Repeated or lengthy use of sedation drugs and anesthesia during pregnancy may affect the development of children’s brains, according to the U.S. Food and Drug Administration (FDA).

In a Dec. 12 safety announcement, the FDA warned that studies suggest the use of general anesthetic and sedation drugs for more than three hours may cause the loss of nerve cells in the brain. As a result, the agency is ordering manufacturers of general anesthetic and sedation drugs to add warnings to the labels. Mothers in their third trimester are especially vulnerable to these negative effects.

The FDA issued the announcement to inform health-care providers, parents, and pregnant women of the potential risks of repeated or long-term exposure to the drugs.

“We recognize that in many cases these exposures may be medically necessary and these new data regarding the potential harms must be carefully weighed against the risk of not performing a specific medical procedure,” said Dr. Janet Woodcock, director of the FDA’s Center for Drug Evaluation and Research, in a statement.

Obstetricians Balk at Inclusion of Pregnant Women

While the FDA included pregnant women during their third trimester in the warning, some medical professionals are wary of the evidence.

The American College of Obstetricians and Gynecologists (ACOG) issued a practice advisory to its members in response to the warning.

“ACOG is unaware of data on pregnant women that support the FDA’s claims,” the group said. “The FDA did not seek input from ACOG, obstetrician-gynecologists, and other obstetric providers; such input would have been valuable in the development of this published safety announcement.”

The group does agree that patients should be informed of potential risks but is concerned that the warning will interfere with the decision to undergo important medical procedures.

“However, by requiring that warnings be added to labels, particularly with the limited evidence regarding potential effects and the extremely low likelihood that the threshold of fetal exposure would be reached, these warnings may cause patients and providers to inappropriately reject the use of these medically indicated drugs,” the group wrote.

While the nonprofit group has worked closely with the FDA on matters related to physician care in women in the past, the ACOG was surprised at the inclusion of pregnant women in the announcement.

“We were caught entirely off guard, and we are concerned about the practical applicability of this warning and its potentially negative impact on women’s health, particularly pregnant women,” Dr. Chris Zahn, vice president of practice activity for ACOG, said in a phone interview with Reuters.

Warning Partially Based on Animal Studies

Part of criticism surrounding the inclusion of sedation drugs and anesthesia during pregnancy and on infants is the fact that it’s based partially on animal studies.

One study of pregnant primates exposed to certain drugs in the third trimester for extended periods of time found an increase in neuronal cell loss in the fetus. The clinical significance of that study was not known, but the FDA used the data to include pregnant women in its warning.

“This is something we have been looking at, and based on the information we have, we thought it was important to get the information to the public,” FDA spokeswoman Sarah Peddicord told Reuters.

Even though some clinical human studies conducted on young children found that exposure to anesthesia in childhood was linked with various cognitive and behavioral problems, it’s unclear whether it was related to the drugs or other factors like the underlying medical condition.

The FDA has been researching the potential risks of general anesthetic and sedation drugs on children’s brain development since the first animal study on the topic was published in 1999.

Since then, the agency has held three advisory meetings on the subject and created the SmartTots program in conjunction with the International Anesthesia Research Society to study the growing concerns related to anesthesia.

The FDA agreed that more research needs to be done.

“More research is still needed to provide additional information about the safe use of these drugs in young children and pregnant women,” the agency said.