Frequently Asked Questions

What is first trimester screening (FTS)?

This test is designed to identify pregnancies at an increased risk for Down syndrome and trisomy 18 early in the pregnancy. It does not diagnose either condition but provides an adjustment of a woman’s age-related risk. For example, a 35 year old woman has a risk of approximately 1/270 for Down syndrome. FTS will provide an approximate risk value either equal to, higher (e.g., 1/15) or lower (e.g., 1/1000) than 1/270. Many women use FTS risk adjustment prior to determining if they want a diagnostic procedure (i.e. amniocentesis or chorionic villi sampling), as these diagnostic tests have ~0.5-1 % risk of pregnancy loss.

When can a woman have this test?

This test is available between the 11th and 14th weeks of the pregnancy.

How is the FTS obtained?

There are two parts to the test: a special ultrasound examination and a blood test. The ultrasound examination measures a thin layer of fluid found at the back of the baby’s neck, called the nuchal translucency (NT). A finger stick is used to collect a few drops of blood. Two biochemicals are measured in that blood sample: hCG (the pregnancy hormone) and PAPP-A (pregnancy associated plasma protein-A). These protein levels are evaluated, along with the NT measurement and the woman’s age, weight, race and the gestational age of the pregnancy, to provide an adjusted risk estimate.

What are Down syndrome and trisomy 18?

These chromosome abnormalities are caused by having an extra copy of either chromosome #21 (Down syndrome) or #18 (trisomy 18) in every cell of the developing baby. The extra chromosome contains many genes. This excess genetic material causes mental retardation and may also cause birth defects. The common forms of Down syndrome and trisomy 18 are usually not inherited and therefore may not be seen in families. The chance for any woman to have a baby with an extra chromosome increases with age.   

How accurate are the test results?

Because this is a screening test, a positive result does not mean that the baby has either Down syndrome or trisomy 18. This test detects 80-90% of pregnancies in which the baby has either condition. A nuchal translucency ultrasound can be performed without measuring the blood biochemicals; however, the detection rate for these two conditions is reduced to about 70%. First trimester screening is not designed to provide information about the risk of other chromosome conditions, nor about many other disorders, birth defects or causes of mental retardation. 

When will I get results? How are they reported?

Results are available in 3-4 days. They are reported as “positive” (risk higher than the cut-off) or “negative” (risk lower than the cut-off). The cut-off is equal to the risk of chromosome problems for a woman who is 35 years old. All results are expressed as a numerical ratio, e.g. 1/100 or 1/1000. This screening test never eliminates the possibility of having a baby with a chromosome abnormality. 

What if the results are positive?

A positive FTS does not mean that the baby has Down syndrome or trisomy 18. It means that there is an increased risk for this outcome. Genetic counseling will be available to discuss the test results and available options for further testing. 

What if the results are negative?

A negative screen means that the patient’s risks for Down syndrome and trisomy 18 are less than the screening cut-off. FTS can never eliminate the risk for Down syndrome or trisomy 18. Down syndrome and trisomy 18 make up about half of all sporadic chromosome abnormalities. FTS only estimates the risk for these two conditions; it does not screen for other possible chromosome abnormalities. As with any screening test, a negative result does not guarantee a healthy baby. 

Should a woman have the second trimester screening after having FTS?

The second trimester maternal serum screening test, also known as the ‘triple’ or ‘quad’ test, is performed between the 14-20 weeks of the pregnancy. Like the FTS, these tests statistically adjust a women’s age-related risk for Down syndrome and trisomy 18. In addition, the AFP portion of these screening tests can identify pregnancies at an increased risk for open neural tube defects such as spina bifida, which FTS does not screen for. While the 2nd trimester screening tests are certainly an additional screening option, it is unclear how to interpret results of the second test in light of the first. Currently, most laboratories do not combine results from the first and second trimester screening into one overall risk figure.

A detailed ultrasound is recommended in the second trimester for all FTS patients, in order to obtain a fetal anatomical survey. 

What if a patient will be over 35 years of age at delivery?

A woman's risk for having a baby with a chromosome abnormality gradually increases as she ages; however, all pregnant women should be informed about prenatal screening and diagnostic testing options. This recommendation was recently published by the American College of Obstetricians and Gynecologists (ACOG) in Practice Bulletin number 77 (January, 2007). 

What is the cost of this test?

The screening involves a charge for the ultrasound examination and the blood test. These charges may not be covered by insurance; a patient may want to check with her insurance company to see if her specific plan will cover these charges. The blood work will be performed by Genzyme laboratory and costs about $130.