Genetic Testing
WHAT IS A NUCHAL TRANSLUCENCY MEASUREMENT?
A nuchal translucency (NT) measurement uses ultrasound to measure the fluid underneath the skin at the back of your baby's neck. All babies have some fluid; but too much fluid, resulting in an increased NT measurement, is associated with an increased risk for a chromosome abnormality, whereas a normal measurement suggests a lower risk. An increased NT measurement also can be associated with other genetic conditions and certain birth defects, including heart anomalies. This testing ONLY can be completed between 11 and 13 weeks. This screening involves no risk to your baby and is typically done in combination with a blood test as the first part of the sequential screen (see below). An NT measurement can give us early information about whether you need more testing. It is important to note that this screening will not give you a definitive diagnosis. If your baby is found to be at increased risk, you likely will be referred to a genetic counselor and will be offered additional testing, such as chorionic villus sampling (CVS), amniocentesis, level II ultrasound, or a fetal echocardiogram. Some of these tests are more invasive and may involve risks to you or your baby. A genetic counselor can explain the risks and benefits to these testing options, but the decision to pursue additional testing would be yours.
WHAT IS THE DIFFERENCE BETWEEN A QUAD SCREEN AND A SEQUENTIAL SCREEN?
Both of these tests can be used to screen for Down syndrome, Trisomy 18 (a less common but more severe chromosome abnormality), and open neural tube defects (an opening in a baby's head or spinal column) during pregnancy. A sequential screen is a two-part screen comprised of an NT measurement and a blood draw between 11 and 13 weeks combined with a second trimester quad screen drawn between 15 and 21 weeks. It is the combination of the NT measurement and the blood work that provides us with information regarding the chance for your baby to have any of these conditions. If a patient does not have an NT measurement or the blood draw between 11 and 13 weeks, she can still have blood drawn for a quad screen between 15 and 21 weeks, though the detection rate is slightly lower and the false positive rate slightly higher when the quad screen is done alone. Your healthcare provider or a genetic counselor can discuss these testing options in more detail. It is important to note that neither of these tests will give you a definite diagnosis. If your baby is found to be at increased risk, you will likely be referred to a genetic counselor and will be offered additional testing, such as CVS, amniocentesis, or a level II ultrasound. Again, the decision to pursue these additional tests would be yours.
ARE THERE ANY OTHER GENETIC TESTS I SHOULD CONSIDER?
Other genetic testing may be offered to an individual patient based on their ethnic background as well as their personal and family histories. If you are a candidate for additional genetic testing, your healthcare provider will either discuss it with you or refer you to a genetic counselor for more information. Once more, the decision to pursue any of this genetic testing would be yours.
