This prenatal test (also called the NT or nuchal fold scan) can help us assess your baby's risk of having Down syndrome and some other chromosomal abnormalities, as well as major congenital heart problems.
The NT test uses ultrasound to measure the clear (translucent) space in the tissue at the back of your developing baby's neck. Babies with abnormalities tend to accumulate more fluid at the back of their neck during the first trimester, causing this clear space to be larger than average. At the same time that this measurement is made, we obtain a drop of the mother's blood to measure the levels of pregnancy-related proteins. These measurements are used together to tell us how likely the baby is to have one of these disorders.
Like other screening tests, an NT scan won't give you a final diagnosis, but it can assess your baby's risk for certain problems. If the risk is low, you will be reassured to know that your baby is unlikely to have these chromosomal problems. However, if the risk is high, it does not mean that the baby is definitely affected. In the case of a "positive" test, we will refer you for genetic counseling, and you can decide whether you would like to proceed with more definitive testing, in the form of chorionic villus sampling (CVS) or amnioctesis (your options depend on your gestational age).
The NT scan must be done when you're between 11 and 14 weeks pregnant. First-trimester screening lets you learn about your baby's risk for chromosomal problems relatively early in the pregnancy without subjecting yourself to the slight risk of miscarriage from an invasive test like CVS or amniocentesis. First-trimester screening does not diagnose all problems, so even with a normal NT, you will still be offered testing later in the pregnancy for other problems, such as neural tube defects, as well as a routine ultrasound for assessment of your baby's development during the second trimester.