Asgharnia, Maryam, Tahereh Varasteh, and Davoud Pourmarzi. “Inter-Pregnancy Interval and the Incidence of Preterm Birth”. Journal of Family and Reproductive Health (July 18, 2020): 52-56. Accessed September 20, 2020. https://jfrh.tums.ac.ir/index.php/jfrh/article/view/1272.