This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
Pathognomonic of ectopic pregnancy is : 
Select and explain. 
A. Purple hemorrhagic pregnancy in lower vagina, B. Decidual casts, C. Chadwick sign, D. Postcoital hemorrhage
B: Decidual casts
Answer: B: Decidual casts 
Explanation: Decidual casts