This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Anatomy
Main source of prolactin in amniotic fluid is : 
Select and explain. 
A. Decidua, B. Synctiotrophoblast, C. Cytotrophoblast, D. Yolksac of fetus
A: Decidua
Answer: A: Decidua 
Explanation: Decidua is the main source of prolactin present in amniotic fluid. Decidual prolactin is not confused with human placental lactogen(hpl) which is produced only by the synctiotrophoblast. Ref:Williams Obs - 24 e pg 88.