[Results of an experiment in systematic prenatal screening for neural tube malformations by assay of alpha fetoproteins in dried blood samples (12,480 pregnancies)]

Abstract

Measurement of alpha-fetoprotein (AFP) in eluate of dried blood was carried out in 12,480 pregnant women, between the 10th and 30th weeks of amenorrhea. In 348 cases, AFP level was greater than normal (greater than 99th centile). 225 control measurements were performed (123 women dropped out of the study). In 173 cases, the AFP level returned to normal (1.4% false positives). In 52 cases, AFP title remained above the 99th centile: in 8 cases, the fetus was malformed (4 anencephalics, 1 spina bifida, 1 hydrocephalus, 1 laparoschisis, 1 exomphalos). Of the 44 remaining cases, 26 were multiple pregnancies, 5 were cases of acute fetal distress, 7 false positives normalized when a second control was made, 5 false positives up to the end of pregnancy, and 1 spina bifida (normal ultrasound scan on two different occasions). During this prenatal screening, 7 false negatives (0.56%) not detected by AFP assay should be noted: 3 anencephalics, 2 spina bifida, 1 hydrocephalus, 1 exomphalos. In all cases except one, the AFP test was carried out too early (before the 10th week) or too late (after the 30th week). The authors stress that screening must be done during the precise period between the 16th and 20th weeks of amenorrhea, and that close collaboration with a competent ultrasonographist is necessary. In 5 cases of false negatives where AFP assay and ultrasound scan had been carried out, the two methods are compared. Measurement of AFP in eluate of dried blood thus seems a reliable test which could be the first stage in a plan for systematic prenatal screening for certain serious fetal malformations with high incidence (1,2% in the Midi-Pyrenees region).