During the prenatal period, a 19 year old female is concerned about possible neural tube defects, based upon the appearance of a "lemon sign" by ultrasonography. Which of the following laboratory tests will most strongly suggest the presence of a neural tube defect:
A Decreased human chorionic gonadotropin
B Hypochromic, microcytic anemia
C Decreased serum folate
D Increased alpha-fetoprotein
E Positive serologic test for syphilis
(D) CORRECT. Alpha-fetoprotein represents half of fetal serum protein, and this protein can gain access to amnionic fluid through a neural tube defect. From the amnionic fluid, the alpha-fetoprotein can appear in maternal serum by crossing the placenta. Adults normally do not have circulating alpha-fetoprotein.
M.D., PGY-3 Internal Medicine