The regulator is discarding its decades-old system to explain the risks of prescription drugs to women who are pregnant or breast-feeding, in favor of a more-detailed explanation of potential risks and benefits.

Women currently rely on a system that uses the letters A, B, C, D and X to identify risks, with Category A describing perscription drugs considered relatively safe and Category X describing drugs that could cause fetal abnormalities.

However, the FDA acknowledges the lettered scale can be confusing. Dr. Sandra Kweder, deputy director of the Office of New Drugs in the FDA’s Center for Drug Evaluation and Research, said the system was “overly simplistic and was misinterpreted as a grading system, which gave an oversimplified view of the product risk.” Further, Dr. Joanne Stone, director of maternal and fetal medicine at The Mount Sinai Hospital in New York City, said the system fails to provide “detailed information relevant to making decisions about use in pregnancy and lactation.”

To revamp how drug products are labeled with information about how a drug may be used during pregnancy, the FDA issued a new regulation, “Content and Format of Labeling for Human Prescription Drug and Biological Products; Requirements for Pregnancy and Lactation Labeling.

While drug companies already disclose the majority of the information now required by the regulator, Dr. Kweder said the data can be confusing, out of date and “scattered.” Therefore, the aim is to organize the information in a clearer and more consistent format.

In an accompanying guidance document, “Pregnancy, Lactation, and Reproductive Potential: Labeling for Human Prescription Drug and Biological Products — Content and Format,” the FDA said the Pregnancy and Lactation Labeling Rule (PLLR) “provides a framework for clearly communicating information on the benefits and risks of using a drug during pregnancy and lactation to help facilitate prescribing decisions.”

Under the rule, the FDA is abandoning its “pregnancy categories” — A, B, C, D and X — and is instead requiring companies to include a “risk summary” of potential risks, such as structural abnormalities, embryo/fetal/infant mortality, functional impairments or growth problems potentially caused by a drug.

Labels must also include information about “scientifically acceptable pregnancy exposure registries,” which the FDA hopes will inform healthcare providers about the extent to which a product has been tested in pregnant women, and also encourage women to participate in those registries.

The rule bans the letter system for all drugs newly approved after June 2015, when it comes into effect. Labeling for existing prescription drugs approved on or after June 30, 2001, will be phased in gradually within three to five years. And in certain cases, drug companies will need to provide new information to doctors and patients.

The new system also breaks the risk into three sections: Pregnancy; Lactation; and Females and Males of Reproductive Potential.

The “pregnancy” section is a combination of the former “pregnancy” and “labor and delivery” sections, while the “lactation” section is meant to substitute the “nursing mothers” section. The FDA’s guidance said the section on reproductive potential will contain information “on pregnancy testing, contraception and infertility.” The FDA decided to include men in the pregnancy section because some drugs can cause fetal risk through men at the time of conception, or might lead to infertility.

The FDA estimates the transition into the new system will take “several years to complete, and will cost as much as $78.2 million.”