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Birth Defects Testing - 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 also can be done as part of an integrated screening test. This test combines the results of the first-trimester tests (first-trimester blood tests and nuchal translucency test) with those of a second-trimester test (the triple or quad screening).

Cell free fetal DNA

The cell free fetal DNA test looks at fetal DNA in a pregnant woman's blood. It can help find genetic problems like Down syndrome or trisomy 18. This test is an option for women who have risk factors for having a baby with certain birth defects. It's not used as a general screening test or for women who are carrying twins.

Diagnostic test

  • Chorionic villus sampling (CVS)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.

WebMD Medical Reference from Healthwise

Last Updated: May 10, 2013
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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