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Prospective MRI Study Reveals Impact of Opioid Exposure on the Fetal Brain


Researchers found that in utero opioid exposure resulted in seven out of 14 2D biometric measurements of the fetal brain being smaller on magnetic resonance imaging (MRI) scans in comparison to fetuses without opioid exposure.

In-utero opioid exposure may lead to smaller fetal brain size and increased risk for breech presentations, according to a new prospective, multicenter, magnetic resonance imaging (MRI) study.

For the recently published case-control study in the American Journal of Roentgenology, researchers assessed single fetal MRI exams obtained during the third trimester for 65 women with a mean age of 29. Twenty-eight of the fetuses had opioid exposure, according to the study. Reported opioid use included fentanyl, heroin, morphine, hydrocodone and oxycontin.1

After performing 14 two-dimensional biometric fetal brain measurements, the study authors found that seven of the measurements were smaller in fetuses with opioid exposure in comparison to those without opioid exposure. The statistically significant differences included the brain biparietal diameter (72.9 mm vs. 74.1 mm); the anterior-posterior pons (11.6 mm vs. 12.1 mm); the cerebral fronto-occipital diameter (93.8 mm vs. 95.0 mm); and the bone biparietal diameter (79.0 mm vs. 80.3 mm).1

“Despite the current widespread availability, overall ease of performance, and safety profile of fetal MRI, studies of the brain on fetal MRI in opioid-exposed fetuses are scarce,” wrote lead author Usha D. Nagaraj, MD, a pediatric neuroradiologist affiliated with the Cincinnati Children’s Hospital Medical Center, and colleagues. “To our knowledge, the present study represents one of the largest such studies to date and adds to the prior literature by illustrating that impaired head growth begins in utero.”

The study authors also found a 21 percent higher incidence of increased amniotic fluid volume (29 percent vs. 8 percent) and an 18 percent higher frequency of breech position (21 percent vs. 3 percent) with opioid-exposed fetuses in comparison to those without opioid exposure.1

“Opioid exposure during pregnancy may cause a disruption in fetal neuromuscular development, potentially at the microstructural level, that results in breech presentation,” suggested Nagaraj and colleagues.

Acknowledging the small sample size of the study, the authors noted that future studies with larger sample sizes are necessary to corroborate the study findings. Noting that 71 percent of the opioid-exposed fetuses were also exposed to nicotine, the study authors conceded the possible effect of this exposure on the study findings as previous research has demonstrated a link between prenatal nicotine exposure and smaller brain size.1,2 With the data coming from single MRI scans obtained during the third trimester, the researchers said they could not assess the potential impact of opioid exposure on longitudinal brain development or during earlier time periods of pregnancy.


1. Nagaraj UD, Kline-Faith BM, Zhang B, et al. MRI findings in third-trimester opioid-exposed fetuses with focus on brain measurements: a prospective multicenter case-control study. AJR Am J Roentgenol. 2022 Sep 28. Doi: 10.2214/AJR.22.28357. Online ahead of print.

2. Radhakrishnan R, Vishnubhotla RV, Guckien Z, et al. Thalamocortical functional connectivity in infants with prenatal opioid exposure correlates with severity of neonatal opioid withdrawal syndrome. Neuroradiology. 2022;64(8):1649-1659.

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