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First Trimester Tests And Screenings

First trimester screening is a combination of fetal ultrasound and maternal blood testing performed during the first trimester of pregnancy. This screening process can help determine the risk of the fetus having certain birth defects. Screening tests may be used alone or in combination with other tests.

There are three parts of first trimester screening:

  • Ultrasound test for fetal nuchal translucency (NT)Nuchal translucency screening uses an ultrasound test to examine the area at the back of the fetal neck for increased fluid or thickening.
  • Two maternal serum (blood) testsThese blood tests measure two substances found in the blood of all pregnant women: 
    • Pregnancy-associated plasma protein screening (PAPP-A), which is a protein produced by the placenta in early pregnancy. Abnormal levels are associated with an increased risk for chromosome abnormality.
    • Human chorionic gonadotropin (hCG),which is is a hormone produced by the placenta in early pregnancy. Abnormal levels are associated with an increased risk for chromosome abnormality.

When used together as first trimester screening tests, nuchal translucency screening and maternal blood tests have a greater ability to determine if the fetus might have a birth defect, such as Down syndrome (trisomy 21) and trisomy 18.

If the results of these first trimester screening tests are abnormal, genetic counseling is recommended. Additional testing, such as chorionic villus samplingamniocentesis, cell-free fetal DNA or other ultrasounds, may be needed for accurate diagnosis.

How is first trimester screening performed?

First trimester screening generally involves the following tests, which are performed between the 10th and 14th weeks of pregnancy:

  • An ultrasound test, usually a transvaginal ultrasound, will help your health care provider examine the fetus. During a transvaginal ultrasound, a small ultrasound transducer is inserted through the vagina to visualize the fetus.
  • A blood test that will be sent to the laboratory for analysis.

First trimester screening is not 100 percent accurate. It is only a screening test to determine if there is an increased risk of the fetus having a birth defect. It also helps identity those women who may need additional testing or monitoring during their pregnancy. There can be false-positive results, which indicate a problem when the fetus is actually healthy, or false-negative results, which indicate a normal result when the fetus actually does have a health problem.