Nuchal Translucency Screening (First Trimester Screening)

Dr. Lescale offers first trimester screening, a revolutionary new non-invasive screening test that combines a blood test with a nuchal translucency measurement to help determine with greater accuracy whether a fetus may have Down syndrome, Trisomy 18, or other chromosome abnormalities. It can also detect congenital heart defects. Traditionally women at high-risk for problems due to maternal age or family history have been offered chorionic villus sampling (CVS) in their first trimester, or waited until the second trimester to have an amniocentesis, both of which carry their own risks. First trimester screening allows patients to push their decision making up a month, and provides reassurance of a healthy pregnancy earlier than any other test permits.

Ultrasound ImageThis test has been performed in the United States since 1995, but is still not widely available. To perform the procedure the physician needs high quality equipment and must be certified by the Fetal Medicine Foundation in London, the organization that currently set the standards and provides the software that allows the doctor to evaluate risk.

By using ultrasound the doctor measures the clear space at the back of the baby's neck. The measurement of this fluid is called a nuchal translucency measurement. Babies with abnormalities tend to accumulate more fluid at the back of their necks during the first trimester, causing a larger nuchal translucency measurement. The test is painless and involves no risk to the patient or fetus. The Screening must be performed between 11 and 14 weeks. In the first stage of the test the baby’s gestational age will be confirmed. Next a probe is placed over the abdomen so that the nuchal fold area shows up on the monitor. The thickness of the nuchal fold area is measured with calipers.

By evaluating the measurements of nuchal folds of thousands of fetuses between 11 and 14 weeks of gestation, researchers have been able to establish what a “normal” measurement is for each day of the three weeks studied. Then a statistical relationship is created between the nuchal fold measurement, the fetus’ age, the mother’s age, and the probability that the baby will be born with certain abnormalities. The doctor gives the patient the result in the form of a ratio that expresses the baby’s chances for having a problem. For example a forty-year-old pregnant woman has a 1 in 77 chance of having a baby with Down syndrome. After she has a nuchal translucency test the doctor find the baby’s nuchal fold to be thin for his age. The doctor enters the mother’s age, the nuchal fold measurement, and the fetus’ age in the risk assessment program. The result reveals that the baby’s risk for having Down syndrome is now 1 in 761.

For the second part of the test a blood specimen is taken from the mother by a simple finger prick. The blood is then analyzed for two proteins, freeBeta-hCG and PAPP-A, normally found in the blood of all pregnant women. By combining the nuchal translucency results and blood analysis, the doctor can detect approximately ninety-percent of babies with Down syndrome and Trisomy 18. It is important to remember that the screening does not give a definite diagnosis, but the results can aid the patient in deciding whether or not to undergo more invasive diagnostic tests like CVS or amniocentesis.

 

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© 2018 Keith Lescale, M.D., F.A.C.O.G.