Journal of Ultrasound in Medicine, Vol 4, Issue 6 307-310, Copyright © 1985 by American Institute of Ultrasound in Medicine
Sonography, a complementary examination to alpha-fetoprotein testing for fetal neural tube defects
B. E. Hashimoto, B. S. Mahony, R. A. Filly, M. S. Golbus, R. L. Anderson and P. W. Callen
Neural tube defects (NTDs) are among the most common congenital anomalies
in the United States, with an estimated prevalence of 16 per 10,000 births.
The measurement of amniotic fluid alpha-fetoprotein (AF-AFP) concentration
has been used to detect NTDs since the early 1970s. When the AF-AFP
concentration is elevated, ultrasonography is commonly used to confirm the
presence of a NTD. In this study, patient charts, amniocentesis records,
and ultrasound reports from a three-year period were reviewed. The 97
fetuses identified as being at high risk for NTDs were divided into four
groups: those with high AF-AFP concentrations (Groups 1 and 2, with from 3
to 5 standard deviations (SD) above the mean and with more than 5 SD above
the mean, respectively): those referred from other institutions because of
suspicious sonographic results (Group 3); and those at risk because of a
previous sibling with a NTD (Group 4). Ultrasonography was 100 per cent
sensitive and 100 per cent specific in diagnosing NTDs. Thus, in
pregnancies with an elevated AF-AFP concentration, ultrasonography can
reliably identify normal fetuses as well as differentiate between those
with NTDs and those with other congenital anomalies. Also, since AF-AFP
concentrations decline after 20 weeks' gestation, ultrasonography may be a
better test than a repeat amniocentesis in equivocal cases of AF-AFP
elevation.
