Maternal serum screening for trisomy 21 in women with a false positive result in last pregnancy

Abstract

Maternal serum screening for Down syndrome is a common practice in the United Kingdom. A number of factors have been shown to influence the chance of a false positive test result. Analysis of routinely collated information stored on an electronic database in a district general hospital has shown that women with a previous false positive maternal screen are at much greater chance of having a false positive result in their next pregnancy. Overall, there was a fivefold increased risk attributed to biological variation in their serum concentrations of alpha-feto protein (AFP) and human chorionic gonadotrophin (hCG). The potential effect of this was to increase the chance of such women having an unnecessary amniocentesis. Women should be advised of this effect in subsequent pregnancies. Ideally a correction factor should be applied which would reduce the false positive rate without affecting adversely the sensitivity of the test.