These screening methods are less accurate and are performed between 15-20 weeks.
It is very important to remember what a screening test is before getting one performed.This will help alleviate some of the anxiety that can accompany test results.Screening tests do not look only at results from the blood test.The First Trimester Screen is a new, optional non-invasive evaluation that combines a maternal blood screening test with an ultrasound evaluation of the fetus to identify risk for specific chromosomal abnormalities, including Down Syndrome Trisomy-21 and Trisomy-18.In addition to screening for these abnormalities, a portion of the test (known as the nuchal translucency) can assist in identifying other significant fetal abnormalities, such as cardiac disorders.
The screening test does not detect neural tube defects.
The first trimester screen has been available in the U. for several years, but has only recently been determined an effective means of early chromosomal abnormality screening.
A study published in the New England Journal of Medicine in November 2005 determined that first trimester screening was the most accurate non-invasive screening method available.
The combined accuracy rate for the screen to detect the chromosomal abnormalities mentioned above is approximately 85% with a false positive rate of 5%.
This means that: It is important to realize a positive result does not equate to having an abnormality, but rather serves as a prompt to discuss further testing.
The screen should not be confused with screens performed during the second trimester (often known as the Quad Screen or Triple Screen ).