Fertility treatment raises the risk of birth defects in babies, the largest study of its kind has found.
A report by the University of Adelaide published in the New England Journal of Medicine shows that on average defects were present in 8.3% of pregnancies that involved fertility treatment compared to 5.8% of pregnancies caused by natural conception.
Researchers linked a census of more than 6,100 births that occurred as a result of fertility treatment in South Australia to a registry of more than 300,000 births and 18,000 birth defects.
According to the study, in vitro fertilisation (IVF) posed the least risk to women opting for assisted conception, with defects occurring in 7.2% of pregnancies.
IVF mothers' chances of giving birth to children with defects were already higher due to factors related to their infertility problems.
IVF's main alternative, Intracytoplasmic sperm injection (ICSI), which involves the injection of a single sperm directly into an egg, posed a higher risk for defects that cannot be controlled for by female fertility factors, and resulted in defects in one in 10 pregnancies.
However, ICSI is primarily used for male fertility problems, and its risk was significantly decreased using frozen eggs, according to the study's lead author, Associate Professor Michael Davies of the University of Adelaide.
He explained: "This may be due to developmentally compromised embryos failing to survive the freeze/thaw process," adding, "while assisted reproductive technologies are associated with an increased risk of major birth defects overall, we found significant differences in risk between available treatments".
In 2005, the last year for which data was available, 5,935 babies were born as a result of IVF treatment compared to 5,265 babies born with the help of ICSI.
One surprising find within the research was a tripling of risk among women who used the drug clomiphene citrate to stimulate ovary production, though this was among a small group within the study.