Teratogenesis is a process that causes birth defects or malformations in an embryo or foetus. Teratology is the study of the causes and underlying mechanisms leading to birth defects or malformations. These may include disorders without any obvious structural malformations, such as intellectual disabilities. A teratogen is a substance (from outside the body) that causes birth defects or malformations. Examples of teratogens include medicinal drugs, such as thalidomide; environmental toxins, for example cadmium as well as environmental pollutants, including pesticides and endocrine‐disrupting compounds. Other causes of teratogenesis include viruses, for example rubella and Zika virus; physical compression in utero and poor diet. Animal models are used to study the mechanisms by which teratogens result in birth defects or malformations, and these studies can also give insights into normal development. The study and understanding of teratogenesis is also essential for making safer and more targeted therapeutic drugs.

Key Concepts

  • Teratogenesis is the production of birth defects or malformations by external agents.
  • Teratology is the study of the mechanisms that give rise to birth defects or malformations.
  • There are many factors that can result in teratogenesis, including medicinal and recreational drugs, viral and bacterial infections and poor maternal health.
  • Teratogenesis is studied in animal models, for example mouse, chicken and rabbit embryos.
  • Understanding whether a chemical compound has teratogenic side effects is essential to ensure drug safety.
  • Many teratogens (agents that cause teratogenesis) act between weeks 2 and 8 of embryonic development, a period also known as the ‘critical period’ of development when the majority of tissues and organs are forming and being patterned, for example the limbs.

Keywords: thalidomide; animal models; the 3Rs; teratogen; time‐sensitive window; birth defects

Figure 1. Outward damage caused by thalidomide exposure of human embryos at different times during pregnancy. Thalidomide caused outward damage (e.g. to the limbs, ears and eyes) between day 20 and day 36 of embryonic development. Note that there is generally more widespread damage the earlier the exposure to thalidomide occurs in the time‐sensitive window. The action of thalidomide falls within the embryonic ‘critical period’ which is between 2 and 8 weeks of development when all the major tissues and organs are forming and these tissues are most sensitive to disruption. Reproduced from Vargesson © Wiley Periodicals, Inc. under the terms of the Creative Commons Attribution License.


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Further Reading

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Vargesson, Neil, and Fraga, Lucas(Dec 2017) Teratogenesis. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0026056]