A reappraisal of amniotic fluid alpha-fetoprotein measurement at the time of genetic amniocentesis and midtrimester ultrasonography.

Abstract

To evaluate the contemporary utility of amniotic fluid alpha-fetoprotein measurement as a complementary test for fetal abnormalities at the time of invasive genetic testing. A review of amniotic fluid alpha-fetoprotein test results was conducted to determine the frequency with which elevated alpha-fetoprotein values added independent diagnostic information and altered clinical management. Amniotic fluid specimens processed for alpha-fetoprotein between 1995 and 1998 were included. Elevated alpha-fetoprotein cases were classified as either incidental to the fetal abnormality diagnosed or central to the identification of a fetal anomaly on the basis of whether an ultrasonographic examination had already identified the anomaly before amniocentesis. The costs associated with alpha-fetoprotein testing were used to estimate the expenditure per pregnancy in which elevated alpha-fetoprotein values would add discriminatory diagnostic value. A hypothetical national cost model was constructed to explore the utility of selective rather than routine amniotic fluid alpha-fetoprotein measurement. Eighty-two (3%) of 2769 amniotic fluid alpha-fetoprotein values were elevated. In only 1 instance was the elevated result found to be partially discriminatory (e.g., an established diagnosis of microcephaly with an associated small encephalocele identified after the elevated amniotic fluid alpha-fetoprotein value prompted repeated ultrasonographic assessment). Sixty-one other neural tube defects were detected by ultrasonography alone (myelomeningocele, n = 28; anencephaly, n = 24; and encephalocele, n = 9). Thus, an elevated alpha-fetoprotein result added diagnostic precision in only 1 (0.036%) of 2769 cases. Cost estimates suggested that routine amniotic fluid alpha-fetoprotein assessment resulted in a $219,000 expenditure per informative case. Routine measurement of amniotic fluid alpha-fetoprotein during amniocentesis may not be warranted in centers with expertise in targeted ultrasonographic imaging.