Screening for neural tube defect with maternal serum a-fetoprotein and ultrasound without the use of amniocentesis

A population screening programme for neural tube defects, consisting of maternal serum αfetoprotein estimations combined with ultrasound scanning but avoiding the use of amniocentesis, was evaluated. In 23 369 pregnancies screened by ultrasound in the early part of the second trimester, 76 fetuses were affected by a neural tube defect. Of these 70 were correctly predicted while six were missed. Three of these six defects missed by ultrasound scan were associated with elevated maternal serum αfetoprotein levels. The sensitivity of the programme was 92-1 per cent, and the specificity and predictive value of a positive test 100% since there were no false positive diagnoses. Of 620 women with an elevated level of αfetoprotein, 7-5 per cent had fetuses affected by neural tube defects or related abnormalities, while 47-4 per cent had no identifiable cause. As a marker for abnormality serum αfetoprotein estimation was useful, in these women the use of high resolution ultrasound reduced the need for amniocentesis, avoiding the problems associated with that procedure.