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***The Maternal-Fetal Medicine Center of Northwest Arkansas is certified to perform fetal nuchal translucency screening


First trimester screen


First trimester screening is a screening test which shows if you are at an increased risk of having a baby with Down syndrome or Trisomy 18. It requires a sample of your blood and an ultrasound measurement of the nuchal translucency performed in early pregnancy.


Reasons for testing:

You may have many reasons for testing, including if you have:

  • concerns regarding Down syndrome and trisomy 18

  • a family history of Down syndrome or trisomy 18


Testing for first trimester screening screens for:

  • Down syndrome and trisomy 18.


What is Down syndrome?

Down syndrome is caused by the presence of an extra chromosome (#21) and results in both mental and physical abnormalities. Approximately 1 in 800 babies is born with Down syndrome. The risk of having a child with Down syndrome gradually increases with age of the mother, but can occur at any maternal age.


What is trisomy 18?

Trisomy 18 is caused by the presence of an extra chromosome (#18) and results in serious mental retardation and physical deformities, including major heart defects. Approximately 1 in 6500 babies is born with trisomy 18. Only 1 out of 10 babies affected with trisomy 18 lives past the first year of life. As with Down syndrome, the risk of having an affected child gradually increases with the age of the mother.


How the test works:

Between 10-13 weeks of your pregnancy, a small amount of your blood is drawn and the levels of a protein (PAPP-A) and a hormone (hCG) are measured.

These proteins and hormones are made by your body, the developing baby and the placenta, and are found in every pregnant woman’s blood. However, when a fetus is at risk for Down syndrome or trisomy 18, the amount of these proteins may be abnormal.

The results of a special ultrasound measurement, called nuchal translucency (NT), are combined with the blood test result to yield the final screening assessment.


What is a nuchal translucency?

Nuchal translucency (NT) is a measurement of the fluid filled space at the back of the developing fetus’ neck. Extra fluid in this space indicates that the fetus is at a higher risk for certain birth defects.


What's not detected?

First trimester screening does not test for open neural tube defects. A second trimester blood test called AFP or an ultrasound is required to detect open neural tube defects.

Every pregnancy has some risk (3-5%) for the kinds of birth defects that cannot be diagnosed during pregnancy, such as autism, non-specific mental retardation, some genetic diseases, and some types of physical birth defects.



Understanding your results:

A screening test does not provide a diagnosis; it predicts the likelihood of a problem to occur. First trimester screening tells you if there is an increased risk of your baby having Down syndrome or trisomy 18.


First trimester screening leads to the detection of approximately:

  • 83% of Down syndrome cases

  • 80% of trisomy 18 cases


The result “screen negative” means there is a low risk of your baby having Down syndrome or trisomy 18. However, in approximately 10% of pregnancies, these birth defects will not be detected through screening.

The result “screen positive” does not necessarily mean that your baby has one of these birth defects, but does mean that there is an increased risk for them. The next step is to talk with your doctor and/or genetic counselor about your results and your diagnostic testing options.


Some factors influencing your result:

  • exactly how far along you are in your pregnancy when the blood sample is taken and the ultrasound is performed

  • your weight, ethnic background and age

  • whether you are an insulin-dependent diabetic or take certain types of medications whether you have had a prior pregnancy or a close relative affected with Down syndrome or trisomy 18.



If a screening test is positive, it does not mean your baby has a birth defect. In fact, most women who have positive screening results have healthy babies.

Screening testing helps doctors to identify women who should be offered additional testing. Your doctor may recommend:

  • a more detailed ultrasound examination (which can often identify an open neural tube defect)

  • diagnostic testing, such as amniocentesis for chromosome abnormalities and open neural tube defects or chorionic villi sampling (CVS) for chromosome abnormalities.



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