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Birth Defects Testing (cont.)

First Trimester Tests

Screening tests

The nuchal translucency test and the first-trimester blood tests are often done together in what is called the first-trimester screening.

  • Nuchal translucency test. This test uses ultrasound to measure the thickness of the area at the back of the baby's neck. An increase in the thickness can be an early sign of certain birth defects, such as Down syndrome. This test is often done along with blood tests in the late first trimester. It is not available everywhere, because a doctor must have special training to do it.
  • First-trimester blood tests. These tests measure the amounts of two substances in your blood: beta human chorionic gonadotropin (beta-hCG) and pregnancy-associated plasma protein A (PAPP-A). Beta-hCG is a hormone made by the placenta. High levels may be related to certain birth defects. PAPP-A is a protein in the blood. Low levels may be related to certain birth defects. The doctor looks at the test results—along with your age and other factors—to find out the chance that your baby may have certain problems.

First-trimester tests can be done at around 10 to 13 weeks of pregnancy, depending on the test. Many doctors use a number of tests together, based on what is available.

The first-trimester screening may also be called the combined first-trimester screening or the combined screening. This screening is about as accurate as the quad screening, which is done later in pregnancy.1

First-trimester tests also can be done as part of an integrated screening test. This test combines the results of the first trimester tests with those of a second trimester test (the triple or quad screening).

Diagnostic test

  • Chorionic villus sampling (CVS). Doctors can use this test to look at cells in the placenta. CVS can be done between 10 and 12 weeks of pregnancy. A doctor collects a sample of chorionic villus cells by putting a thin flexible tube (catheter) into your uterus through your vagina or by putting a needle through your belly into your uterus. The test can be used to find chromosomal birth defects such as Down syndrome and family diseases such as sickle cell disease or cystic fibrosis. But it cannot find neural tube defects.

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