Unusual increase in amniotic fluid alpha fetoprotein and trisomy 13

From 10 observations of trisomy 13, 3 presented an elevated amniotic fluid alpha-fetoprotein level considered as unusual in 2 cases, superior to cut-off level in the other case. Macroscopic examination of the three fetus could not reveal a cause of AFP elevation, neural tube defect or abdominal wall defect. The authors discuss the role of an undetected abnormality such as minor scalp defect with very thin membrane and for one case false-negative result of Kleihauer test.