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All infectious diseases have a tendency to bring about death of the child and its subsequent expulsion from the uterus. The fatal result is usually due to the transmission of toxins, and occasionally the specific micro-organisms from the mother to the child. Poisoning with phosphorus, lead, illuminating gas, and other substances may lead to similar results.

—J. Whitridge Williams (1903)

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INTRODUCTION

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Other than referring to fetal deformities that might impede vaginal delivery, little is written in the first edition of this book regarding teratogens and fetal malformations. This is despite the fact that birth defects are common, and 2 to 3 percent of all newborns have a major congenital abnormality detectable at birth (Cragan, 2009; Dolk, 2010). There are undoubtedly medications that pose significant risk to the developing embryo or fetus (Table 12-1). However, 80 percent of birth defects do not have an obvious etiology, and of those with an identified cause, nearly 95 percent of cases have chromosomal or genetic origins (Feldkamp, 2017). The Food and Drug Administration (FDA) (2005) estimates that less than 1 percent of all birth defects are caused by medications. Their remarkably small contribution to congenital abnormalities is shown in Figure 12-1.

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TABLE 12-1Selected Teratogens and Fetotoxic Agents
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FIGURE 12-1

Etiology of birth defects. Known and unknown causes of 5504 birth defects from a population-based review of 270,878 births.

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That said, significant concern surrounds medication use in pregnancy. This is because so many pregnant women are prescribed medications and because safety data are often lacking. Investigators from the National Birth Defects Prevention Study found that women take an average of two to three medications per pregnancy and that 70 percent use medication in the first trimester (Mitchell, 2011). And, in one review of medications approved by the FDA between 2000 and 2010, the Teratogen Information System (TERIS) advisory board deemed the pregnancy risk “undetermined” for more than 95 percent of these agents (Adam, 2011).

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TERATOLOGY

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The study of birth defects and their etiology is termed teratology, derived from the Greek teratos, meaning monster. A teratogen may be defined as any agent that acts during embryonic or fetal development to produce a permanent alteration of form or function. Thus, a teratogen may be a medication or other chemical substance, a physical or environmental factor such as heat or ...

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