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First Trimester Screening

What is first trimester screening?

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 to determine the risk of the fetus having certain birth defects.

There are three parts of first trimester screening:

Illustration of transabdominal fetal ultrasound

When used together, nuchal translucency screening and the maternal blood tests have a greater ability to determine if the fetus might have a birth defect, such as Down syndrome, trisomy 18, or trisomy 13.

If first trimester screening is abnormal, additional testing such as chorionic villus sampling, amniocentesis, or other ultrasound procedures may be necessary for accurate diagnosis.

How is first trimester screening performed?

Although the specific details of each procedure vary slightly, first trimester screening generally involves the following tests to be performed between the 10th and 14th weeks of pregnancy:

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 to identity those women who may need additional testing or monitoring during their pregnancy. There can be false-positive results - indicating a problem when the fetus is actually healthy, or false negative results - indicating a normal result when the fetus actually does have a health problem.

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