This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Abnormal labor, Subject name: Gynaecology & Obstetrics
Risk of preterm delivery is increased if cervical length is less than : 
Select and explain. 
A. 2.5 cm, B. 3.0 cm, C. 3.5 cm, D. 4.0 cm
A: 2.5 cm
Answer: A: 2.5 cm 
Explanation: During pregnancy cervical length of <2.5cm and internal os of 1cm increases the chance of miscarriage Reference: Dutta's Textbook of Obstetrics 7th edition page no 169