Recent progress in teratology. A survey of methods for the study of drug actions during the preimplantation period.

To evaluate the effects of drug treatment during the first days of pregnancy new approaches have been developed which allow the study of teratogenic effects already before and around implantation, during organogenesis, and at term. The procedures used for the culture of preimplantation mouse embryos that were either pretreated in vivo or previously untreated and exposed to a toxic agent in vitro are presented in particular detail. In addition, an example is given which shows that it is possible to detect a DNA repair mechanism in preimplantation embryos maintained in vitro. The techniques of embryo transplantation and in vitro cultivation of embryos beyond implantation are outlined. The importance of the two methods in teratological research on embryos pretreated either in vivo or in vitro is discussed. Also presented are a survey of the literature and recent data obtained with rats and mice from our laboratory which prove that the action of drugs on the embryo and mother during the preimplantation period are more complex than is generally assumed.