Category B: Animal reproduction studies have been performed and have revealed no evidence of impaired fertility or harm to the fetus.
Animal studies have shown an adverse effect, but adequate and well-controlled studies in pregnant women have failed to demonstrate a risk to the fetus during the first trimester of pregnancy, and there is no evidence of a risk in later trimesters.
Category C: Animal reproduction studies have shown that this medication is teratogenic (or embryocidal or has other adverse effect), and there are no adequate and well-controlled studies in pregnant women.
There are no animal reproduction studies and no adequate and well-contolled studies in humans.
Category 0: This medication can cause fetal harm when administered to a pregnant woman. If this drug is used during pregnancy or if a woman becomes pregnant while taking this medication, she should be apprised of the potential hazard to the fetus.
Category X: This medication is contraindicated in women who are or may become pregnant. It may cause fetal harm.
aMedications approved after June 2015 are not assigned a letter category, whereas older medications will have letter categories phased out after this date.
implications of the underlying condition for which the drug is given. Risks associated with not treating the condition are also described. Even the manner in which information is presented afects perception. For example, women given negative information-such as a 2-percent chance of a malformed newborn-are more likely to perceive an exaggerated risk than women given positive information-such as a 98-percent chance of an unafected infant Gasper, 2001). Instead of citing a higher odds ratio, it may be helpful to provide the absolute risk for a particular defect or the attributable risk, which is the diference between prevalence in exposed and unexposed individuals (Conover, 2011). The association between oral corticosteroid medications and cleft lip sounds far more concerning when presented as a tripling or 200-percent increase in risk than when described as an increase from 1 per 1000 to 3 per 1000 or as a 99.7 -percent likelihood of no cleft development following exposure.
With a few notable exceptions, most commonly prescribed drugs and medications can be used with relative safety during pregnancy. Many drugs discussed in this chapter are lowrisk teratogens, which are medications that produce defects in fewer than 10 per 1000 maternal exposures (Shepard, 2002a). Because risks conferred by low-risk teratogens are so close to the population background rate of fetal anomalies, they may not be a major factor in deciding whether to discontinue treatment for an important condition (Shepard, 2002b). Remember that al women have an approximate 3-percent chance of having a newborn with a birth dect. Although exposure to a confirmed teratogen may elevate this risk, the magnitude of the increase is usually only 1 or 2 percent or at most, doubled or tripled. The concept of risk versus benefit is often central to counseling. Some untreated diseases pose a more serious threat to both mother and fetus than medication exposure risks.
Considering the thousands of compounds available, relatively few medications and other substances are considered to be major human teratogens. The most common examples are listed in Table 12-1. With few exceptions, in every clinical situation potentially requiring therapy with a known teratogen, alternative drugs can be given with relative safety. Realizing limitations in available evidence, pregnant women should be advised to take any medication only when it is clearly needed. In general, targeted sonography is indicated if there has been exposure to any major teratogen during the embryonic period.
Ethanol is a potent and prevalent teratogen. It is considered the leading cause of preventable developmental disabilities worldwide (Hoyme, 2016). In the United States, 8 percent of pregnant women report drinking alcohol and between 1 and 2 percent admit to binge drinking (Centers for Disease Control and Prevention, 2012).