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New blood test improves antenatal screening for Down's syndrome.

The definitive antenatal screening tests for Down's syndrome are amniocentesis or chorionic villus sampling (CVS). However, as these procedures may in a small number of cases cause spontaneous abortion, it is important that they are only used when the risk of abnormalities in the fetus is high. A number of indicators can be used in assessing that risk; maternal age is a key determinant along with ultrasound, fetal biometric measurements and three maternal serum factors--alphafetoprotein (AFP), human chorionic gonadotropin (HCG) and unconjugated oestriol (uE3). The relative value of each of these as predictors may vary according to the timing of the test, but in general the more combinations used, the better the chance of detecting true abnormalities and reducing false positives. So, for example, if using maternal age alone is compared with using maternal age plus AFP/ HCG/uE3, the detection rate increases from about 49% to 78% and the false-positive rate drops from about 13% to 8%. Now, two recent studies suggest that a fourth serum measurement, inhibin-A, should be added to second-trimester tests, increasing the detection rate to about 81% and decreasing the false positive rate to 7%. It is therefore becoming policy not to use maternal age alone as a sufficient basis for offering amniocentesis of CVS. Incorporation of serum and ultrasound screening is becoming routine practice instead. (1-3)

(1.) Benn P. Improved antenatal screening for Down's syndrome [Commentary]. Lancet: 2003;361(9360):794.

(2.) Benn PA, Fang M, Egan JF, et al. Incorporation of inhibin-A in second-trimester screening for Down syndrome. Obstetrics and Gynecology 2003;101(3): 451-54.

(3.) Wald NJ, Huttly WJ, Hackshaw AK. Antenatal screening for Down's syndrome with the quadruple test. Lancet 2003;361(9360):835-36.
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Title Annotation:Research
Publication:Reproductive Health Matters
Date:Nov 1, 2003
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