The contentious issue of birth defects in babies conceived with IVF is on the boil again after a major study was published this week in the New England Journal of Medicine. Researchers at the University of Adelaide, in Australia, confirmed earlier surveys that found an elevated risk of defect among IVF babies. The odds for any birth defect in pregnancies involving assisted conception are 8.3%,  compared to 5.8% for unassisted pregnancies.

However, they said that the risk seems due to “patient factors” like obesity or smoking, not to the procedure itself. “In vitro fertilization off the hook for causing birth defects” was the headline in Nature’s news blog.

However, this was only half the story. Some fertility treatments appear to be riskier.

ICSI (intracytoplasmic sperm injection), a technique which involves injecting a sperm into the egg, is one of these. The increased risk of birth defects is 57% over normal IVF, although the absolute size of the risk is relatively small. However, ICSI is very popular. In Europe, for some reason, it is used far more often than regular IVF.

Another area of concern is the tripling of risk in women using the fertility drug clomiphene citrate to stimulate ovulation outside of a closely supervised clinical setting. "While confined to a small group in our study, this is of particular concern as clomiphene citrate is now very widely available at low cost, and may easily be used contrary to manufacturers' very specific instructions to avoid use if pregnant, as it may cause foetal malformations." says the lead author of the study, Associate Professor Michael Davies.

Surprisingly, cryopreservation (freezing) of embryos is associated with a substantially reduced risk of birth defects, particularly for ICSI. "This may be due to developmentally compromised embryos failing to survive the freeze/thaw process," says Dr Davies.