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Association between pregnancy body mass index in normal cases and in cases with preterm birth was studied in a hospital record based cohort. 400 patients were studied for BMI in pregnancy, 200 cases of preterm labour in Group A and 200 without preterm labour in Group B. Data was analysed and correlated for preterm delivery and its relation to BMI. BMI was categorised as <18.5 (underweight); 18.5–24.9 (normal); 25.0–29.9(overweight); 30.0–34.9 (obese I); 35.0–39.9 (obese II); and 40.0 (obese III) .It was found that there is increased risk of preterm labour in patients with increase body > mass index.