In the United States alone, 639 new drug applications were approved by the Food and Drug Administration (FDA) between 1993 and 1999, and of these, 232 were new molecular entities (CDER, 1999). New drugs do not come to market with clinical trial safety data specifically designed to address questions related to human pregnancy. Once a new drug is available for clinical use, the frequency with which it is prescribed and the specific medical conditions that it is used to treat influence the likelihood that women of reproductive age will use the drug. However, numerous studies have demonstrated that pregnant women are commonly using several medications over the course of gestation. For example, in a review of drug utilization studies, Bonati et al. (1990) identified 13 publications originating from sites in the United States and Europe in which pregnant women used an average of 4.7 drugs per person with the mean number ranging from 3 to 11. A 1996 survey of records of the French Health Insurance Service demonstrated that in a sample of 1000 women living in southwest France, 99% of women received a prescription for at least one drug during pregnancy with a mean of 13.6 medications prescribed per woman (Lacroix et al., 2000).
Given that a significant proportion of pregnancies occur without prior planning—in the United States estimates are as high as 56%—women may be inadvertently exposed to medications before pregnancy is recognized, and this vulnerable period may extend into the first 4 to 6 weeks or longer following conception (Forrest, 1994). Thus, unintentional fetal exposures can occur during part or all of the most critical period in embryonic development for drug-induced malformations.
In addition to medication exposures that take place prior to pregnancy recognition, many maternal conditions, both acute and chronic, may require treatment after pregnancy is verified. A variety of relatively common diseases that occur in women of reproductive age may necessitate treatment throughout the course of pregnancy. For example, the prevalence of clinical depression is estimated to be as high as 8.0%-20.0% (Kessler et al., 1993), asthma 0.4%-1.3% (Wen et al., 2001), epilepsy 0.4%-1.0% (Holmes et al., 1994; Yerby, 2000), and rheumatoid arthritis 1.0%-2.0% (Belios and Carsons 1998) among women in their reproductive years. For some of these maternal conditions a decision not to treat could lead to events, such as uncontrolled seizure activity or psychiatric episodes, which could be detrimental to the pregnancy and/or the fetus itself (Goldberg and Nissim, 1994).
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