Period of Vulnerability
The embryo’s development is most easily disturbed during the period when differentiation and development of the organs are taking place. This time interval, which is often referred to as the period of organogenesis, extends from day 15 to day 60 after conception. Environmental influences during the first 2 weeks after fertilization may interfere with implantation and result in abortion or early resorption of the products of conception. Each organ has a critical period during which it is highly susceptible to environmental derangements4 (Fig. 7.12). Often, the effect is expressed at the biochemical level just before the organ begins to develop. The same agent may affect different organ systems that are developing at the same time.