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
Bag of membrane ruptures: 
Select and explain. 
A. Before full dilatation of cervix, B. After full dilatation of cervix, C. After head is engaged, D. With excessive show
B: After full dilatation of cervix
Answer: B: After full dilatation of cervix 
Explanation: Membranes usually rupture after full dilatation of cervix or sometimes even beyond, in the second stage.
Early Rupture of Membranes:

Rupture of membranes any time after the onset of labour but before full dilatation of cervix.

Premature Rupture of Membrane:

Rupture of membranes before the onset of labour.
Sometimes the membranes remain intact until completion of delivery, the fetus is then born surrounded by them and the portion covering the head of the newborn infant is known as the Caul.