Beigh, M., M. F. Mir, R. Amin, and S. Shafi. “Role of Transvaginal Ultrasound in Predicting Preterm Labor in Singleton Pregnancies”. International Journal of Reproduction, Contraception, Obstetrics and Gynecology, vol. 7, no. 2, Jan. 2018, pp. 561-5, doi:10.18203/2320-1770.ijrcog20180172.