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Nuchal scan

Nuchal scan - Wikipedia
Nuchal scan - Wikipedia

A nuchal scan or nuchal translucency (NT) scan/procedure is a sonographic prenatal screening scan (ultrasound) to detect chromosomal abnormalities in a fetus, though altered extracellular matrix composition and limited lymphatic drainage can also be detected. Since chromosomal abnormalities can result in impaired cardiovascular development, a nuchal translucency scan is used as a screening, rather than diagnostic, tool for conditions such as Down syndrome, Patau syndrome, Edwards Syndrome, and non-genetic body-stalk anomaly. There are two distinct measurements: the size of the nuchal translucency and the thickness of the nuchal fold. Nuchal translucency size is typically assessed at the end of the first trimester, between 11 weeks 3 days and 13 weeks 6 days of pregnancy. Nuchal fold thickness is measured towards the end of the second trimester. As nuchal translucency size increases, the chances of a chromosomal abnormality and mortality increase; 65% of the largest translucencies (>6.5mm) are due to chromosomal abnormality, while fatality is 19% at this size. A nuchal scan may also help confirm both the accuracy of the pregnancy dates and the fetal viability. All women, regardless their age, have a small chance of delivering a baby with a physical or cognitive disability. The nuchal scan helps physicians estimate the chance of the fetus having Down syndrome or other abnormalities more accurately than by maternal age alone. Down syndrome Overall, the most common chromosomal disorder is Down syndrome (trisomy 21). The likelihood rises with maternal age from 1 in 1400 pregnancies below age 25, to 1 in 350 at age 35, to 1 in 200 at age 40. Until recently, the only reliable ways to determine if the fetus has a chromosomal abnormality was to have an invasive test such as amniocentesis or chorionic villus sampling, but such tests carry a risk of causing a miscarriage estimated variously as ranging between 1% or 0.06%. Based on maternal age, some countries offer invasive testing to women over 35; others to the oldest 5% of pregnant women.

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Triple test
The triple test, also called triple screen, the Kettering test or the Bart's test, is an investigation performed during pregnancy in the second trimester to classify a patient as either high-risk or low-risk for chromosomal abnormalities (and neural tube defects). The term "multiple-marker screening test" is sometimes used instead. This term can encompass the "double test" and "quadruple test" (described below). The Triple screen measures serum levels of AFP, estriol, and beta-hCG, with a 70% sensitivity and 5% false-positive rate.
Chorionic villus sampling
Chorionic villus sampling (CVS), sometimes called "chorionic villous sampling" (as "villous" is the adjectival form of the word "villus"), is a form of prenatal diagnosis done to determine chromosomal or genetic disorders in the fetus. It entails sampling of the chorionic villus (placental tissue) and testing it for chromosomal abnormalities, usually with FISH or PCR. CVS usually takes place at 10–12 weeks' gestation, earlier than amniocentesis or percutaneous umbilical cord blood sampling.
Prenatal testing
Prenatal testing consists of prenatal screening and prenatal diagnosis, which are aspects of prenatal care that focus on detecting problems with the pregnancy as early as possible. These may be anatomic and physiologic problems with the health of the zygote, embryo, or fetus, either before gestation even starts (as in preimplantation genetic diagnosis) or as early in gestation as practicable.
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