Study shows a small increased risk of congenital abnormalities in infants exposed to opioids in utero

Reviewed by Emily Henderson, B.Sc.Feb 7 2022

A new study in CMAJ (Canadian Medical Association Journal) https://www.cmaj.ca/lookup/doi/10.1503/cmaj.211215 shows a small increased risk of congenital abnormalities in infants exposed to opioid medications in the first trimester of pregnancy.

The study analyzed administrative health data from Ontario on almost 600 000 birth parent–infant pairs to determine the association between opioid pain medications in early pregnancy and congenital abnormalities in infants. Prescribed opioid pain medications can cross the placenta and have the potential to cause harm, and about 2%–4% of fetuses are exposed to these drugs.

Among the infants included in the study, 2% (11 903) were exposed in utero to opioid analgesics, such as codeine, oxycodone, hydromorphone, tramadol, and morphine. The study found an increased risk, albeit low, of major anomalies with exposure to tramadol and morphine, and minor anomalies with exposure to codeine, hydromorphone and oxycodone. Specific congenital anomalies observed included gastrointestinal and genital anomalies, neoplasms and tumours, and ankyloglossia.

This large study adds to earlier evidence from studies conducted in Sweden and Norway and from a recent study of pregnant US Medicaid beneficiaries that suggested a small increased risk of congenital anomalies, an important finding for a pregnant person who may be prescribed opioids for pain relief.

"Both the potential for harm or distress to the pregnant person as a consequence of foregoing treatment and the subsequent risk to the infant must be considered for effective treatment," writes Dr. Susan Brogly, an epidemiologist and associate professor at Queen's University, Kingston, Ontario, with coauthors. "These findings further quantify harms associated with prenatal exposure to opioid analgesics to inform treatment choices for pain in pregnancy."