What is any agent that can cause harm to a developing fetus during prenatal development when the mother is exposed?

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 uncontrolled diabetes

How to say it

ter-AT-uh-jehn

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 the 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 to 5 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 two 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 avoid during pregnancy that may cause birth defects. They can answer your questions and help you have a safe pregnancy.

Summary

• Drugs that can cause birth defects are said to be ‘teratogenic drugs’.
• Medical science cannot always predict how exposure to a teratogenic drug will affect a developing fetus.
• It can be dangerous for a pregnant woman to stop taking prescription drugs if she has a medical condition or becomes ill. Without treatment, the health and welfare of both the mother and her unborn baby could be at risk.

This page has been produced in consultation with and approved by:

This page has been produced in consultation with and approved by:

Related information

• The cause of birth defects is often unknown, speak to your GP if you are at increased risk of having a baby with a congenital anomaly.

• Folic acid taken before conception, and during at least the first four weeks of pregnancy, can prevent around seven out of 10 cases of neural tube defects.

• Most cleft palates and cleft lips can be repaired so that appearance and speech develop normally.

• Congenital adrenal hyperplasia (CAH) can affect a child's normal growth and development, including normal growth of the genitals.

• Most children born with cri du chat syndrome have moderate intellectual disability, with varying degrees of speech delay and some health problems.

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