Today Down syndrome screening is a routine aspect of prenatal care. As recommended by the American Congress of Obstetricians and Gynecologists, all pregnant women have the opportunity to undergo various forms of Down syndrome testing, regardless of their age or family history. These tests are typically undergone during the first and second trimester.
Common Forms of Screening:
Currently, women are more likely to choose the first trimester combined test including both an ultrasound and blood testing. These tests are carried out during weeks 11 to 13 of the pregnancy. Through the ultrasound, doctors examine a specific area on the back of the fetus’ neck. Abnormalities are likely to be shown in this region by the collection of an unusual amount of fluid. The blood tests look for abnormal levels of the mother’s pregnancy associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (HCG).
Another option for Down syndrome screening is a two part, full integrated test. The first part is done in the first trimester and includes the previously discussed ultrasound and blood testing. Part two is a measurement of four pregnancy-linked substances that is completed in the second trimester. A squad screen is used to measure the blood levels of alpha fetoprotein, inhibin A, estriol, and HCG.
The ultrasound below shows the the abnormal fluid build up that may occur on the backside a baby's neck. This is a possible sign of Down syndrome.
When pregnancy screenings result in a high risk of having a Down syndrome baby, many women undergo further testing. Three common diagnostics tests for this purpose are Amniocentesis, Chronic villus sampling, and percutaneous umbilical blood samplings.
CVS or chronic villus sampling is usually carried out between weeks 9 and 14 of gestation. Cells are extracted from the mother’s uterus and examined for abnormalities in the fetal chromosomes. The risk of miscarriage is 1 in 100.
Amniocentesis is when the fluid around the fetus is used to analyze its chromosomes. Doctors perform Amniocentesis by placing a hollow needle into the mother’s uterus to retrieve a sample of amniotic fluid. There is a 1 in 200 risk of miscarriage in this form of Down syndrome testing.
Percutaneious umbilical blood samplings, also known as PUBS, is the sampling of blood from an umbilical cord vein that is also used to examine the chromosomes of the baby. This test carries the highest risk of miscarriage and is typically done during the 18th week of pregnancy.