What Is a Birth Defect?
A birth defect is a mental or physical problem that results in an error in the way bone, brain, skin or tissue developed. A disorder may or may not be inherited — that is, passed from parent to child through genes and chromosomes.

Causes of Birth Defects
Some birth defects are inherited. Just as a baby gets certain traits from his or her parents, he or she can get certain diseases or conditions. These types of birth defects are called genetic disorders.

Birth defects also can result from being exposed to harmful things during pregnancy

Prevention
Some birth defects can't be prevented. But you can decrease your risk of some birth defects by taking care of yourself and not being exposed to certain substances.

If you are thinking about getting pregnant, visit your doctor first. Your doctor or a counselor can help you determine your risk of having a baby with birth defects.

If you miss your period or suspect you are pregnant, visit your doctor. Tell your doctor as much as you can about your diet. Be sure to list any prescription or over-the-counter medications and vitamins, herbs or supplements you are taking.

Harmful Agents
A baby can be born with a birth defect because the mother was exposed to infections or harmful substances during pregnancy. Agents that can cause birth defects when a woman is exposed to them during pregnancy are called teratogens.

Infections
Infections are caused by germs that invade the body and then spread.

Medications
Some medications can be harmful to the fetus. If you are taking any medication, talk with your doctor about its use during pregnancy.

Hazards
Some people are exposed to substances that can harm a fetus. Heavy metals, such as mercury and lead, are harmful.

If you think you may be exposed to a harmful agent at work, talk to your employer about it.

Alcohol and Other Drugs
Alcohol use during pregnancy is a leading cause of mental retardation in children. It is not clear how much, if any, alcohol is safe to drink during pregnancy.

Some babies exposed to large amounts of alcohol during pregnancy develop fetal alcohol syndrome.

Many illegal drugs are harmful to the fetus.

Other Disorders
Many disorders are thought to come from a mix of factors (multifactorial). The exact cause is not known.

Testing
Many babies with birth defects are born to couples with no risk factors.

During prenatal care, some tests are offered to all women (screening tests) and some are offered only to those with known risk factors (diagnostic tests). These tests, along with genetic counseling, will help tell patients about their risk of a problem.

No test is perfect. Your fetus may have a birth defect even if a test result is negative.

Screening Tests
Screening tests are done even when a woman has no symptoms or known risk factors.

Screening tests include:

• Blood tests
• Ultrasound exam

The results of a screening test may require further testing.

Diagnostic Tests
Diagnostic tests most often are offered after a screening test raises concerns.

Diagnostic tests include:

• Amniocentesis
• Chorionic villus sampling
• Fetal blood sampling
• Detailed ultrasound exam

The Next Steps
For some tests, it may take a while to receive the results. This time can be stressful.