Women's Healthcare Topics

Prenatal Screening for Down Syndrome

Reviewed by James Brann, M.D.

Screening for Down Syndrome

Screening tests for Down syndrome are voluntary, but the American College of Obstetricians and Gynecologists suggest that the testing be offered to all pregnant women without regard to age.

There are three different screening tests available for Down Syndrome. One screening test is done in the first trimester and is typically performed at 11 to 13 weeks of pregnancy. The genetic screening test involves drawing your blood and doing an ultrasound of the baby (Nuchal Translucency Ultrasound).

The second screening test is done later in your pregnancy and it only requires a sample of your blood. It is done during the second trimester of pregnancy, typically at 15 to 18 weeks.

The third screening test combines results from both tests done during the first and second trimesters. These tests involve two samples of your blood, and an ultrasound called a nuchal translucency ultrasound.

Video: Advances in Non-invasive Prenatal Testing

The three different tests only will tell you if you are at an increased risk for Down syndrome or not. Therefore, if you have a positive screening test it only indicates an increased risk of having a baby with Down syndrome. Not that your baby has Down Syndrome. To tell if your baby will really have Down syndrome you have to undergo further (diagnostic) testing.

Nuchal Translucency Ultrasound

The nuchal translucency ultrasound, also called a nuchal fold scan, is a prenatal screening test that assesses your baby's risk for Down syndrome.

This prenatal test uses an ultrasound scan to measure the clear space in the tissue in the back of your baby's neck to check for any excess fluid that may have collected there. Babies with abnormalities tend to have more fluid in the back of their neck than normal babies.

This screening test is considered to be 80 percent accurate. A nuchal fold scan will not give you a diagnosis, but it can tell you if your baby is at high risk for a chromosomal defect. An amniocentesis and chorionic villus sampling (CVS) will be able to give you more definite answers.

Two diagnostic tests are available to tell if your baby has Down syndrome

Learn about the three different screening tests available for Down Syndrome.

Chorionic villus sampling (CVS) — Chorionic villus sampling (CVS) is performed in the first trimester of pregnancy. The test is performed between 10 and 13 weeks of pregnancy. This test samples placental tissue which is done in the office. Chorionic villus sampling has a small risk of miscarriage, about 1 miscarriage for every 100 procedures. A doctor performs a CVS procedure (some women say it's kind of like getting a pap smear) to obtain a tiny sample of CV (chorionic villi) from a baby's placenta on the wall of the uterus. It's not as scary as it sounds, and it usually takes only a couple of minutes for the doctor to get the actual sample.

Learn about the amniocentesis test available for Down Syndrome.

Amniocentesis — Amniocentesis is performed later in your pregnancy, around your second trimester (after 14 weeks of pregnancy). Amniocentesis has a smaller risk of miscarriage then Chorionic villus sampling. Amniocentesis has less than 1 miscarriage for every 200 procedures performed. A highly trained doctor (Perinatologist), using safe ultrasound technology, employs a very fine needle to take a very small sample of amniotic fluid from your uterus, via your abdomen. If you would like you can receive a local anesthetic beforehand, but some women don't require any pain relief.


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