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Inherited Disorders and Birth Defects

AFT test failure

01/09/2007

Question:

I am 32 and pregnant with my first child (I had two previous miscarriges). I was told by my OB/GYN that I had failed the triple check test, and had a 1 in 25 chance of having a baby with downsyndrome. Her immidite questions was if I wanted to keep my baby as the risk was very high. Amniocentesis is a risky option for me to consider. What are my true chance of having a child with down syndrome?

Answer:

The screening test you had, a triple check, looks at 3 types of proteins that have been found to be associated with chromosome problems; the most common one is Down syndrome, also called trisomy 21. Because this blood test is a screening test, not a diagnostic test - it can only tell you about your potential chance or risk to have a baby with Down syndrome. It cannot tell you for sure if the baby will have Down syndrome.

In your case, if the doctor said your chance to have a baby with Down syndrome was 1 in 25, he means that out of 25 babies, one would have Down syndrome, the others would not. The only way to know for sure if the baby has Down syndrome is to do an amniocentesis – inserting a thin needle into the amniotic sac, obtaining fluid from around the baby which contains the baby’s cells and doing a chromosome analysis (a diagnostic test). This is the only way to tell you what your true chance is to have a baby with Down syndrome.

However, you are correct; there is a chance of complications that can lead to a miscarriage following amniocentesis. Doctors usually say the risk is about a half of a percent (0.5% or 1 in 200), but a recent study suggests that the risk of miscarriage may be less than this, about 0.06% or 1 in 1600 pregnancies.

You could also ask your doctor about having a level II ultrasound done to look for “markers” that are associated with Down syndrome. These are findings that are not abnormalities, but are clues that perhaps the baby has Down syndrome. This may give you some more information which would be helpful to you in your decision making process about having the amniocentesis. Regardless, it is your decision as to whether or not you have the amniocentesis.

I would also recommend that you ask your doctor about a referral to talk to a genetic counselor or geneticist to discuss these issues in depth with you. This is an area in which they have a lot of expertise. You can locate a genetics center near you through the National Society of Genetic Counselors Resource Center website below.

Related Resources:

National Society of Genetic Counselors Resource Center

For more information:

Go to the Inherited Disorders and Birth Defects health topic, where you can:

Response by:

Anne   Matthews, RN, PhD Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University