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

• Some medicines.
• Street drugs.
• Alcohol.
• Tobacco and nicotine.
• Toxic chemicals.
• Some viruses and bacteria.
• Certain health conditions before or during pregnancy, such as having obesity or uncontrolled diabetes.

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Experts believe that teratogens can begin affecting embryo growth about 10 to 14 days after conception. Conception happens when the egg is fertilized by a sperm. After conception, it takes about 6 to 9 days for the egg to implant in the uterus. After the fertilized egg is attached to the uterus, you and the embryo share a blood supply. Chemicals in your blood can then affect the growing embryo.

Teratogens may affect parts of the body as they are forming. For example, the neural tube closes in the first 3 to 4 weeks of 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 brain and spinal cord. Alcohol affects the brain and spinal cord, so it can cause harm at any time during pregnancy. This is why it is important to not drink alcohol if you are pregnant.

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.

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 between 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 help meet the extra nutritional needs during 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 doctor first. Extra amounts may be harmful.
• Microwave ovens. Microwave ovens use nonionizing radiation. This type of radiation is not teratogenic. Microwaving food while you are pregnant is not known to increase the risk for birth defects or health problems.

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