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
Extreme preterm is defined as 
Select and explain. 
A. 34-36 weeks, B. 32-33 weeks, C. 28-31 weeks, D. < 28 weeks
D: < 28 weeks
Answer: D: < 28 weeks 
Explanation: Preterm labor is defined as one where the labor stas before 37th completed week, counting from the first day of the last menstrual period Lower limit of gestation is - 20 weeks in developed countries 28 weeks in developing countries Ref: Dutta Obs 9e pg 294.