Trisomy 21
Introduction
Down syndrome or trisomy 21 is caused by nondisjunction of chromosome 21 in a parent who is chromosomally normal and is one of the most common chromosomal abnormalities in liveborn children. The frequency of trisomy 21 in the population is approximately 1 in 650 to 1,000 live births, in Australia between 1991-97 there were 2,358 Trisomy 21 (Down) infants.
Recent attention has focussed on screening for Down's syndrome (mainly in terms of cost and efficiency) during fetal life with over 350 articles in the medical literature in just the past five years. There is also a high correlation of increased occurance with an increase in maternal age.
American College of Obstetricians and Gynecologists Recommendations
The following ACOG recommendations (January 2007) are based on good and consistent scientific evidence:
- First-trimester screening using both nuchal translucency (NT), an ultrasound exam that measures the thickness at the back of the neck of the fetus, and a blood test is an effective screening test in the general population and is more effective than NT alone.
- Women found to be at increased risk of having a baby with Down syndrome with first-trimester screening should be offered genetic counseling and the option of CVS or mid-trimester amniocentesis.
- Specific training, standardization, use of appropriate ultrasound equipment, and ongoing quality assessment are important to achieve optimal NT measurement for Down syndrome risk assessment, and this procedure should be limited to centers and individuals meeting this criteria.
- Neural tube defect screening should be offered in the mid-trimester to women who elect only first-trimester screening for Down syndrome.
Text extract from: New Recommendations for Down Syndrome Call for Screening of All Pregnant Women (press release January 2, 2007)
