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False-positive acetylcholinesterase with early amniocentesis
B K Burton1, L H Nelson, M J Pettenati
1Department of Pediatrics and Obstetrics, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina.
Obstetrics and Gynecology
|October 1, 1989
Summary
Early amniocentesis acetylcholinesterase tests show unexplained false positives. Repeat testing and careful interpretation are crucial for accurate neural tube defect screening in early pregnancy.
Area of Science:
- Prenatal Diagnostics
- Biochemistry
- Obstetrics
Background:
- Acetylcholinesterase (AChE) testing in amniotic fluid is a standard method for detecting fetal neural tube defects (NTDs).
- Early second-trimester screening (11-14 weeks' gestation) is becoming more common, necessitating evaluation of test reliability at this gestational age.
Purpose of the Study:
- To assess the reliability of acetylcholinesterase (AChE) testing in amniotic fluid for detecting fetal neural tube defects (NTDs) in early pregnancies (11-14 weeks' gestation).
- To evaluate the utility of the AChE-to-pseudocholinesterase (PChE) ratio in early gestation screening.
- To determine the significance of false-positive AChE results in early amniotic fluid samples.
Main Methods:
- Analysis of 93 amniotic fluid samples for AChE from pregnancies at 11-14 weeks' gestation.
- Comparison of AChE results with those from 951 samples at 15-20 weeks' gestation.
- Performance of repeat amniocentesis in cases with initially positive AChE results.
Main Results:
- Five unexplained false-positive AChE results were observed in the early gestation group (11-14 weeks).
- In four false-positive cases, the AChE/PChE ratio mimicked that seen with NTDs, but repeat amniocentesis yielded negative results, and all pregnancies had normal outcomes.
- No false-positive results were found in the later gestation group (15-20 weeks).
- The AChE/PChE ratio was not a reliable indicator for NTDs before 15 weeks' gestation.
Conclusions:
- Positive AChE results from early amniocentesis (11-14 weeks) should be interpreted with caution, particularly if amniotic fluid alpha-fetoprotein levels are not significantly elevated.
- The AChE/PChE ratio is not useful for identifying fetal NTDs before 15 weeks' gestation.
- Repeat amniocentesis can help clarify the significance of a positive AChE result in early gestation when ultrasonography reveals no fetal abnormalities.