Ultrasound Detection of Down's Syndrome Delayed
By Barbara Lock, MDOctober 16, 2009
Researchers at the Technion-Israel Institute of Technology in Haifa, Israel, reported this week in the Journal of Clinical Ultrasound a series of cases of pregnant women who first trimester ultrasounds failed to detect so-called thickened nuchal soft tissues in their fetuses. Thickened nuchal soft tissues can be a marker for Down's Syndrome, also called Trisomy 21. The cases were all later detected on a second trimester ultrasound, and all were later determined to have trisomy 21.
Another ultrasound technique in which the fetus's developing humerus bone is measured, shows promise in the detection of Trisomy 21. Fetuses who have a very small humerus (less than 5th percentile), are much more likely to have Trisomy 21 than fetuses who have a larger humerus.
Trisomy 21 is a syndrome in which children are born with three copies of chromosome 21 in each cell instead of two. Children with trisomy 21 have impaired cognitive development, impaired motor development and frequently are born with heart defects. Some children with Trisomy 21 can live semi-independently as adults. The average lifespan is currently 49 years.
First trimester screening for Down's syndrome, when accurate, is far preferable to later screening, so that subsequent karyotyping can be performed to verify a genetic abnormality in time for a discussion with the parents about risks and benefits of carrying a Down's child to term. Karyotyping is done by amniocentesis, in which an obstetrician places a needle through the mother's abdominal wall and uterus to obtain amniotic fluid, which contain sloughed off fetal cells.
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