• 1st Trimester Genetic Risk Assessment
• Maternal Screening
• Chorionic Villous Sampling
• Genetic Amniocentesis
• Cystic Fibrosis Carrier Screening
• Integrated Prenatal Screening

1st and 2nd Trimester Genetic Risk Assessment

The First Trimester Prenatal risk assessment is a screening test for pregnant women between 10 and 14 weeks of pregnancy. The test will help detect Down syndrome and trisomy 18 by identifying those who may be at an increased risk for these conditions. If at increased risk, you may be offered genetic counseling and possibly additional testing to rule these problems out.

What Does the First Trimester Prenatal Screening Test Measure?
The First Trimester Prenatal Screening combines the use of:

1. An ultrasound examination to measure the amount of fluid accumulation behind the baby’s neck (nuchal translucency). This ultrasound must be performed by individuals who are specially trained because it is very easy to misinterpret this measurement.
2. A laboratory test performed on the mother’s blood to measure the levels of two proteins normally found in the blood of all pregnant women
   • Free ß-hCG (free beta-human chorionic gonadotropin)
   • PAPP-A (pregnancy associated plasma protein-A)

Combining the blood test with the neck measurement can determine a specific risk that the pregnancy may be affected by Down syndrome or trisomy 18. This test will detect approximately 90% of these pregnancies.

What is Down Syndrome?
In each of our cells, we have 46 chromosomes (23 from the mother and 23 from the father). They give instructions for our development. Down syndrome results when there is an extra number 21 chromosome (three, instead of a pair). Any woman, at any age, can have a baby with Down syndrome, although the risk increases with the age of the mother. People with Down syndrome usually have mild to moderate mental retardation, as well as other medical problems.

What is Trisomy 18?
Trisomy 18 is a severe chromosome abnormality that causes multiple birth defects and profound mental retardation. Few babies with Trisomy 18 survive into childhood. Trisomy 18 results when the fetus has three, instead of the normal two, copies of chromosome 18. Like Down syndrome, the chance to have a pregnancy affected with trisomy18 increases with increased maternal age.

What does it mean if my screen is "Positive"?
About 5% of women will have a "positive" screen. This increase in risk does not mean the baby has a chromosome abnormality. It simply indicates that further tests need to be considered. The options for further testing may include ultra sound examination and CVS or amniocentesis for fetal chromosome analysis. These additional tests will accurately diagnose Down syndrome, Trisomy 18 and the vast majority of other chromosome abnormalities.

Remember that prenatal screening risk assessment is not a diagnostic test. It cannot tell you whether your unborn baby has or doesn’t have a problem. It will simply tell you the odds (chance) that the baby has a problem. Keep in mind that the vast majority of women with "screen positive" results do not have babies with Down syndrome or trisomy 18.

What does a "Negative" test result mean?
A negative result indicates that the risk that the fetus has Down syndrome or trisomy 18 is not increased compared to that of a 35 year old woman. However, a negative result does not completely eliminate the possibility that the fetus may have Down syndrome, trisomy 18, or other chromosome abnormalities. First trimester prenatal screening will detect about 85% of baby’s with Down syndrome and 90% of those with Trisomy 18. This means that it will miss about 10-15% of affected babies.

In addition, first trimester screening does not screen for neural tube defects (failure of complete closure of the spinal column during development) or other types of open defects. A second trimester blood test for alpha-fetoprotein (AFP) or ultrasound examination should be considered.

Why consider First Trimester Genetic Risk Assessment?
This testing is not invasive and provides risk information early in the pregnancy thus reducing parent’s anxiety about the health of their baby as early as possible. In the event of an increased risk, it allows more time for further diagnostic tests and more options for subsequent pregnancy management. In addition, the first trimester screening protocol described here offers a detection rate higher than that of second trimester serum screening.

When should this testing be performed?

10 weeks 3 days ­ 12 weeks 6 days
1st trimester blood screen (free Beta/PAPP-a)

11 weeks 0 days ­ 13 weeks 6 days
ultrasound nuchal translucency (NT) measurement

15 weeks 0 days ­ 20 weeks 6 days
2nd trimester blood screen (AFP, E3, HCG, and Inhibin A)

10 weeks 0 days ­ 13 weeks 6 days
Chorionic villus sampling if indicated

16 weeks ­ 18 weeks
Amniocentesis if indicated

18 weeks ­ 23 weeks
Level III fetal anatomy scan if indicated

20 weeks 0 days ­ 22 weeks 6 days
fetal echocardiogram if indicated
(suspected heart defect on previous anatomy scan)

What is a Genetic counselor?
A genetic counselor is a master’s level specialist trained to provide information and support to families or individuals and prospective parents. The genetic counselor will take a family and pregnancy history, assess your risk factors and provide you with information about your options for screening and prenatal diagnosis. The genetic counselor will be able to help you make decisions about whether or not to have testing and which testing is right for you.

How can I get more information?
If you have questions or would like more information about prenatal screening please call the Prenatal Genetics and Fetal Therapy Program at (206) 598-8130.

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Last Updated:
4/12/07