For many couples who seek infertility treatment, twins or triplets can seem the perfect outcome. A family that once seemed destined never to be becomes complete at a stroke. If a first in-vitro fertilisation (IVF) procedure is successful, there is no need for another gruelling round of therapy to provide baby with a sibling. A woman’s biological clock will not tick further towards the menopause while she waits. Many couples thus press their doctors to transfer as many embryos as they are allowed into the prospective mother’s womb. In Britain, this usually means two.

But while it is easy to see the attractions of multiple births, they are entirely illusory. Twin and triplet pregnancies are the greatest hazard of infertility treatment.

The health both of mothers and their infants is placed in significantly greater danger. Women expecting more than one baby are much more likely to develop pre-eclampsia, a potentially fatal pregnancy complication. More than half of all twins and 90 per cent of triplets are born prematurely.

Stillbirth, infant mortality and low birth weight are all more common. So, too, are serious abnormalities — triplets are ten times more likely than singletons to have cerebral palsy.

The costs are not limited to maternal and infant health. At the European Society of Human Reproduction and Embryology conference in Copenhagen this week, Professor Bill Ledger, of the University of Sheffield, presented evidence that the financial bill is also high. While each singleton baby born by IVF costs the NHS £3,313 in the first year of life, each set of twins costs £9,122. A set of triplets costs £32,354, ten times as much as a solitary infant. Jacques de Mouzon, of the Hôpital de Bicêtre in Paris, has produced similar figures for France. Caesarean sections, intensive care and the costs of lasting disabilities all play a part. Multiple births are to be avoided both in best medical and financial practice.

There is now a relatively simple way of doing this. By implanting just one embryo, the risk of twins or triplets drops almost as low as with natural conception. Doctors have traditionally been loath to do this because it has reduced the pregnancy rate — but that is starting to change.

When at least two cycles of IVF are offered to women under 40, the take-home baby rate is not much different whether one or two embryos are transferred first time round. Spare embryos can be frozen after the first attempt, so that a woman does not have to endure another round of fertility drugs if she needs another go — a frozen embryo is just thawed and implanted. If the Copenhagen conference had an abiding theme, it was that this is the way ahead for IVF. It is a course that Britain could and should take.

Ministers should insist that if the NHS is going to pay for IVF — as it has pledged to since April — normally one, and only one, embryo should be transferred. This is how the system now works in Belgium and the results have been striking: the proportion of multiple pregnancies after IVF fell from 34 per cent in 1998 to 13 per cent in 2003.

If this is to happen, however, government policy must change. For single embryo transfer to give infertile couples a fair chance of success, two or more cycles must be offered — Belgians can have six for free, and Danes five. Britain pays for just one.

The price of more would not be as steep as it seems. Though an extra £100 million or so would have to be found to provide three free cycles of single-embryo IVF, much of this could be raised through the savings on pregnancy and neo-natal care that would follow if twin and triplet births became a rarity. The measure would not quite be self- financing, but the benefits to maternal and infant health more than justify making up the difference.

Single embryo transfer is one of the most cost-effective health measures in the book. Financial excuses for dodging it will not wash.

Mark Henderson is the Times science correspondent

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