In vitro fertilization (IVF) does not cause birth defects in children conceived with the technology. Instead, the higher rate of congenital disease in children born after IVF, compared to natural conception, is probably explained by factors underlying the parents’ infertility. Those conclusions come from a study of more than 300,000 births, published in the New England Journal of Medicine.

Children conceived through assisted reproductive technologies, including IVF and intracytoplasmic sperm injection (ICSI), are more likely to have rare congenital conditions, such as cerebral palsy and heart defects, compared to children conceived through intercourse.

A widely cited 2004 New England Journal of Medicine study, for instance, found that 8.6% of children conceived by IVF and 9% of children conceived by ICSI were diagnosed with a major birth defect by age 1, compared to 4.2% of 4,000 naturally conceived infants.

But few studies have asked whether this increased risk is a result of the reproductive technologies used — which involve hormone treatments and potentially harmful manipulations of sperm and egg — or pre-existing biological factors, such as genetic mutations, that may underlie a couple’s infertility.

A 2006 study of more than 50,000 Danish births found that infertile parents who managed to conceive naturally gave birth to children with defects at a slightly higher rate than fertile parents.

The latest study, from scientists at the University of Adelaide, Australia, takes into account potentially confounding factors that might increase a couple’s chances of conceiving a child with birth defects. These included ethnic and socioeconomic differences and the age and health of the mother.

Among 308,974 births tracked in the study, 6,163 resulted from assisted conception. As previous studies have shown, assisted conceptions led to higher rates of congenital defects (8.3%) than were seen in children conceived the old-fashioned way (5.8%).

When taking into account other factors that could increase the risk of birth defects, children conceived through IVF proved no likelier to suffer defects than children conceived naturally, whereas children conceived through ICSI were still slightly more likely to be diagnosed with a congenital disease. Moreover, couples with a history of infertility who managed to conceive naturally were also likelier to give birth to children with birth defects than fertile couples.

“In my estimation, this study is somewhat reassuring,” says Bradley Van Voorhis, a reproductive endocrinology and infertility specialist at the University of Iowa in Iowa City. “It suggests that it’s not the treatment and the things we’re doing to these gametes and embryos that are causing the problem, but more the underlying population [receiving the treatments].”

ICSI may also come with no increased risk of birth defects, says Van Voorhis. The technique is used to help men with defective sperm conceive, and the Australian researchers took into account potentially confounding factors among mothers, but not fathers.

But innovations in assisted reproductive techniques mean scientists should continue to be vigilant to potential problems, says Van Voorhis. For instance, the Australian study did not look specifically at relatively new procedures in which embryos are implanted at the 100-cell blastocyst stage, a procedure that involves several more days in culture than conventional IVF. “I think there will be continued scrutiny of this technique because it is changing and it is increasing in use and a higher percentage of children are born from assisted reproductive technology procedures,” he says. “So we’ll need to continue to observe the health of those offspring.”

Image of intracytoplasmic sperm injection via Wikimedia Commons