TABLE 8-1 Conditions and Substances that Affect the Developing Brain

Needed for Normal Brain Development

Detrimental or Toxic



Adequate protein and energy


Micronutrients, such as iron and zinc


Adequate gestation

Prenatal infections


Polychlorinated biphenyls (PCBs)

Thyroid hormone

Ionizing radiation

Folic acid


Essential fatty acids

Metabolic abnormalities (excess phenylalanine, ammonia)

Sensory stimulation




Social interaction

Chronic stress

Note: The listed factors are not intended to be exhaustive.

Infectious Disease

Rubella (German measles) is a classic example of an infectious disease that causes harm in utero. Exposure to rubella early in prenatal development affects the organs (e.g., eyes, ears) that are developing at the time that the virus crosses the placental barrier. Because the development of most organs is largely complete by the end of the first trimester, fetal development during the second and third trimesters of pregnancy is relatively more protected from the negative effects of the rubella virus.

The rubella story demonstrates how long it has often taken to recognize that a particular condition or exposure can put the fetus or child at risk. It was widely believed that few diseases were as benign as rubella until 1942, when the first report of the devastating effects of maternal infection during pregnancy was published (Gregg, 1942). One of the puzzles is why the medical community did not figure out the link between maternal rubella and congenital malformations earlier. Some qualities of rubella, which exist in other conditions as well, made it difficult to make the connection (Beswick et al., 1949). For example, it is not always clear that a fetus has been exposed to a particular infectious illness or toxic agent during pregnancy. In the case of rubella, there are many causes of fever, rash, and other symptoms that are seen. To complicate matters further, effects on the developing fetus or child may also be quite variable. For instance, rubella may affect the fetus's eyes, ears, brain, or heart, among other organs. Furthermore, the very idea that the fetus could be vulnerable to harm was novel before the rubella syndrome was accepted. This is now known to be true for many conditions, such as some of those in Table 8-1.

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