Down Syndrome (Trisomy 21)

Down Syndrome, or Trisomy 21, is a congenital defect (mutation) caused by the presence of an extra chromosome 21 in all cells of the individual or fetus. Babies who are born with Down Syndrome have poor mental and physical development thus motor and social skills are delayed. The syndrome usually occurs in women over the age of 35 at a ratio of 1/365. As maternal age increases up to 45, the likelihood of the mother carrying a Down Syndrome fetus is 1/32. A Triple Screen test can be used to diagnose the baby with Down Syndrome, which measures three specific levels: AFP, hCG, and estriol. The invasive procedure is done through amnioscentesis or Chorionic Villus Sampling (CVS) in which amniotic fluid is drawn up from the mother to measure the levels of AFP, hCG, and estriol. If AFP levels are depressed, but hCG and estriol are elevated, there is an increased likelihood of a Down Syndrome fetus (however in Trisomy 18, all levels are depressed).

A specific marker for determining chromosomal abnormalities such as Down Syndrome is the Nuchal Translucency (NT) measurement. This measures the thickness in the back of the fetal neck during the 11-13 week scan. If the measurement is more than 3mm, then suspect Down Syndrome. Another marker that is associated with Down Syndrome is the Nuchal Fold (NF) measurement, which is measured in the back of the "fetal head". If the measurement is more than 6mm, then suspect a Down Syndrome fetus. Below is an image showing a normal NT measurement of 1.7mm in a late First Trimester fetus.



Other ultrasonic signs that are associated with Down Syndrome include the following:

Absence of nasal bone (from profile shot)
Cleft lip and palate (from facial shot)
Ventricularmegaly or Hydrocephalus (more than 10mm/1cm)
Low ear set
Cystic Hygroma
Cushion Defect (ASD)
VSD
Moderate Band (thick papillary muscle)
Esophageal Atresia (stenosis of gastroesophageal junction)
Duodenal Atresia (double bubble sign)
Echogenic Bowel
Hydronephrosis
Clinodactyly
Short femur and Humerus length (less than 0.91)
Sandal toe
Clubfoot

Below are videos explaining about Down Syndrome and its rise (listen up techs!)...