The Food and Drug Administration rates the safety of prescription drugs for pregnant women depending on what is known about different drugs' effects on a fetus. If the rating system is not followed, and if pregnant women are prescribed dangerous drugs, complications, birth defects, or even the death of the baby could result. Unfortunately, as researchers sponsored by the Agency for Healthcare Research and Quality found out, pregnant women and their babies are put at risk more often than they should be.

What the researchers wanted to know: How many pregnant women in the United States are taking drugs that could harm them or their fetus?

What they did: The researchers looked back at data from more than 150,000 women who delivered babies between 1996 and 2000, and who had medical records for their prenatal care—including prescriptions. All of the patients were members of an HMO, and the researchers took their prescription information from records provided by the HMO, estimating their length of pregnancy using the delivery date and counting back 270 days (the average length from conception to birth for humans). They classified the drugs prescribed based on the government's risk classification system and did not include herbal supplements or nonprescription drug use in their evaluation.

What they found: Nearly half of the women in the study received drugs which have either no safety information about their use during pregnancy, or for which there is evidence that the drugs may harm the unborn child. After the first prenatal visit, more than 2 percent, about 3,000 women, received prescriptions for drugs in one of the two most dangerous categories according to the FDA: drugs that have been found to have "definite fetal risks" associated with them. (That number excludes women who received prescriptions for contraception and fertility drugs, which are in those categories but which wouldn't be taken during pregnancy.)

What it means to you: If you are pregnant or planning on being pregnant soon, it would be wise to read the FDA guidelines for drug safety during pregnancy (see link below). Many drugs that are safe for women to take normally, such as birth control pills, can severely complicate a pregnancy or harm the fetus. Talk to your doctor if you are concerned, and research the indications of any medications you are prescribed—often the drug labels themselves will contain information about whether they are dangerous for pregnant women.

Caveats: Because the researchers estimated the length of all of the pregnancies to be a full-term, and there were no doubt babies born prematurely, the researchers likely included drugs prescribed when the women were not pregnant. Similarly, some of the women who received drugs deemed dangerous for pregnancy may have been prescribed those drugs for use after pregnancy; the researchers had no way to separate those women from women who actually used the drugs during gestation.

Find out more: The National Women's Health Information Center has information about what drugs are and are not safe to take during pregnancy, and why.

The National Institutes of Health provides safety information on many prescription drugs.

Read the article: Andrade, S.E. et al. "Prescription Drug Use in Pregnancy." American Journal of Obstetrics and Gynecology. August 2004, Vol. 191, No. 2, pp. 398-407.

Abstract online: http://www.ncbi.nlm.nih.gov