Adverse pregnancy outcome: sensitive periods, types of adverse outcomes, and relationships with critical exposure periods.

A wide variety of agents has been demonstrated to be capable of affecting the fetus in utero. Certain generalizations can be made concerning these teratogens. Two of the most important of these principles are the specificity of the agent and the time during gestation of the exposure. Although noticeable adverse effects are structural malformations, there are numerous functional malformations, such as lower intelligence and poor reproductive outcome, that may follow exposure to these agents. There is some evidence that future behavior may be affected by in utero teratogen exposure; however, this field has been infrequently investigated and no firm conclusions can be drawn.