Prenatal Ultrasound and Autism: Is There a Connection?

BACKGROUND AND PURPOSE:

• Approximately 1/68 children are thought to be affected with autism spectrum disorder (ASD)
• Claims have been made that increasing use of prenatal ultrasound may be related to increasing rates of autism
• Rosman et al. (JAMA Pediatrics, 2018) studied whether there is an association between prenatal ultrasound exposure and the development of ASD

METHODS:

• Case-control study
• Population: Patients with ASD and control groups with developmental delay (without ASD) or typical development were identified retrospectively
• Ultrasonographic exposure was quantified by
  • Number and timing of scans
  • Duration of exposure
  • Mean strength (depth, frame rate, mechanical index, and thermal index)
  • Time of Doppler
  • 3- and 4-dimensional imaging
• Main outcomes
  • Ultrasound exposure and associated ASD risk were compared among the above groups, adjusting for infant sex, gestational age and maternal age
  • Ultrasound exposure was quantified and compared per trimester and entire pregnancy

RESULTS:

• Data were collected from 420 participants
  • 328 boys (78.1%); 92 girls (21.9%)
  • Mean age of follow up: 6.6 years
• ASD group
  • Received their first scan a mean of 10 days later than those with typical development
  • Were more likely to have received late prenatal care, and born to mothers ≥35 years of age
    • Socioeconomic factors may play a role, associated with increased risk for ASD and less access to prenatal care
  • Comparing ASD to developmental (non-ASD) delay group, there was no statistical difference in the timing of the initial scan, the number of scans or total exposure time
  • There was no statistical difference in the timing or duration of Doppler, 3-D, or 4-D studies in ASD group compared to the other 2 groups
  • The number of scans was not significantly different between groups
    • 5.9 scans in the ASD group (95% CI, 5.2-6.6),
    • 6.1 scans in the developmental delay group (95% CI, 5.4-6.8)
    • 6.3 scans in the typical development group (95% CI, 5.8-6.8)
  • Compared with the typical development group, the ASD group had shorter duration of ultrasound exposure during first and second trimester
    • First trimester: 290.4 seconds (95% CI 212.8-368.0 seconds) in the ASD group vs 406.4 seconds (95% CI, 349.5-463.3 seconds) in the typical development group
    • Second trimester: 1687.6 seconds (95% CI, 1493.8-1881.4 seconds) in the ASD group vs 2011.0 seconds (95% CI, 1868.9-2153.1 seconds) in the typical development group
  • ASD group had a greater mean depth of penetration compared to developmental delay group
    • First trimester: 12.5 cm (95% CI, 12.0-13.0 cm) in the ASD group vs 11.6 cm [95% CI, 11.1-12.1 cm) in the developmental delay group
  • ASD group had a greater mean depth of penetration compared to typical development group
    • First trimester: 12.5 cm (95% CI, 12.0-13.0 cm) in the ASD group vs 11.6 cm (95% CI, 11.3-12.0 cm) in the typical development group
    • Second trimester: 12.9 cm (95% CI, 12.6-13.3 cm) in the ASD group vs 12.5 cm (95% CI, 12.2-12.7 cm) in the typical development group

CONCLUSION:

• Mean number of scans was >5, higher than that typically recommended for normal pregnancies
• ASD group did not have increased number of scans, and had shorter duration of ultrasound exposure when compared to typical development group
• There was a significantly greater mean depth of ultrasonographic penetration in the ASD group compared with the developmental delay group in the first trimester and compared with the typical developmental group in the first and second trimester
• Study limitations noted by authors include
  • Retrospective
  • Study did not include preterm infants who are at higher risk for ASD
  • Accurate data on smoking, which is associated with ASD, was not available
  • Association between BMI, gestational diabetes and ultrasound depth requires further evaluation
• The companion editorial included the following discussion points
  • The increased depth of ultrasound may actually indicate less exposure “because ultrasonography attenuates as it propagates, and a larger propagation distance for children with ASD would mean less exposure in utero (all else being equal)”
  • Overall findings in this study do not support the concept that ultrasound is a single causal factor in ASD

Learn More – Primary Sources:

Association of Prenatal Ultrasonography and Autism Spectrum Disorder

Editorial: Prenatal Ultrasonography and the Incidence of Autism Spectrum Disorder