The U.S. Food and Drug Administration plans to strengthen drug labels in order to inform patients and health care providers about the drugs’ negative effects on pregnant women or women who are breast-feeding their infants.

The current system, relying on letter designations to describe the risks of a drug when taken during pregnancy or breast-feeding is confusing and incomplete.

“The system of letter categories has led to an inaccurate and overly simplified view of prescribing in pregnancy. Most labels are sorely out of date. This system also makes it very difficult to update labeling as new information becomes available,” Dr. Sandra Kweder, deputy director of FDA’s Office of New Drugs, Center fro Drug Evaluation and Research said during a teleconference, the Washington Post reports.

The FDA has considered the new system a top priority since 1997 when it first began work on redesigning labels of prescription drugs’ effects during pregnancy and breast-feeding.

The new labels will contain explicit information on the risks carried by the respective drug. More specifically, a category “A” drug means studies have not shown a higher risk of birth defects, while “X” means the drug must not be taken during pregnancy. There are of course other letters (B, C, D) denoting various levels of evidence for potential harm or lack of data.

Also, future drug labels would carry three summaries that include information about risks to the fetus (“Fetal Risk Summary”), information about effects associated with a drug taken before a woman is aware of her pregnancy (“Clinical Considerations”) and information available about the drug’s use in humans and animals studies (“Data”).

The labels would also contain a lactation section, which will detail what is known about the drugs’ effects on a breast-fed infant.

The new labels will be more “practical and useful to clinicians and patients who are in the real world, trying to make some very difficult decisions,” Kweder said.

According to the FDA, about six million pregnancies occur in the U.S. yearly, half of them unplanned, and pregnant women and health care providers need to be informed on drugs’ effect because women take an average of three to five prescription drugs during pregnancy. Also, there are women who have medical conditions like asthma, high blood pressure, depression, or diabetes, conditions requiring continuous treatment even during pregnancy.

Women can suffer new medical problems during pregnancy or the old ones may get worse requiring drug treatment. Another reason for which the FDA wants to change the labeling system is the fact that a woman will often need and take medications while she is breastfeeding, potentially exposing her child to effects of these medications. Also, a woman’s body may change during pregnancy which can affect the dose she needs of a particular drug.

The new way of labeling drugs, designed to raise awareness on the need for companies to keep the drugs’ label current, will be subjected to a 90-day public-comment period before being approved. If enacted, the new system of labeling would replace a 30-year-old system for classifying drugs in favor of labels that provide information that is more detailed to doctors prescribing the drugs. The federal agency expects the new labeling laws to become effective no sooner than June 30, 2010.