Neural-tube defect risk assessment for individual pregnancies using alphafetoprotein and acetylcholinesterase test results.

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.