Teratogen in Pregnancy: Definition, Exposure & Examples

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  • 0:03 Definition of Teratogen
  • 0:29 Exposure to Teratogens
  • 1:05 Examples of Teratogens
  • 4:54 Lesson Summary
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Lesson Transcript
Instructor: Hilary North

Hilary is a biomedical researcher with a PhD in neuroscience.

Learn what a teratogen in pregnancy is, relevant time lines during gestation, the most common examples, their effects on developing fetuses, and ways to avoid them.

Definition of Teratogen

Basically, a teratogen is an agent that, once in contact with a pregnant mother, will produce a defect in the developing fetus. A teratogen can be either a physical substance or a condition in the mother. The resulting defect can be either a physical abnormality or a functional defect. With this general definition in mind, it's obvious that types of teratogens and their resulting issues can run the gamut.

Exposure to Teratogens

After an egg is fertilized by a sperm, the resulting zygote travels to the uterus and develops into an embryo. Cells begin to divide, increasing the embryo's size, and it migrates from the fallopian tubes towards the uterus, where it eventually settles, implanting in the uterine wall. This does not occur until nearly a week after conception. After implantation, growth of supporting structures such as shared blood vessels begins. Finally, about 2-3 weeks after fertilization, the embryo shares a blood supply with the mother. It's around this time that the embryo can be affected by teratogens.

Examples of Teratogens

The following are examples of common teratogens and the defects they can cause:

Alcohol is one of the most commonly recognized teratogens. Alcohol damages brain cells, which can lead to mental retardation in many children who were exposed during gestation. It can also lead to abnormalities in face and head size, as well as generally slow growth and cause abnormalities in the rest of the body.

Nicotine is another widely recognized teratogen, and pregnant women are strongly encouraged not to smoke. Nicotine exerts its harmful effect on the fetus by constricting the blood vessels, which leads to less blood flow to the baby. Because blood circulating from the mother is the only way the fetus can get oxygen, this leads to hypoxia, or low flow of oxygen, and the fetus effectively suffocates. The result can be low birth weight and even premature birth. These conditions can cause a variety of health problems that may last for the baby's lifetime.

Many illegal drugs, especially the stimulants cocaine and amphetamines, are also teratogenic. These drugs disrupt development of neurons and brain tissue, and babies whose mothers abuse them can be found to have cysts, or hollow spaces, in the brain. If the child survives, learning and behavioral problems often result.

There are also a number of legal prescription drugs that are not safe for pregnant women to use. All drugs approved by the FDA have been studied and assigned a score from A to X. Category A drugs have no effect on a pregnancy. Category D drugs have enough possible effect on a pregnancy that they are avoided. Category X drugs are the most harmful to a developing fetus. Thankfully, most of those aren't on the market, but it's worth being aware of them.

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