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WOULD-BE parents might want to persevere with old-fashioned sex for a little longer before resorting to IVF. One of the most comprehensive studies to date suggests that babies conceived by IVF are more than twice as likely to suffer major birth defects as babies conceived naturally.

The controversial findings, which are the first to suggest such a high rate of malformations, come amid concern about the aggressive marketing and growing use of IVF in countries such as the US.

No one knows whether the defects are linked to the factors that make couples infertile in the first place, or to aspects of IVF, or to both. If IVF itself is responsible, then clinics that push it on couples who may not need it are creating avoidable health risks, warns Allen Mitchell of Boston University School of Public Health in an editorial accompanying the study.

But even with the increased risk, a couple who conceive after IVF or intracytoplasmic sperm injection (ICSI) still have over a 90 per cent chance of having a healthy baby, stresses epidemiologist Jennifer Kurinczuk of the University of Leicester, a member of the team that carried out the research. And many defects can be surgically corrected.

“This level of risk will be acceptable to some,” Kurinczuk says, but adds that infertility clinics should spell out these risks to their clients. “People considering IVF have to be aware of this and take it into account in their decisions.”

Together with colleagues at the University of Western Australia and other institutes in Perth, she examined records of pregnancies, deliveries and birth defects for babies conceived after infertility treatment in Western Australia between 1993 and 1997. Of the 837 IVF babies, 9 per cent had major defects, such as a hole in the heart or a cleft palate. For the 301 babies conceived by ICSI, the figure was 8.6 per cent. By contrast, only 4.2 per cent of the 4000 naturally conceived babies had major defects. Babies conceived artificially were also more likely to have more than one defect.

Other studies have not shown an increased risk. One Dutch study found birth defects in only 3 per cent of ICSI babies, for example. But Kurinczuk says the data her team used is more complete because, unusually, Western Australia requires all IVF procedures and birth defects to be registered.

Another difference is that many earlier studies used narrower definitions of birth defects, such as those “that cause functional impairment or require corrective surgery”. Kurinczuk’s team believe such definitions are too narrow. For example, being born with one kidney doesn’t cause problems in children and cannot be corrected, but could cause problems in later life.

But Robert Winston, a leading IVF researcher at Imperial College, London, warns that the study relied on the small population of Western Australia, which might not be representative. “The results should be interpreted cautiously.”