425 899 2200 (Kirkland office); 425 688 8111 (Bellevue office)

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My test has come back positive for Trisomy 18

Does an abnormal (or “positive”) test result mean the baby has a birth defect?

NO!  For example, a result of 1 in 100 chance of trisomy 18 means that 99 out of 100 times the baby does NOT have trisomy 18.  Most women with abnormal results will have healthy babies.  Multiple marker screening tests cannot diagnose a birth defect.  Abnormal test results mean only that the chance that the baby has trisomy 18 is higher and that parents should be offered further tests to try to find the cause of the abnormal blood chemical levels.  In most cases, an abnormal test result does not turn out to be because of a problem with the baby, and further testing can confirm that. 

What else could an abnormal result mean?

Normal variation.  Some healthy babies produce levels of AFP, HCG, and estriol in the pattern seen more frequently in babies with trisomy 18. (***This abnormal pattern of blood chemicals cannot be explained by mistakes in dating the pregnancy.)

What happens now?

Most women who have an abnormal multiple marker screening test result are referred to a specialized center, such as Eastside Maternal-Fetal Medicine Associates, for further evaluation.  The first part of the visit is spent with a genetic counselor, who spends as much time as needed answering any questions parents have.  The genetic counselor will review the abnormal test results and discuss the follow-up tests available to the parents.  A family and pregnancy history is taken as well, to identify other, unrelated, risks to the baby.  High-resolution ultrasound and amniocentesis may be done, based on the decisions made by the parents.  A high-resolution ultrasound may identify obvious birth defects but cannot diagnose trisomy 18.

Where can I get more information?

Your primary pregnancy healthcare provider may be able to give you more information.  You may want to make an appointment with a genetic counselor to get additional details or help with decision-making.  

If you live in the Seattle/King County area, and you would like to talk more about these tests and making a decision please call us at (425) 688-8111 ( Bellevue ) or (425) 899-2200 ( Kirkland ) to schedule an appointment.

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Last modified: August 31, 2008