1. Cunningham G, Leveno KJ, Bloom SL, Spong CY, et al. Williams's obstetrics. 25th ed. new York: Appleton and lange, 2018;803-807
2. World Health Organization 2019، Available data in 2019/5/21
3. The Role of Body, Mind, and Environment in Preterm Birth: Mind the Gap
4. Martin JA, Hamilton BE, Osterman MJK, Driscoll AK, Drake P. Births: Final Data for 2015. National Vital Statistics Reports 2017; 66: 1
5. Prevalence of preterm labor in Iran: A systematic review and meta-analysis