This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Obstetrics, Subject name: Gynaecology & Obstetrics
Hormone responsible for decidual reaction and arias Stella reaction in ectopic pregnancy is - 
Select and explain. 
A. Oestrogen, B. Progesterone, C. HCG, D. HPL
B: Progesterone
Answer: B: Progesterone 
Explanation: Hormone responsible for decidual reaction and arias Stella reaction in Ectopic as well as Intrauterine pregnancy is Progesterone Arias stella reaction is the localized hypersecretory endometrium seen in ectopic pregnancy.