Prenatal Screening
Two types of prenatal tests are used to detect Down syndrome in a fetus:-
· screening tests and
· diagnostic tests.
Screening tests estimate the risk that a fetus has DS; diagnostic tests can tell whether the fetus actually has the condition.
Screening tests are cost-effective and easy to perform. But because they can't give a definitive answer as to whether a baby has DS, these tests are used to help parents decide whether to have more diagnostic tests.
Diagnostic tests are about 99% accurate in detecting Down syndrome and other chromosomal abnormalities. However, because they're performed inside the uterus, they are associated with a risk of miscarriage and other complications.
For this reason, invasive diagnostic testing previously was generally recommended only for women age 35 or older, those with a family history of genetic defects, or those who've had an abnormal result on a screening test. However, it is now recommended that all pregnant women be offered screening with the option for invasive diagnostic testing for Down syndrome, regardless of age.
If you're unsure about which test, if any, is right for you, your doctor or a genetic counselor can help you sort through the pros and cons of each.
Screening tests include:
Nuchal translucency testing. This test, performed between 11 and 14 weeks of pregnancy, uses ultrasound to measure the clear space in the folds of tissue behind a developing baby's neck. (Babies with DS and other chromosomal abnormalities tend to accumulate fluid there, making the space appear larger.) This measurement, taken together with the mother's age and the baby's gestational age, can be used to calculate the odds that the baby has DS. Nuchal translucency testing is usually performed along with a maternal blood test.
The triple screen or quadruple screen (also called the multiple marker test). These tests measure the quantities of normal substances in the mother's blood. As the names imply, triple screen tests for three markers; the quadruple screen includes one additional marker and is more accurate. These tests are typically offered between 15 and 18 weeks of pregnancy.
Integrated screen. This uses results from first-trimester screening tests (with or without nuchal translucency) and blood tests with a second trimester quadruple screen to come up with the most accurate screening results.
A genetic ultrasound. A detailed ultrasound is often performed at 18 to 20 weeks in conjunction with the blood tests, and it checks the fetus for some of the physical traits abnormalities associated with Down syndrome. [3]
· screening tests and
· diagnostic tests.
Screening tests estimate the risk that a fetus has DS; diagnostic tests can tell whether the fetus actually has the condition.
Screening tests are cost-effective and easy to perform. But because they can't give a definitive answer as to whether a baby has DS, these tests are used to help parents decide whether to have more diagnostic tests.
Diagnostic tests are about 99% accurate in detecting Down syndrome and other chromosomal abnormalities. However, because they're performed inside the uterus, they are associated with a risk of miscarriage and other complications.
For this reason, invasive diagnostic testing previously was generally recommended only for women age 35 or older, those with a family history of genetic defects, or those who've had an abnormal result on a screening test. However, it is now recommended that all pregnant women be offered screening with the option for invasive diagnostic testing for Down syndrome, regardless of age.
If you're unsure about which test, if any, is right for you, your doctor or a genetic counselor can help you sort through the pros and cons of each.
Screening tests include:
Nuchal translucency testing. This test, performed between 11 and 14 weeks of pregnancy, uses ultrasound to measure the clear space in the folds of tissue behind a developing baby's neck. (Babies with DS and other chromosomal abnormalities tend to accumulate fluid there, making the space appear larger.) This measurement, taken together with the mother's age and the baby's gestational age, can be used to calculate the odds that the baby has DS. Nuchal translucency testing is usually performed along with a maternal blood test.
The triple screen or quadruple screen (also called the multiple marker test). These tests measure the quantities of normal substances in the mother's blood. As the names imply, triple screen tests for three markers; the quadruple screen includes one additional marker and is more accurate. These tests are typically offered between 15 and 18 weeks of pregnancy.
Integrated screen. This uses results from first-trimester screening tests (with or without nuchal translucency) and blood tests with a second trimester quadruple screen to come up with the most accurate screening results.
A genetic ultrasound. A detailed ultrasound is often performed at 18 to 20 weeks in conjunction with the blood tests, and it checks the fetus for some of the physical traits abnormalities associated with Down syndrome. [3]