Daily news

14 February 2007

IVF increases the risk of birth defects

Babies conceived using assisted reproductive technologies have an increased risk of birth defects, according to a huge new study of Canadian children.

Researchers analysed the health records of 61,208 deliveries in 2005 in Ontario, Canada. They found babies born through assisted reproductive technologies (ART) – which include in-vitro fertilization (IVF), ovulation induction and intra-uterine insemination – were about 60% more likely to develop birth defects as those born through natural conception.

Of the 1394 ART births in the study, abnormalities were most likely to be gastrointestinal, though there was also an elevated occurrence of bone, muscle and heart-related defects.

While the increase in relative risk was large, the absolute birth defect rate in ART babies was still relatively low at 2.62%, compared to 1.87% for naturally conceived babies. IVF had the highest rate of defects among ART methods, at 2.97%, while the defect rate was 2.66% for intra-uterine insemination and 2.19% for ovulation induction.


In perspective

Darine El-Chaar at the University of Ottawa, who led the study, says this represents little threat to parents looking to have babies using ART. “It’s important to put this in perspective – the risk of premature birth and low birth weight in ART babies is much more real.”

Nonetheless, the fact that an explanation for the increase in birth defects remains elusive makes the new findings significant. Some scientists point to the medications prospective mothers take to induce ovulation as a potential culprit while others blame an as-yet-unidentified aspect of a couple’s natural infertility.

“What is it about spending three days in a laboratory that causes these children to have birth defects?” asks Richard Paulsen at the University of Southern California, US. “It isn’t anything we understand physiologically.”

One possible answer could be the disruption of DNA imprinting, a process that controls how genes are expressed. Imprinting is crucial in the initial stages of embryonic development, Paulsen says. The difference between being in a womb environment and that of a test tube for three days could potentially account for the rise in defects, he adds.

The research was presented at the Society for Maternal-Fetal Medicine’s conference on pregnancy in San Francisco, US, on 9 February.