This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Types of Genetic Disorders, Subject name: Pediatrics
Which of the following is a cause of decreased maternal serum a protein - 
Select and explain. 
A. Neural tube defects, B. Fetal demise, C. Hepatitis, D. Aneuploidy
D: Aneuploidy
Answer: D: Aneuploidy 
Explanation: | Maternal serum a - Fetoprotein Decreased Maternal Serum a fetoprotein Twins Neural tube defects Intestinal atresia Hepatitis Nephrosis Fetal demise Incorrect gestational age Trisomies Aneuploidy