How do doctors diagnose Down syndrome?
Three types of tests check for Down syndrome during a woman’s pregnancy: screening and diagnostic tests. Screening tests identify a mother who is likely carrying a baby with Down syndrome. The most common screening tests are the Triple Screen and the Alpha-Fetoprotein Plus. These tests measure levels of certain substances in the blood.
Alternatively, ultrasounds (which use sound waves to look inside the mother’s uterus) allow the doctor to examine the fetus in the womb for the physical signs of Down syndrome. To confirm a positive result identified in a screening test, one of the following diagnostic tests can be performed: chronic villus sampling (CVS), amniocentesis. Each takes a sample from the placenta, amniotic fluid, or umbilical cord, respectively, to examine the baby’s chromosomes and determine if he or she has an extra chromosome 21.
If Down syndrome is not diagnosed in the womb, doctors can usually recognize it after the baby is born by the distinctive facial features. The diagnosis is confirmed with a karyotype – an examination of the baby’s chromosomes.
Amniocentesis, chronic villus and ultrasound are the three primary procedures for diagnostic testing, which can identify certain abnormalities in the fetus.