Pregnancy Screening - Down Syndrome Ultrasound vs. Invasive Tests

Jun 9, 2010
Victoria Nicks

Pregnancy Screening for Birth Defects: Ultrasound - Stock Xchng Image by memoossa

Pregnancy screening can help determine whether a fetus has Down syndrome. Ultrasound testing is both less dangerous and less conclusive than amniocentesis.

Pregnancy can be a stressful time for a mother-to-be with the risk factors for having a Down syndrome baby. Parents that decide to pursue pregnancy screening options to detect Trisomy 21 in their baby may need to choose between non-invasive ultrasound testing, or the more invasive amniocentesis.

Birth Defects: Trisomy 21

Trisomy 21 is the name for the extra chromosome that causes Down syndrome. The extra chromosome causes physical differences, developmental delays and a tendency toward certain health problems. This condition is incurable, but testing during pregnancy gives parents the chance to prepare for the unique needs of a child with birth defects, as well as identifying any specific abnormalities that require medical care.

Down Syndrome Screening via Ultrasound

Initial Down syndrome screening is done through the use of ultrasound imaging. Although there are multiple physical markers that can be used to identify a child with Trisomy 21 on an ultrasound, the nuchal fold (at the base of the neck) is one of the more accurate measurements. A fetus with Trisomy 21 often has more fluid in the neck than usual, which makes the nuchal measurement larger.

This test, known as a nuchal translucency screening, is non-invasive and poses no risks to the mother or baby. Although it is not conclusive, the combination of risk factors and other markers with the size of the nuchal fold can be helpful in diagnosing Down syndrome before birth.

Amniocentesis Testing

Amniocentesis testing can be used to diagnose genetic problems and other birth defects, as well as to check the lung development of the baby. During this procedure, the doctor inserts a long needle into the abdomen to pierce the amniotic sac. A sample of the amniotic fluid is withdrawn through the needle, and tested for the presence of genetic disorders or other indications of birth defects.

Amniocentesis testing may be painful for the mother, due to pain during the procedure and cramping afterward. In addition, amniocentesis can cause side effects including vaginal bleeding, leakage of amniotic fluid and miscarriage. There is also a risk of infection, or injury to the baby during the procedure. The results of this test are conclusive, however, and can provide a definitive diagnosis for concerned parents.

Pregnancy Screening for Down Syndrome

Undergoing pregnancy screening for Down syndrome typically starts with an evaluation of risk factors, combined with ultrasound results. Pregnant women that appear to be carrying a Down syndrome baby may then choose to undergo amniocentesis testing for more conclusive results, or to wait until giving birth to find out for sure. Obstetricians are able to advise their patients, based on test results and other factors.

For more information about Down syndrome and pregnancy, read Down Syndrome Symptoms During Pregnancy and Risk Factors for a Down Syndrome Pregnancy.

To learn more about the outlook for people with Down Syndrome, read Down Syndrome Life Expectancy.

For more information about rare forms of Trisomy 21, read Translocation & Mosaic Down Syndrome - Rare Genetic Birth Defects.

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References:

California Department of Public Health, Genetic Disease Screening Program.Nuchal Translucency (NT) Practitioner Manual. (2009). Retrieved June 8, 2010.

Wang, J. OB/GYN News. Fetal Markers Seen on Ultrasound Can Help Assess Down Syndrome Risk. (2001). Retrieved June 8, 2010.

U.S. National Library of Medicine. Amniocentesis.Retrieved June 8, 2010.

American Pregnancy Association. Down Syndrome: Trisomy 21. (2008). Retrieved June 8, 2010.