Teratogen update: paternal exposures-reproductive risks.

The potential of many drugs and chemicals to cause prenatal harm is well-established. The types of effects seen vary and include spontaneous abortions, stillbirths, congenital malformations present at birth, and conditions detected only months to years after birth. Most studies designed to determine whether agents cause malformations have examined the effects of exposure of the embryo or fetus at various times during gestation. Thus the effects studied are maternallymediated. Despite these drug studies and those on other causes of birth defects, such as chromosomal abnormalities, the cause of approximately 60% of congenital malformations is unknown. Fewer studies have examined the possibility that exposure of the male to a drug or chemical could lead to abnormalities in his offspring, i.e., be maleor paternally-mediated. Over the last 10–20 years, there has been more interest in addressing this question as increasing numbers of patients and workers are exposed to agents that alter fertility. A number of animal studies as well as more recent human epidemiological studies have demonstrated that exposure of males to various agents can result in abnormal reproductive, pregnancy, and/or progeny outcomes (Olshan and Mattison, ’94).