Contrary to some earlier findings, a large Canadian study links an increase in birth defects with babies born through fertility treatments. According to the results of the study, which was presented at a Society for Maternal-Fetal Medicine meeting in San Francisco, the overall risk appears minimal - less than three per cent for assisted conception versus less than two per cent for natural conception - but the risks for specific birth defects were notably higher. Dr Mark Walker, one of the study's leaders, hoped that people would find the results 'reassuring' because 'the absolute risks are still low'.

The study, conducted at the University of Ottawa, is the largest of its kind in North America and it compares the outcomes of 61,208 pregnancies in Ontario during 2005. Five per cent of the total births were a result of fertility treatments.

Dr Nancy Green, medical director of the March of Dimes, said the study was an important first because it comprehensively quantified specific birth defects while taking the effects of other potential causal factors such as age, smoking, gender of the babies and birth complications into account when estimating risk rates.

The study found that the greater the complexity of the fertility treatment, the higher the risk. Assisted reproduction technologies (ART) like IVF had the highest risk and the administration of ovulation-stimulating medications had the lowest.

Babies conceived through ART were almost nine times more likely to have gastrointestinal disorders, such as abdominal wall defects or abnormally located organs. The risk of cardiovascular disorders was more than double and although there was no increased risk for spina bifida and facial defects like cleft palate, the risk of malformed limbs and other deformities was slightly elevated. The study's head researcher, Darine El-Chaar, commented, 'We think this should become part of counselling couples that are infertile, especially that the degree of manipulating the egg and sperm may affect the risk of defects.'

It is already known that pregnancies achieved through ART face a higher risk of premature births and complications such as high blood pressure, diabetes and placental problems. Although previous studies found that ART babies are not at any more risk of major health problems than naturally conceived children, some studies have linked IVF to a slightly increased risk of certain rare genetic conditions caused by faulty genetic imprinting, such as Beckwith Wiedmann syndrome.