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
Which of the following is the cut-off value of cervical length at 24 weeks of gestation for prediction of preterm delivery? 
Select and explain. 
A. 0.5 cm, B. 1.5 cm, C. 2.5 cm, D. 3.5 cm
C: 2.5 cm
Answer: C: 2.5 cm 
Explanation: Factors required for the prediction of preterm labour includes: presence of symptoms of preterm labour, uterine contraction of >= 4 per hour, cervical length <=2.5cm, presence of fibronectin in cervicovaginal discharge between 24-34 weeks, Bishop score >=4, cervical dilation >2cm and effacement of 80%, vaginal bleeding and prior preterm bih. Ref: Textbook of Obstetrics By D.C. Dutta 6th Edition, Pages 314-315