Diagnosing Down Syndrome During Pregnancy

Down syndrome can be diagnosed prenatally through a combination of screening tests that are available to all pregnant women.

There are some individuals that are identified as being at risk for a particular genetic problem. In particular, women over the age of 35 years of age are more at risk of having a baby with Down syndrome than women who are younger. Research has shown that a pregnant woman of 35 years runs a 1in 274 risk of having a baby with Down syndrome, while a pregnant woman of 25 years runs a much lower risk of 1 in 887 of having a baby with Down syndrome. A woman who gets pregnant at age 45 will have a 1 in 22 risk of producing a baby with Down syndrome and a woman of 49 a 1 in 8 risk.

Prenatal Diagnosis

Amniocentesis

Amniocentesis is a test that is generally performed between the 16^th and 18^th weeks of pregnancy.

During this procedure a sample of amniotic fluid is obtained, and analyzed. Amniotic fluid contains fetal cells that can be grown and examined for chromosome abnormality.[

Chorionic Villus Sampling

Chorionic villus sampling can detect chromosome abnormalities and is usually offered to women who will be 35 years of age or older at the time of delivery. This procedure has a 2-3% risk to the fetus and, therefore, is usually reserved for those women who are a particular risk.

During this procedure, a probe is inserted through the cervix and a villa, which attaches the placenta to the uterus wall, is removed and analyzed

Ultrasound Scanning

The technique of ultrasound scanning has become more sophisticated and its use has been directed at detecting the presence of Down syndrome in a developing fetus.

The head of a fetus can be examined and it is possible to identify the characteristic shape. It is also possible to look for a thickened skin-fold at the back of the neck, and to see if the thigh- bone (femur) is shorter than would be expected.

Combine these results with ultrasound detection of heart abnormalities, which are common in Down syndrome, this technique is about 80% accurate.

Ultrasound screening for Down syndrome cannot be performed until the fetus has developed sufficiently, usually after the 12-14 week stage.

Sources:

The Down syndrome Handbook-A Practical Guide for Parents and carers by Dr. Richard Newton in association with the Down Syndrome Association.

Babies with Down Syndrome - A New Parents' Guide (2^nd edition) edited by Karen Stray-Gunderson.

www.labcorp.com/genetics/prenatal_testing/index.html.www.labcorp.com/genetics/genetic_disorders/down_syndrome.html