Disruption is defined as a morphologic or structural anomaly of an organ, part of an organ, or a larger region of the body resulting from the extrinsic breakdown of, or interference with, an originally normal conceptus or developmental process. Disruptions tend to be sporadic occurrences (Figure 10.1 and Tables 10.1 to 10.6).

TYPES OF DISRUPTIONS AFFECTING MORPHOGENESIS OF THE DEVELOPING EMBRYO AND FETUS

1. ■ Radiation

2. ■ Hyperthermia

3. ■ Infection

4. ■ Teratogenic drugs

5. ■ Metabolic

6. ■ Vascular

7. ■ Amnion disruption

TERATOGENIC DISRUPTIONS

Growth and development of the embryo can be adversely affected by a wide variety of environmental agents (teratogens). Teratogens include intrauterine infections, various chemical agents and medications, and maternal metabolic disorders.

The first two weeks of life that is, the time before organogenesis appears to be a relatively safe time for the embryo regarding teratogenic exposure. The next 45 days, however, are especially dangerous for it is during this period that most organs develop. After an organ has developed, unless there is disruption, the teratogen cannot cause a malformation. The same teratogen can cause different defects at different times of exposure.

Most teratogens produce a characteristic, clinically recognizable, pattern of abnormalities.

RADIATION EMBRYOPATHY

In utero radiation is associated with microcephaly, mental retardation, and stunted growth, especially in infants exposed between the 8th and 15th weeks of gestation, and there is an increased incidence of leukemia.

HYPERTHERMIC EMBRYOPATHY

Hyperthermia, a body temperature of at least 38.9°C, is an antimitotic teratogen when the fetus is exposed to a high temperature between the 4th and 16th week of gestation (Figure 10.2 and Table 10.7).