Screening Tests for Birth Defects

What are birth defects?

A birth defect is a mental or physical problem that is present at birth. Almost all babies born in the United States are healthy, with only 2-3% being born with a major birth defect (also called a congenital disorder). Most birth defects occur during the first 3 months of pregnancy, but may occur after birth or later in a person’s life.

What causes birth defects?

Birth defects may be caused by genetics or exposure to harmful agents. For about 70% of newborns born with birth defects, the cause is unknown.

Birth defects occur when the heart, kidney, bone, brain, skin, muscle, or other organs do not develop normally, affecting the body’s appearance, function or both. Most birth defects are mild, with a small number severely affecting the baby or causing death. Surgery or other medical treatments may be necessary to correct or improve birth defects.

What is a screening test?

Screening tests are done to determine a mother’s chance of having a baby with a certain birth defect. These tests are performed when there are no symptoms or known risk factors present. A screening test shows an increased risk for having a baby with certain defect and will require additional testing if abnormal results are returned. In most causes, babies with abnormal screening results are born healthy with no birth defects.

Likewise, a baby with normal screening results may be born with a birth defect as some defects can not be tested for. Ask your doctor for a clear explanation of test results and what they mean.

What types of screening tests are available?

First Trimester Screening
The First Trimester Screening test combines a special ultrasound test and blood test to detect signs of Down syndrome, trisomy 18 and heart defects. This new test is performed between 10 and 14 weeks of pregnancy and is not done everywhere. Ask your doctor for details.

Maternal Serum Screening
The Maternal Serum Screening is a blood test screening three or four substances in your blood: Alpha-fetoprotein (AFP), Estriol, Human chorionic gonadotropin and Inhibin-A. Certain levels of these substances can determine a high risk for neural tube or abdominal wall defects, Down syndrome and trisomy 18. This test is performed between 15 and 20 weeks of pregnancy because the levels of some substances can only be accurately read at this time period.

Should I be tested?

All women are offered screening tests during their pregnancy, with diagnostic tests available for abnormal screening test results. A woman may be offered a diagnostic test first rather than having a screening test if she is at high risk of having a baby with a birth defect due to:

  • Age 35 years or older when the baby is due
  • Family or personal history of birth defects
  • Previous child with a birth defect
  • Use of certain medicines around the time of conception
  • Diabetes before getting pregnant