Birth defects affect 3% of pregnancies in the United States. Screening and diagnostic tests during pregnancy can identify many birth defects. Parents can take critical steps to help prevent certain defects.

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Birth defects are common. According to the Centers for Disease Control and Prevention (CDC), birth defects affect 1 in 33 babies born in the United States each year.

The cause of many birth defects is unknown. However, other defects are a result of genetic factors, environmental exposure, or related to certain risk factors.

Preparing for pregnancy can help reduce your risk of birth defects.

Learn more about birth defects.

Birth defects are changes that happen while the fetus develops and are present when the baby is born. Defects can occur on any body part, both internally and externally. They may affect how the body looks or works. Some birth defects are mild, while others are severe.

Most birth defects happen during the first 3 months of pregnancy. Doctors can identify some defects before birth, but others are found after your baby is born or later in life.

There are generally no signs and symptoms during pregnancy that indicate a fetus has a birth defect.

Most birth defects that are diagnosed prenatally, or during pregnancy, are discovered during routine exams or screening tests to evaluate the health of the fetus, such as physical examinations and ultrasounds.

There are several ways a doctor can diagnose birth defects during pregnancy. These include:

Screening tests

Screening tests are the first step in looking for birth defects during pregnancy. They include:

Screening tests determine whether your pregnancy is at high risk of a birth defect but do not tell whether the baby is affected. Your healthcare professional will offer diagnostic tests if screening test results are not typical.

Diagnostic tests

Tests that may be used to diagnose birth defects include amniocentesis and chorionic villus sampling (CVS). Which test is offered depends on how far along you are in pregnancy.

CVS tests a sample of placental tissue. Amniocentesis tests amniotic fluid. Both tests analyze your baby’s chromosomes.

After delivery

There are ways to diagnose birth defects after a baby is born. The following tests may be performed depending on which birth defect your doctor suspects:

Genetic changes cause some birth defects, such as Down syndrome and cystic fibrosis. Parents pass on some defects, while others result from chromosome changes at conception. But genetics causes only a minority of defects.

Environmental factors are another cause of birth defects, such as:

The age of the birthing parent (or egg donor if undergoing IVF with a donor egg) is a risk factor for birth defects. Pregnancy after age 35 increases the risk of chromosomal abnormalities such as Down syndrome.

Most birth defects have unknown causes. There’s likely a complex interaction of environmental and genetic factors involved.

There are things you can do to decrease the chances of birth defects.

Before pregnancy

Having a checkup with your prenatal care practitioner before getting pregnant is recommended. Here are things to discuss at your appointment:

  • Lifestyle: Discuss any substance use or environmental exposures. This is the time to stop smoking and using alcohol or other substances.
  • Chronic health conditions: Certain conditions, such as diabetes and obesity, increase the chance of birth defects.
  • Vaccinations: Make sure you are up to date on all vaccinations.
  • Medications and supplements: Sometimes medications need to be changed to safer options for pregnancy.
  • Weight: Maintaining a moderate weight before pregnancy can lower the risk of birth defects.
  • Folic acid: Folic acid helps prevent neural tube defects such as spina bifida. Taking a daily multivitamin with folic acid before you get pregnant may help prevent neural tube defects. Check with your healthcare professional about the ideal dose for your situation.

During pregnancy

To help prevent birth defects during pregnancy, you can:

  • get regular prenatal care
  • check with your healthcare professional before starting any new medication or supplement
  • avoid harmful substances
  • avoid travel to areas with Zika
  • prevent toxoplasmosis by avoiding contact with cat feces or contaminated dirt
  • protect yourself from cytomegalovirus (CMV) infection

If your baby is diagnosed with a birth defect while you’re pregnant, you will likely see a specialist called a maternal-fetal medicine (MFM) doctor. They can work with you to develop a plan based on your baby’s specific needs. Sometimes this includes additional monitoring or surgery.

Some birth defects diagnosed during pregnancy are severe or terminal conditions and result in fetal death or termination of the pregnancy. Your care team can provide the answers and support you and your family need during this time.

If my first baby had a birth defect, would my next baby also have the same defect?

It depends on which birth defect your other child has. In some cases, you may have an increased risk of having another baby with the same or similar birth defect.

Genetic counseling can help you know your risk.

Which birth defects are the most preventable?

Taking folic acid prevents neural tube defects. Maintaining a moderate weight can reduce the risk of heart defects.

You can completely prevent fetal alcohol spectrum disorders by avoiding all alcohol during pregnancy.

Can birth defects be treated or corrected?

Birth defects vary in their severity and treatment options. Medical interventions, surgeries, or devices can treat or correct some defects. Not all birth defects can be fully resolved.

Birth defects occur during fetal development. They can internally or externally affect the body. Some defects can be detected during pregnancy, while others are identified after birth.

Genetic changes and environmental factors may contribute to birth defects. Not all birth defects can be prevented, but seeking early prenatal care, taking folic acid, and not drinking alcohol, smoking, or using other harmful substances can decrease the chances of birth defects.