[Assessment of AFP in amniotic fluid: comparison of three automated techniques]

Abstract

Ultrasound scanning is useful to detect neural tube defect (NTD) but scarcely distinguished between closed NTD and open NTD, which had very different prognosis. An amniotic fluid punction is thus mandatory to search for an increase in alpha foeto protein (AFP) levels and for the presence of acetylcholinesterase which identified open NTD. However, AFP levels fluctuate both with the gestational age and the assay used. Our aim was to establish normative values for AFP in amniotic fluid in the second half of pregnancy using three different immunoassays and to improve their clinical relevance. Amniotic fluid punctions were performed on 527 patients from 9 week of gestation (WG) to 37 WG either for maternal age, Trisomy 21 screening, increase in nucal translucency (control group, n = 527) or for suspicion of neural tube defect or abdominal defect (n = 5). AFP was measured using the immunoassay developed for serum AFP on the Access 2 system, the Immulite 2000 and the Advia Centaur. Results were expressed in ng/ml, multiple of the median (MoM) and percentiles. AFP decrease by 1.5 fold between 9 and 19 WG. When NTD was suspected, an increase in anmniotic AFP was observed (from 2.5 MoM to 9.3 MoM) confirming an open NTD. In conclusion, the assay developed on those 3 automates is suitable for the measurement of AFP in amniotic fluid.