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
Labour is said to be prolonged when duration of latent stage of labour crosses: 
Select and explain. 
A. 12 hours, B. 18 hours, C. 20 hours, D. 36 hours
C: 20 hours
Answer: C: 20 hours 
Explanation: labour pattern nullipara multipara prolonged latent phase >20 hrs >14 hrs protracted active phase dilatation <1.2 cm/hr <1.5 cm/hr protracted descent <1 cm/hr <2 cm/hr arrest of dilatation >2 hr >2 hr arrest of descent >1 hr >1 hr