Alpha-Fetoprotein Screening in Obstetric Practice and the Use of Differential Action Limits

The efficiency of a general AFP-screening program is considerably affected by the action limit used for recommended diagnostic follow-up procedures.We have analyzed if this efficiency could be enforced by the use of differential action limits for different purposes.A total of 18 037 pregnancies of known outcome were analyzed for their AFP-levels in maternal serum (MS-AFP) between the 15th and 17th gestational weeks. The individual AFP test results were expressed in multiples of the normal median value (MOM) for singleton pregnancies of the same gestational age. MS-AFP levels ≤ 3 MOM were found in 22/28 pregnancies (78.6 per cent) affected by open neural tube- or abdominal wall defects, but only in 0.7 per cent of the 17 872 normal singleton pregnancies.Obstetric risk pregnancies, e.g. multiple pregnancies, impending abortions, and pregnancies eventually ending with perinatal deaths and children with low birth weight, were found to be overrepresented above the MS-AFP level 1.8 MOM (the 94th percentile). Th...