A recent article published in JAMA Pediatrics (2018; Associations of Prenatal Ultrasound and Autism Spectrum Disorders[i]) has re-drawn attention to ultrasound as a potential factor that may cause ASD. My colleague Dr. Pierre Mourad and I want to take a moment to highlight some thoughts about this research.
The search for a cause of autism has gone down a lot of paths over the years, including a lot of wrong turns and dead ends. One current theory is that ASD results from multiple “hits.” That is, multiple risk factors work together to result in autism. Specifically, the theory is that when a genetically vulnerable fetus is exposed to an environmental stressor during a critical period of brain development, autism is the result.
Could ultrasound be a potential environmental cause?
Ultrasonography consists of pulses of high-frequency sound, which provides information about the structure of tissue and the movement of blood in the body. Ultrasonography can create increases in temperature and local stress within the tissue. The longer that the ultrasound exposure lasts or the more intense the ultrasound is, there will be higher temperature and more stress, which in principle could increase the risk of tissue harm.
The FDA regulates the safety of ultrasound machines and American College of Obstetricians and Gynecologists has guidelines that call for 1 to 2 ultrasounds in low-risk pregnancies. Despite all of these factors guiding safety, research suggests that many practitioners do not understand or evaluate the physical safety during use. Moreover, more women are being exposed to higher rates of ultrasound in the 1st trimester and throughout pregnancy than would be expected in a low-risk pregnancy. It’s important to note here that ultrasound has clear medical benefits during pregnancy so we don’t want to throw ultrasound out. However, the excessive use of ultrasound during pregnancy could be problematic, which is why the FDA warns against multiple ultrasounds in low-risk pregnancies.
Does ultrasound exposure increase the risk of a child having ASD?
In this recent JAMA paper, Rossman and colleagues examined records from ~100 mothers of children diagnosed with autism, ~100 mothers of children diagnosed with developmental delay, and ~100 mothers of children with typical development. They compared rates, timing, and length of exposure to ultrasound during their pregnancy. Mothers of children with ASD were less likely to receive a 1st-trimester ultrasound and received less exposure time during their scans in both the 1st and 2nd trimester. Thus, if anything, children who developed ASD had less exposure than their typically developing peers. Thus, while the Rossman paper has gained a lot of media attention, the take-home message is that its findings are more aligned with the field – ultrasound is NOT a single-hit, causal factor in ASD.
There is still more work to be done though! We don’t know if there are subgroups of children, for example, those with disruptive genetic variants, that may be more vulnerable to environmental exposures, such as ultrasound, during fetal development. Focusing on such specific ‘gene-by-environmental’ interactions is complicated but is likely to be closer to the real risk for ASD.
We hope you enjoyed our first Science with Sara blog series. Special thanks to authors Sara Webb, Ph.D. and Pierre Mourad, Ph.D.
[i] Rosman NP, Vassar R, Doros G, DeRosa J, Froman A, DiMauro A, Santiago S, Abbott J. Association of Prenatal Ultrasonography and Autism Spectrum Disorder. JAMA Pediatr. Published online February 12, 2018. doi:10.1001/jamapediatrics.2017.5634.