Objective  To explore the influence of lifestyle of pregnant women before and after pregnancy on preterm birth and to provide evidences for maternal and infant health care.

  Methods  From September 2012 to October 2014, we enrolled 11 311 pregnant women having regular prenatal examinations at Wuhan Women and Children Medical Center in Wuhan city of Hubei province into a prospective cohort. We extracted relevant information from the participants' medical records and health care manual for pregnant women and conducted surveys at deliveries of the participants with a self-designed questionnaire. Chi-square test and Fisher's exact test were used to analyze the differences of qualitative data. Unconditional logistic regression was used in multivariate analysis.

  Results  Higher incidence rates of preterm birth were observed in the participants smoking during six month before the pregnancy (14.94%) and in those having exercise less than two days per week during third trimester (9.77%). Logistic regression analysis revealed following risk factors for preterm birth among the participants: total annual income of husband and wife less than 30 000 RMB yuan (compared to that of ≥ 200 000: odds ratio OR = 2.50, 95% confidence interval 95% CI: 1.25 – 4.99), smoking during 6 months before pregnancy (OR = 2.42, 95% CI: 1.30 – 4.48), husbandly education of junior high school and below (compared to that of college and above: OR = 2.08, 95% CI: 1.60 – 2.69), husbandly education of senior high school and technical secondary school (compared to that of college and above: OR = 1.45, 95% CI: 1.16 – 1.82), maternal education of junior high school and below (compared to that of college and above: OR = 1.93, 95% CI: 1.51 – 2.47), and having exercise less than two days per week in third trimester (compared to having exercise every day: OR = 1.81, 95% CI: 1.52 – 2.15).

  Conclusion  For pregnant women, having exercise less than two days per week in third trimester and smoking during 6 months before the pregnancy could increase the risk of preterm birth.