Study Explores Prenatal Ultrasound Depth and Childhood Developmental Diagnoses

A retrospective study of screenshots from abdominal fetal ultrasounds found no association between the number or duration of ultrasounds and future development of autism spectrum disorder (ASD). For ultrasounds done during the first and second trimesters, among several parameters considered, one – deeper ultrasound wave penetration – was statistically associated with ASD compared to children with typical development. The study results, published in JAMA Pediatrics, requires prospective affirmation and does not establish causality between ultrasounds and autism. It does highlight a need for more research on ultrasound characteristics and fetal development.

The prevalence of ASD has progressively increased over the past few decades, with estimates now at one in 68 individuals affected. Research continues to work on identifying both the genetic and environmental factors that could lead to ASD. One factor that has been scrutinized is prenatal ultrasounds. As the technology has advanced, the number of ultrasounds that women have during pregnancy has increased substantially during the past several decades, and some argue that the previously established guidelines are no longer applicable.

“To our knowledge, this is the first study of its kind to examine current ultrasonography data and quantify the data as it may relate to different developmental outcomes in children,” said N. Paul Rosman, MD, the study’s first author, who is a professor of neurology at BUSM and a pediatric neurologist at BMC. “It is critical to note that this data should not be misinterpreted because an association does not prove a cause and effect.”

Ultrasounds are a vital tool used by providers to evaluate the developing fetus at different points in pregnancy. An abdominal ultrasound uses high-frequency sound waves, which are recorded and transformed into images of the fetus, the placenta and the surrounding organs. These images are evaluated by providers to determine if normal development is taking place as well as to detect abnormalities, such as fetal brain and heart issues or problems with the placenta that could pose a risk to the mother or the fetus. The American Congress of Obstetrics and Gynecology recommend one or two ultrasounds for low-risk pregnancies; however, the number of medically-necessary ultrasounds for all pregnancies, including high-risk, are determined by providers’ assessment of each woman’s risk factors and are done in order to help prevent and/or treat any complications that only an ultrasound can detect.

There were 420 total participants (328 boys, 92 girls) involved in this study, and their mothers had received prenatal care and delivered their baby at the same hospital. Following birth, a large majority of the infants/toddlers continued to receive their follow-up pediatric care at the same hospital where they were born.  Among the participants, 107 had been diagnosed with ASD, 104 with other developmental delays, and 209 were controls with typical development. They controlled for gender in the developmentally delayed and typical development groups given that the incidence of ASD is significantly higher in boys than in girls.

The researchers examined the fetal ultrasound records from these participants and determined their ultrasound exposure by looking at screenshots captured during the ultrasound and gathering data about the following factors: number and timing of scans, duration of exposure, mean (average) strength (depth, frame rate, mechanical index, and thermal index), and time of Doppler and three- and four-dimensional imaging. Both mechanical index and thermal index were within recommended guidelines for all studies. Ultrasound depth is determined by how far the ultrasound beam is from the target. Depending on the movement/position of the fetus, at times the specific area to be studied is on the side of the uterus close to the ultrasound beam, while at other times it is on the far side of the uterus, requiring a deeper ultrasound beam to reach the area to be studied.

The group classified as participants with ASD had a statistically significant greater mean depth of ultrasound penetration compared to the developmental delay control group in the first trimester scans, and a greater mean depth of ultrasound penetration compared to the typical development control group for first and second trimester scans. There was no association found between the number or the duration of the ultrasounds and future development of ASD.

“The association we found between the depth of ultrasound and ASD does not mean that ultrasounds cause autism, rather it highlights the need for more research on how this type of exposure may impact fetal development,” added Rosman.