By Carolyn Crist

(Reuters Health) – Women who don’t realize they’re pregnant when they undergo magnetic resonance imaging (MRI) may be exposed to a chemical that might not be safe for the fetus, a new report warns.

The chemical, a dye called gadolinium contrast media, is used in about 30% to 45% of MRI scans in the U.S. to help enhance differences in internal organs, soft tissues, blood vessels, and bones.

“It is known that gadolinium contrast crosses the placenta and enters fetal circulation,” said lead study author Steven Bird of the Food and Drug Administration’s Center for Drug Evaluation and Research in Silver Spring, Maryland.

The safety of gadolinium-based contrast agents, or GBCAs, in pregnant women “has not been established, and their use during pregnancy is not recommended unless essential to the health of the woman or fetus,” Bird told Reuters Health by email. “Available data from cohort studies and case reports have revealed inconsistent findings regarding the association between GBCAs and adverse fetal outcomes.”

Bird and colleagues used the FDA-funded Sentinel Distributed Database to analyze data from nearly 4.7 million pregnancies in that resulted in live births between 2006 and 2017. They looked for the prevalence of MRI procedures with and without GBCAs among pregnant women, including the trimester and the location of the scan on the body.

The research team found 6,879 exposures to GBCAs in 5,457 pregnancies, representing one GBCA exam per 860 pregnancies, or about 0.1% of all pregnancies. Half of the MRIs were scans of the head, but 22% were for the pelvic and abdominal regions, which may be more likely to affect the fetus.

About 70 percent of exposures in pregnant women occurred during the first trimester, the study authors wrote in the journal Radiology.

The finding that most pregnancies with in-utero exposure to gadolinium occurred in the first few weeks, “when a woman may not yet be aware of her pregnancy . . . raises the importance for patients and healthcare providers to evaluate the possibility of pregnancy before administration of GBCA,” Bird said.

“Increased attention to pregnancy screening measures may help reduce inadvertent exposure to gadolinium,” Bird said. “Healthcare providers should use GBCAs only when the additional diagnostic information provided by contrast is necessary.”

Bird and colleagues are collaborating on and funding a follow-up study among pregnant women to evaluate fetal and neonatal outcomes after GBCA exposure during pregnancy. The FDA will also continue to monitor reports of adverse events, he said.

The American College of Radiology recommends screening women of reproductive age for pregnancy before any MRI scan and states that GBCAs should only be used after careful consideration that the benefits to the mother and fetus outweigh the potential risks.

“Gadolinium-based contrast agents are increasingly being used in magnetic resonance imaging,” said Javier Lafuente of Gregorio Maranon Hospital in Madrid, Spain. Lafuente, who wasn’t involved with this study, has researched GBCAs in MRIs.

“In general terms, these compounds are safe,” he said. Nevertheless, he added, even in patients who are not pregnant, “adverse reactions, the possibility of nephrotoxicity from these compounds, and the possibility of developing nephrogenic systemic fibrosis could have contraindications for their clinical use.”

SOURCE: Radiology, online August 20, 2019.