Abstract

Pregnancies at risk of being associated with (open) neural tube defects can be identified by maternal serum and amniotic-fluid alphafetoprotein (AFP) concentrations in excess of established screening cut-off valves in conjunction with the results of an amniotic fluid electrophoretic acetylcholinesterase screening test. The risk associated with the AFP cut-off values are formulated in terms of a population screening programme. These "population risks" are of little value in the assessment of test results from individual "at-risk" pregnancies, especially when the observed AFP concentrations are in proximity to the "cut-off" values. A complete risk assessment procedure for individual pregnancies is described and presented in graphical form to permit immediate access by clinical staff.