This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Urethra & Penis, Subject name: Surgery
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? 
Select and explain. 
A. Impairment of the fetus's swallowing mechanism, B. Tumor of the fetus's brain, C. A secretory peptide from the placenta, D. Excess antidiuretic hormone (ADH) from the fetus
A: Impairment of the fetus's swallowing mechanism
Answer: A: Impairment of the fetus's swallowing mechanism 
Explanation: Anencephalus is due to failure of the cephalic part of the neural tube to close off. This condition happens in 1/1000 pregnancies, is four times more common in whites than blacks, and is four times more common in females than males.