The Food and Drug Administration announced a plan to strengthen drug labels to give patients and health-care professionals more precise information about how drugs affect women during pregnancy and breast-feeding.

The FDA said companies haven't done a good job of keeping up-to-date information on a label about the risks and benefits that a drug presents to pregnant women. The agency said this proposed rule, which is subject to a 90-day public-comment period, will raise awareness of the need for companies to keep the drug's label current.

The proposed label changes will likely result in the FDA taking a harder look at how drugs up for approval affect pregnant women and fetuses, said Sandra Kweder, deputy director of the FDA's office of new drugs, during a conference call.

Pregnancy labeling first appeared in 1979 and has remain unchanged since then, categorizing a drug's effect on pregnant women by letters -- A, B, C, D and X, all indicating differing levels of risk. An A label means that the possibility of fetal harm appears remote, and an X means that the risks are high.

The agency said consumers and health-care professionals have expressed concerns the categories are overly simplistic, confusing and inaccurate.

Under the proposed rule, there won't be any letter categories and information will be broken into three sections: Fetal Risk Summary, Clinical Considerations and Data.

The first section would detail what is known about the risk of the drug on the fetus and whether that information is based on animal or human studies. Clinical Considerations would explain the effects of the use of the drug if it is taken before a woman knows she is pregnant, and the final section would detail available data about the drug in human and animal studies.

Pregnancy labeling is a delicate issue because the drug can have different effects on the mother than the infant.

The FDA acknowledged in recent years it hasn't had enough information about how a drug affects pregnant women, despite evidence the data are available.