Elements of Teratology

Birth defects are not a rare phenomenon, and, in most cases, are not related to environmental agents. A baseline risk for malformation of 1-3% is commonly used as a reference frame for evaluating the teratogenic risk of environmental exposures. Environmental factors that have a teratogenic potential include drugs, chemicals, infections, and physical factors such as ionizing radiation. Most environmental agents were not found to have teratogenic potential, and among the drugs that were proven to be teratogenic only few, such as thalidomide and systemic retinoids, exhibit increased risk for malformation of above 20% when exposure occurred in the sensitive period. Despite the fact that only a handful of drugs and other exposures have proven to be teratogenic, women, and in many cases health providers as well, tend to overestimate teratogenic risk. In many cases, overestimation of risk may cause women to discontinue essential medications or alternatively to terminate wanted pregnancies. Ultrasound can detect a large number of structural anomalies, including many of those reported to be secondary to exposure to potentially teratogenic agents. Therefore, teratogen risk counseling needs to promote evidence-based rather than fear-based decision-making.