[Biochemical markers of neural tube closure defects during the second half of pregnancy].

Increasing number of amniocentesis done during the second half of gestation with indication "signe d'appel" made necessary for authors to study amniotic fluid markers in late pregnancy. Normal evolution curve must be established with samples obtained after 20 weeks gestation. Study reveals more false-negative results with AFP than before 20 weeks. AChE remains constantly positive in cases with NTD, band aspect being specific. For other malformations, AChE positivity seems inconstant, with a different aspect. Some normal gestation cases can be associated with faint AChE band.