Reproductive technology with a higher risk

Children conceived via assisted reproductive technologies (ART) are twice as likely to suffer from autism as children conceived without such technologies, according to a study that was conducted by researchers from Columbia University, Fordham University and the U.S. Centers for Disease Control and Prevention (CDC), and published in the American Journal of Public Health.

ART refers to any fertility treatment in which the sperm and egg are manipulated outside the body. The category includes artificial insemination, surrogacy and in vitro fertilization (IVF).

In spite of the alarming findings, most of the correlation between ART and autism could be explained by previously known risk factors, such as higher maternal age and increased rates of pregnancy complications.

Once these factors were controlled for, the rest of the risk was found to stem from multiple births (including twins); when women conceived only a single child, that child did not have an increased autism risk.

Risk due to multiple births, high-risk pregnancies

In the largest study ever conducted into the link between autism and ART, the researchers examined records from California Master Birth Files and the CDC’s National ART Surveillance System for all children born in California between 1997 and 2007 — nearly 6 million. These were then compared with autism case load records from the California Department of Developmental Services for the same time period. There were a total of 32,922 children with autism in the sample, and 48,865 children conceived via ART.

The researchers found a dramatically higher rate of autism among children conceived via ART, but nearly the entire correlation disappeared when researchers adjusted for known autism risk factors including maternal age and birth complications (which are higher with ART in part because of increased incidence of multiple births).

“There is an association between IVF and autism, but when we control for the characteristics of women who are more likely to use IVF, for example, age and social status, this association is lessened significantly,” researcher Peter Bearman said.

Even after these adjustments, however, women between the ages of 20 and 34 who conceived via ART were still significantly more likely to give birth to an autistic child. In order to see whether this increased risk could be explained by multiple births, the researchers re-analyzed the data only with women who had given birth to a single child. The correlation disappeared.

Autism risks still under investigation

“While the risk of ART with respect to autism appears to be largely modifiable by restricting the procedure to single-embryo transfer, more research is needed to understand the precise mechanisms by which ART and autism are linked,” Bearman said.

The chances of a multiple pregnancy are significantly higher with IVF, because doctors regularly implant multiple embryos in order to increase the chances of successful implantation. According to the Society for Assisted Reproductive Technology, the popularity of ART has been partially responsible for a leap in the frequency of multiple births in recent decades. Since 1980, the twin birth rate has increased by more than 75 percent, and the birth rates for triplets, quadruplets and higher-number multiples have increased even more.

Autism is a developmental disorder characterized by difficulty with social interaction, social imagination and social communication. Rates have been increasing in recent decades, such that the CDC now estimates that one in 68 children fall somewhere on the autism spectrum.

The causes are not known but are likely due to a combination of genetic predisposition and environmental triggers. Environmental factors potentially linked to autism include air pollution, heavy metal contamination, vitamin D deficiency and early antibiotics exposure or other disruptions to the gut microbiome.