Background and Objectives Height, abnormal BMI & weight gain play a very important role in the outcome of pregnancy that hard labor or dystocia is one of the main reasons of the mortality of mothers. This study was done to determine the spread of hard labor and maternal height, BMI and weight gain, the factors related to that in women referring to the public maternity hospitals of Qom in 2006. Methods The present research is a 6-month descriptive- analytical study conducted upon the 4325 females ready for labor referring to the public hospitals of Qom. The instrument for collecting data was the questionnaire which was completed with observation, interview and examination. Finally, the data were analyzed by descriptive and inferential statistical procedures of X2, t-test, correlation & linear regression (OR). Results The results showed that hard labor had a meaningful statistical relationship with the height of mother, BMI and weight gain. Maximum dystocia was present in women with height<150cm, BMI>35, weight gain >16 kg (p<0/001). Conclusion The results showed that excessive weight gain, BMI and mother’s height were associated with dystocia . By considering that up till now, no comprehensive epidemiologic study has been reported in Iran about labor dystocia, and with regard to the dangerous impacts of mother and fetus, further studies are recommended.