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  • Developmental toxicology encompasses the study of pharmacokinetics, mechanisms, pathogenesis, and outcomes following exposure to agents or conditions leading to abnormal development.

  • Developmental toxicology includes teratology, or the study of structural birth defects.

  • Gametogenesis is the process of forming the haploid germ cells: the egg and the sperm.

  • Organogenesis is the period during which most bodily structures are established. This period of heightened susceptibility to malformations extends from the third to the eighth week of gestation in humans.

  • Teratology is the study of abnormal structural development.


With the development of highly sensitive tests that can detect pregnancies shortly after fertilization, recognized pregnancy loss increased to as much as 60% to 70%. Estimates of adverse outcomes include postimplantation pregnancy loss, 31%; major birth defects, 2% to 3% at birth and increasing to 6% to 7% at 1 year with continuing diagnoses; minor birth defects, 14%; low birth weight, 7%; infant mortality (prior to 1 year of age), 1.4%; and abnormal neurological function, 16% to 17%. Of over 4100 chemicals tested for teratogenicity, a much smaller number, about 35 to 40 chemicals, chemical classes, or conditions (Table 10–1), have been documented to be developmentally toxic in humans.

TABLE 10–1Human Developmental Toxicants

Maternal Rubella Infection

In the 1940s, an epidemic of rubella virus infection in Australia was linked to congenital malformations including eye, heart, and ear defects, and mental retardation. Heart and eye defects were associated with maternal infection in the first 2 months of pregnancy, while hearing and speech defects and mental retardation occurred with infection in the third month. Rubella is now uncommon in developed countries due to widespread vaccination, but recent outbreaks have been reported.



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