Increased amnionic fluid alpha-fetoprotein due to a holoacardium amorphous twin.

Amnionic fluid alpha-fetoprotein measurement was employed as a screening test for neural tube defects in a pregnancy only at risk due to advanced maternal age. The alpha-fetoprotein concentration was elevated more than 10 standard deviations above the mean and was found to be caused by a holoacardium amorphous twin. A normal female fetus was also present. Various causes of elevated alpha-fetoprotein concentration in amnionic fluid are discussed.