[Alpha-foetoprotein assessment in amniotic fluid for the detection of neural tube defects: limited added value beyond week 20 ultrasound; retrospective study].

OBJECTIVE: To evaluate the diagnostic additional value of routine alpha-foetoprotein (AFP) assessment in amniotic fluid for the detection of neural tube defects (NTDs), compared with week 20 ultrasonographic examination. DESIGN: Retrospective. METHOD: We retrospectively determined AFP concentrations in amniotic fluid obtained from 7981 women who had undergone amniocentesis for karyotyping and AFP assessment. An AFP concentration greater than 2.5 times the median was considered abnormal. Women were categorised into 4 groups based on the indication for invasive prenatal diagnostic assessment: advanced maternal age (group I; n = 6179), increased risk of foetal NTDs (group II; n = 258), ultrasonographically confirmed foetal NTDs (group III; n = 55) or other indications (group IV; n = 1489). RESULTS: In group I, 18 of 6179 samples had increased AFP levels (0.3%), 2 of which were associated with NTDs. In group II, 2 of 258 samples had increased AFP levels (0.8%); both were associated with NTDs. Increased AFP levels were found in 44 of 55 samples from group III (80%), and 223 of 1489 samples from group IV (15.0%). CONCLUSION: Routine assessment of AFP in amniotic fluid based on advanced maternal age provides little additional value in the detection of NTDs beyond that of week 20 ultrasound.