<prompt> During her eighth month of pregnancy, a 29-year-old woman is noted to have polyhydramnios. Further testing shows anencephalus. Polyhydramnios in this patient is caused by which of the following?Impairment of the fetuss swallowing mechanismTumor of the fetuss brainA secretory peptide from the placentaExcess antidiuretic hormone ADH from the fetus  <response>: Anencephalus is due to failure of the cephalic part of the neural tube to close off. This condition happens in 11000 pregnancies, is four times more common in whites than blacks, and is four times more common in females than males. 