Combined First-Trimester Screening
A variety of prenatal tests are offered to women throughout the varying stages of pregnancy in order to ensure the health of their babies. These tests are designed to identify a child’s risk of developing birth defects, like Tay-Sachs disease and Downs syndrome. While every woman wants to ensure the health of her child, some of these prenatal screening tests can increase the risk of a miscarriage. Additionally, they are often not performed until the second trimester and tend to carry a high rate of false positives. However, recently a new test has been developed that is not only risk-free, but is performed in the first trimester and more accurate.
Known as the combined first-trimester screening test (CFTS), this new test involves using a sample of maternal blood as well as ultrasound images to assess a fetus’ risk of Downs syndrome and trisomy 18.
In CFTS, a sample of blood from the mother is removed through a simple pin-prick. This tiny sample is then assessed for free beta hCG and a protein called pregnancy-associated plasma protein (PAPP-A). Abnormal hormone and protein levels indicate a higher risk of the child developing Downs syndrome. Additionally, special ultrasound or sonogram images are taken of the fetus and then examined to measure the skin thickness at the back of the baby’s neck (the nuchal translucency). In this case, an abnormal measurement can indicate a risk of trisomy 18.
Advantages of CFTS
While all prenatal testing is beneficial and an important part of proper prenatal care, often women are reluctant to take advantage of these tests and for good reason. Chorionic villus sampling (CVS), the only type of prenatal screening available in the first trimester until recently, and amniocentesis both carry a risk of miscarriage with them. Prenatal blood tests, like the triple and quadruple screening tests, are considered to be safe but they do have a fairly high rate of false positives associated with them. Thankfully, CFTS does not have any of these disadvantages.
Combined first-trimester screening can be performed as early as 10-and-a-half to 11 weeks into a pregnanacy. There is no risk to the fetus, as ultrasound images are used, or to the mother, as only a pin prick of blood is required. Additionally, in a recently released major US study involving 38,167 women, CFTS was found to be 87% accurate in detecting Downs syndrome, compared to the 81% accuracy rate associated with the quadruple test. Combining the two types of prenatal genetic testing was found to be 95% accurate, carrying a false positive rate of only 5%. However, neither of these tests are considered to be prenatal diagnostic tests. Therefore, it would still be necessary to have an amniocentesis or CVS done to confirm the results.
Because CFTS is performed so early on in pregnancy, women have many more options as to how they would like to proceed in their pregnancy. Consideration of pursuing more invasive testing can be done so earlier. Parents who decide they would like to terminate their pregnancy may do so at an earlier stage when the procedure is safer.
The early testing time frame of CFTS also means that couples have more time to emotionally prepare themselves for raising a child with Downs syndrome while those that have had a test come back clear of any increased risks can have their anxiety relieved sooner.
CFTS has only just started to become available. Not all prenatal health care professionals are trained or set up to do this type of test. However, with CFTSs now proven high accuracy rate and safety, it is only a matter of time before it becomes a standard test offered to every pregnant woman.
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