The blood test given during the first trimester screening is for chromosomal abnormalities in the baby, including Down's Syndrome (trisomy 21), Edwards Syndrome (trisomy 18), skeletal defects, or heart defects.
Partial trisomy of the proximal segment of chromosome 13 is much less likely to be fatal and has been associated with a variety of facial features including a large nose, a short upper lip, and a receding jaw.
Called nuchal translucency, the measurement tends to be larger in fetuses with genetic abnormalities such as Down syndrome, trisomy 13, trisomy 18, Turner syndrome, and triploidy.
Approximately 45 percent of trisomy 13 babies die within their first month of life; up to 70 percent in the first six months; and over 70 percent by one year of age.
Down syndrome is a condition that includes mental retardation and a distinctive physical appearance linked to an abnormality of chromosome 21 (called trisomy 21).