Fears regarding the risks of fertility treatment have grown after doctors warned that IVF babies faced a more troubled birth than those conceived naturally.

Fears regarding the risks of fertility treatment have grown after doctors warned that IVF babies faced a more troubled birth than those conceived naturally.

Single babies born to women following fertility treatment are twice as likely to be premature and three times more likely to be very small, with a birthweight below 1500g.

They are more likely to be born by Caesarean section, to need care in the intensive care unit and have a 68 per cent greater risk of being stillborn or dying in the first week of life (up from 8 to 12.4 deaths per 1,000 pregnancies).

Fertility treatment is already known to increase the risks of a multiple pregnancy which results in problems at birth because of the extra burden of sustaining two babies in the womb and then delivering them. But the new research is the first to show that women carrying single babies conceived with the help of fertility treatment are also at greater risk at birth.

The authors, from the Leiden University Medical Centre in the Netherlands, reviewed 25 studies which compared the outcome of pregnancies following fertility treatment and natural conception published over the past two decades.

In addition to the higher risks for single babies, they found twins conceived through fertility treatment were also more likely to be admitted to intensive care, and had higher rates of premature birth, Caesarean delivery and low birthweight.

But the differences were much less marked than between the groups of single babies, and death rates among twins conceived with fertility treatment were lower.

The authors, whose findings are published online by the British Medical Journal (www.bmj.com) today, say that 25 years after the birth of the world's first test-tube baby, challenges remain.

Up to now research has focused on successful conception but the focus should now switch to achieving a successful birth, they say.

Doctors and patients have been so keen to achieve a pregnancy that they have regarded twins or even triplets as a success. But the time may now have arrived when it is appropriate to consider any multiple pregnancy "a failure of that technology to achieve what it set out to achieve".

Women having fertility treatment should be made more aware of the risks to the babies at birth and more work should be done on reducing the risks, they say.

However, they are unable to explain why the risks of birth should be higher for those babies born following fertility treatment.

"Whatever the explanation may be, singletons from assisted conception are significantly disadvantaged compared with other singletons, but this is substantially less so for twins. Women undergoing assisted reproduction should be informed of the increased risks in singleton pregnancies."

More than 68,000 babies have been born in Britain as a result of IVF. The total born following all types of fertility treatment is not known but is well above that figure.

Concern about the potential risks of treatment has grown in recent years, focused on IVF. The single biggest risk was from multiple pregnancies, which the Human Fertilisation and Embryology Authority has acted to curb by limiting the maximum number of embryos that may be transferred into the womb to two in women under 40.

Other areas of concern include the growing use of frozen embryos and eggs and the practice of injecting a single sperm directly into an egg, known as ICSI (Intra Cytoplasmic Sperm Injection).

Although there are no specific reasons to believe that children who are born as a result of fertility treatment suffer worse health, many specialists feel that the field has been allowed to develop unchecked while its long-term effects remain unknown.