Clinical Director of London Fertility Centre Dr. Amin Gorgy speaks on IVF research

They say a huge study - the largest of its kind - looking at the results of in-vitro fertilisation (IVF) treatments in Sweden supports their theory.

The study - which compared 5,856 IVF babies with 1.5 million non-IVF babies between 1982 and 1995 - found that the first group were five times more likely to be born prematurely and have low birthweight.

The death rate was also slightly higher, although the researchers said not significantly so.

They said that commercial pressures encouraged clinics to aim for multiple births, and that this was the reason for the difference in outcomes.

Increased dangers

Multiple births have a higher chance of being born prematurely, having a low birth weight, stillbirth or death in infanthood.

However, clinics tend to transfer two or three embryos at a time in order to increase the likelihood of the woman becoming pregnant - even though this also increase the risk of twins or triplets.

IVF techniques offer hope to childless couples

Both the authors of the paper - which was published in The Lancet medical journal - and IVF specialists reviewing the study said clinics should no longer transfer more than two embryos at a time.

Dr Karl-Costa Nygren, from the Sophia clinic in Stockholm, led the researchers, who found that a multiple birth was 27 times more likely among those receiving IVF, while abnormalities occurred in 5.4% of the IVF infants.

"The study shows us that we do not have problems with the technique, but the fact that we put in several eggs does cause a problem, and the problem is multiple pregnancies," he said.

"It is the financing that drives this thing. Clinics want to show good results and patients want to complete their treatment at the lowest possible cost.

"People are often happy with the outcome, they think twins are lovely, but the hospital care is very costly. The patient pays for the treatment, but society pays for the hospital care."

Price of success

There was no reason why eggs should not be transferred one at a time, with any other embryos being frozen for later attempts.

Although the success rate would fall a little and treatment would cost more, this was a small price to pay for the benefits associated with single births, he said.

In Sweden, the number of embryos transferred in IVF is already limited to two, he said, while in the UK doctors could still implant three.

Figures for the UK showed that about 5% of IVF pregnancies in the UK resulted in triplets.

"I think it is highly questionable that this should go on. It could be stopped overnight if we wanted," Dr Nygren said.

'Epidemic'

Professor Nicholas Fisk and Geoffrey Tew, from the Imperial College School of Medicine in London, agreed and, in a commentary in The Lancet, described an "epidemic" of multiple births in developed countries.

"Although triplet rates have begun to fall in Sweden as in the UK, reflecting increasing uptake of best practice, many clinics around the world still routinely transfer three or more embryos," they said.