The American College of Obstetricians and Gynecologists recommend that all pregnant women be tested for Down syndrome during the first-trimester.
Screening for Down syndrome is offered as a part of prenatal care. Traditionally, a mother’s age often was the determining factor when recommending a Down syndrome screen. But now, the American College of Obstetricians and Gynecologists recommends offering less invasive screening tests for Down syndrome to all pregnant women, regardless of age.
Down syndrome screening tests will assess the likeliness of a mother to carry a baby with Down syndrome. It will not confirm or give a diagnosis of Down syndrome; it will only assess a mother’s risk of carrying a baby with a genetic disorder such as Down syndrome. If the screening results show the mother to be at increased risk of having a child with Down syndrome, then more invasive diagnostic tools such as chorionic villus sampling or an amniocentesis may be offered along with genetic counseling.
There are currently two tools recommended to screen for Down syndrome: the triple screen (alpha-fetoprotein plus) and an ultrasound. Both screening tools are noninvasive and have no side effects or risk to the baby. The American College of Obstetricians and Gynecologists recommend that these two tools be used together between the 11th and 14th week of pregnancy. When these screening processes are done during the 11th week of pregnancy, researchers say it can identify 87 percent of babies with Down syndrome. The accuracy declines between the 12th and 14th week of pregnancy.
Triple Screen (alpha-fetoprotein plus) Screening
The triple screen, also known as the alpha-fetoprotein plus or the marker screening, is a blood screening test that looks at three substances: alpha-fetoprotein, human chorionic gonadotropin and estriol. The alpha-fetoprotein (AFP) is a protein that is manufactured by the fetus, human chorionic gonadotropin is a hormone manufactured by the placenta and estriol is an estrogen manufactured by the placenta and the fetus. The triple screen will measure high and low levels of AFP and measure abnormal levels of HCG and estriol. The results are combined with a variety of other factors including the mother’s age, weight, ethnicity and gestational age of the fetus to assess the possibility of the risk of Down syndrome or other complications.
Ultrasound Screening
Nuchal transluceny screening is used in combination with the blood tests to assess the mother for possible risks of carrying a child with Down syndrome. Ultrasounds are used to perform the nuchal transluceny screening test. This prenatal test measures space in the tissue at the back of the developing baby’s neck. Babies with abnormalities often accumulate more fluid in the back of their neck during the first-trimester, causing a larger than average space. The ultrasound measures the space behind the neck and then the measurements can be printed out for the patient or physician.
After both screening tools have been used, the risk of carrying a Down syndrome child will be assessed. If the risk is high, the physician may recommend diagnostic testing such as chorionic villus sampling (CVS), amniocentesis or percutaneous umbilical blood sampling (PUBS).
