Are routine alpha-fetoprotein and acetylcholinesterase determinations still necessary at second-trimester amniocentesis? Impact of high-resolution ultrasonography.

OBJECTIVE: To audit routine measurement of alpha-fetoprotein (AFP) and acetylcholinesterase in amniotic fluid (AF) samples obtained at second-trimester amniocentesis.
METHODS: We reviewed retrospectively 1737 consecutive AF specimens obtained for cytogenetic evaluation over a 4-year period and routinely assayed for AFP and acetylcholinesterase. In all instances, high-resolution ultrasonography was performed before amniocentesis. Details of pregnancy outcome of all cases with AF AFP levels greater than 2.0 multiples of the median and a positive or faint acetylcholinesterase band were obtained.
RESULTS: There were 31 abnormal results (1.8%, 1 of 56). Of these, 25 cases had elevated AF AFP and/or positive acetylcholinesterase. Ultrasonography correctly identified all 18 fetuses with anomalies associated with abnormal levels of these biochemical markers, including open neural tube defects and/or anterior abdominal wall defects (17 cases) and fetal hydrops (one). In the remaining seven, no fetal anomalies were detected, and all neonates were structurally normal after birth. In addition, six pregnancies with faint acetylcholinesterase and normal AF AFP showed no fetal abnormalities at ultrasonographic examination and post-delivery.
CONCLUSIONS: High-resolution ultrasonography was more accurate than AF biochemistry in the detection of congenital anomalies associated with elevated AFP levels and acetylcholinesterase in the AF. Routine measurement of these biochemical markers in AF samples obtained for cytogenetic analysis appears to have a very low yield and would therefore not be cost-effective in practices where high-resolution ultrasonography is performed before amniocentesis.