Down Syndrome Screening – Some Details On The Prenatal Test

The prenatal test is a diagnostic Down syndrome screening tool used during pregnancy in order to know if the unborn child is developing normally. The diagnosis of Down syndrome can be made either before the birth (prenatal) or after the birth (postnatal) of the child. Understanding Down syndrome and its causes can help in diagnosing the condition faster.

There are two kinds of prenatal tests used in order to confirm the Down syndrome symptoms.

Down Syndrome Screening: Screening Tests

Every woman has a small degree of risk of having a child with Down syndrome, and this test looks for a possible risk of a giving birth to a child with Down syndrome. However, it should be noted that this test only indicates if the risk of having a child with Down syndrome is high or low, and does not indicate if the child will be born with Down syndrome or not.

Usually, Down syndrome screening tests are carried out either in the first trimester of the pregnancy or in the second trimester. The most common Down syndrome screening tests are maternal serum testing and ultra sound (nuchal translucency) testing. These tests do not pose any risk either to the mother or the unborn child.

Maternal Serum Testing

The serum test measures the levels of the hormone beta human chorionic gonadotropin (beta-HCG), the levels of alpha fetoprotein (AFP), and the levels of pregnancy associated plasma protein A (PAPP-A) in the blood. These are produced by the placenta and the developing child. If the child has Down syndrome, the hormone and the protein levels are likely to be abnormal. The risk factor is calculated based on the blood test results, the stage of pregnancy, and the age and weight of the mother.

Ultrasound (Nuchal Translucency Testing)

This kind of ultrasound Down syndrome screening is carried out between 11 to 14 weeks of pregnancy. The fluid below the skin behind the child’s neck (nuchal translucency) is measured using ultrasound. Children with Down syndrome have more fluid in this area when compared to normal children.

down syndrome screening
During down syndrome screening, the fluid in the back of the child’s neck is measured.

If both these screening test results indicate a high risk of having a child with Down syndrome, diagnostic tests are advised for confirmation of the results.

Down Syndrome Screening: Diagnostic Tests

There are two kinds of tests available for diagnosing Down syndrome – Chorionic Villus Sampling and Amniocentesis. By analyzing the overall genetic blueprint of the cells from the child and the placenta, these tests can confirm (with a surety of close to 99%) whether the child would be born with Down syndrome. However, there is a possibility of miscarriage after the tests are carried out.

Although the reasons behind these miscarriages aren’t clearly understood, it is believed that there could be amniotic fluid leakage or infection caused during both these diagnostic procedures.

Chorionic Villus Sampling

This test is carried out between 11 to 14 weeks of the pregnancy, by taking a small tissue sample from the Chorionic Villus region of the placenta with the help of a small needle. This test is used to check if the child is carrying an abnormal chromosomal number. There is 1- 2% risk of miscarriage associated with the procedure.


This test is carried out between 15 to 18 weeks of the pregnancy, by taking a sample of the amniotic fluid that’s present in the uterus and surrounds the unborn child. The sample, which contains cells from the unborn child, is drawn for testing with the help of a fine needle.

By analyzing the genetic material in the sample, one can determine if the child has Down syndrome or not. There is a 1% risk of miscarriage after an Amniocentesis is carried out.

If the prenatal Down syndrome screening results turn out to be abnormal, after proper counseling, one can decide whether to continue and prepare for the birth of the child (with Down syndrome) or end the pregnancy.

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