Prenatal Ultrasound Tied to Autism Severity in At-Risk Kids

Megan Brooks

September 21, 2016

Early prenatal diagnostic ultrasound has been linked to variability in symptoms of autism spectrum disorder (ASD) in children with specific genetic vulnerabilities.

These results "add weight to ongoing concerns" expressed by the US Food and Drug Administration (FDA) about the nonmedical use of diagnostic ultrasound during pregnancy, the authors, led by Pierre D. Mourad, PhD, University of Washington, Seattle, note.

The study was published online September 1 in Autism Research.

Hypothesis-Generating

There is some experimental evidence, though no human data, that exposure to ultrasound early in gestation could alter brain development and behavior, the investigators report.

In a retrospective study of a national sample of children with ASD, the researchers looked for a possible relationship between the severity of ASD symptoms and ultrasound exposure during the first trimester of pregnancy in offspring with a genetic predisposition to ASD.

The sample included 1749 children with ASD for whom genetic information on the presence or absence of copy number variants (CNVs) was available. CNVs represent a specific class of genetic defect that has been associated with ASD and other neurodevelopmental disorders.

For the group as a whole, exposure to first-trimester ultrasound, in comparison with no exposure, was related to lower observed social affective symptoms but greater parent-reported restrictive and repetitive behaviors, the authors report.

For the 133 children with ASD in whom CNVs had been identified, exposure to first-trimester ultrasound was related to statistically significantly lower nonverbal IQ in comparison with no exposure. There were also trends toward more impaired adaptive behaviors, as reflected in parent report, and trends toward increased observed repetitive behaviors.

For the 111 male children with ASD in whom CNVs had been identified, exposure to first-trimester ultrasound was related to statistically significantly lower nonverbal IQ and significantly increased observed repetitive behaviors, as well as trends in reduced verbal IQ and in more parent-reported repetitive symptoms.

In a statement to Medscape Medical News, the authors emphasize that they "sought to measure associations (not determine cause) in order to develop new hypotheses amenable to future study."

They also note that a post hoc analysis did not show a correlation between ASD symptom severity, presence of CNVs, and exposure to ultrasound during either the second or third trimesters. Nonetheless, they say their findings support "FDA guidelines that seek to limit diagnostic ultrasound for obstetrical care to those cases with medical need."

No Causal Link

Commenting on the findings for Medscape Medical News, Tara Wenger, MD, PhD, clinical geneticist at Seattle Children's Hospital in Washington, noted that "past studies have shown no differences in the rate of autism spectrum disorders in groups of women receiving early ultrasounds during pregnancy. These authors propose that small populations of genetically at-risk children may still have neurologic effects after exposure to ultrasound. If true, it would imply that genetic screening of pregnant women could guide practitioners when deciding about the timing of early ultrasounds."

Dr Wenger, who received her PhD in toxicology with a dissertation focused on prenatal exposures that contribute to autism, said a "noteworthy" limitation to the study is that no information was given about why the women were receiving first-trimester ultrasounds.

"Many women receive ultrasounds for routine screening, but others receive early or multiple ultrasounds because of a complication with the pregnancy," she explained.

"In this study, the women who had higher exposure to ultrasound were also older. Pregnancies of women with advanced maternal age are monitored more closely than younger women. Independent of ultrasound, older women are at greater risk of having a child with autism. So it is possible that the association in the study could be accounted for by pregnancies that were receiving more ultrasounds because they were already at higher risk," Dr Wenger said.

"It should be noted that first-trimester ultrasounds can identify serious issues with a pregnancy, and there could be risks of declining an ultrasound if an obstetrician feels it is medically necessary, so expectant mothers should discuss any concerns with their obstetrician," Dr Wenger advised.

In response to the study, the American Institute of Ultrasound in Medicine Bioeffects Committee issued a statement noting that "the results of the study do not demonstrate a causal link between ultrasound and autism. Ultrasound examinations can be safely performed by educated and credentialed sonographers and clinicians when medically indicated and when the ALARA (as low as reasonable achievable) principle is followed."

The study was supported by the National Institutes of Health and the Simons Simplex Collection. The authors have disclosed no relevant financial relationships.

Autism Res. Published online September 1, 2016. Abstract

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