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Medical Genetics: Teratogens

What is a teratogen?

A teratogen is something that can cause or raise the risk for a birth defect in a baby. They are things that a mother may be exposed to during her pregnancy. Teratogens include:

  • Some medicines

  • Street drugs

  • Alcohol

  • Tobacco

  • Toxic chemicals

  • Some viruses and bacteria

  • Certain health conditions, such as obesity or uncontrolled diabetes before or during pregnancy

How to say it


The riskiest times of pregnancy

Experts believe that teratogens can begin affecting a baby growing in the womb about 10 to14 days after conception. Conception is when a woman’s egg is fertilized by a man’s sperm. After conception, it takes about 6 to 9 days for the egg to implant in the uterus. Once the fertilized egg is attached to the uterus, the mother and embryo share a blood supply. Chemicals in the mother's blood can then affect the growing baby.

As a baby grows in the womb, teratogens may affect parts of the baby’s body as they are forming. For example, the neural tube closes in the first 3 -4 weeks of the pregnancy. During this time, teratogens can cause neural tube defects, such as spina bifida. Some organs are sensitive to teratogens during the whole pregnancy. This includes the baby's brain and spinal cord. Alcohol affects the brain and spinal cord, so it can cause harm at any time during pregnancy. This is why you should not drink alcohol if you are pregnant.

How are teratogens known?

Researchers have 2 ways of finding out if a substance is a teratogen. They are:

  • Animal studies. Animal studies are the main way to find out if a medicine or other substance is safe during human pregnancy.

  • Observations from human exposure. This means reports of problems about a substance over time.

What are nonteratogenic agents?

Certain things have been shown to not cause birth defects. These are called nonteratogenic agents. These include:

  • Spermicides. These are chemicals that kill sperm to prevent pregnancy. These chemicals are found in products for birth control, such as gels, creams, and foams, and on some condoms. Studies have shown no link with the use of spermicides and any increased chance for birth defects.

  • Acetaminophen. This is a common ingredient in some pain medicines. There has been no link between birth defects and taking acetaminophen at the advised dose during pregnancy.

  • Prenatal vitamins. Prenatal vitamins are prescribed to pregnant women to help meet the extra nutritional needs of pregnancy. When used at the recommended dose, they don’t increase the risk for birth defects. But don’t take any extra vitamins, minerals, or herbal supplements without talking with your healthcare provider first. Extra amounts may be harmful.

  • Microwave ovens. Microwave ovens use nonionizing radiation. This type of radiation is not teratogenic. Microwaving food while pregnant is not known to increase the risk for birth defects or health problems.

Talking with your healthcare provider

If you’re pregnant, talk with your healthcare provider about things to stay away from during pregnancy that may cause birth defects. They can answer your questions and help you have a safe pregnancy.