Tanmoun, N., Raungrongmorakot, K., Ruangvutilert, P., Boriboonhirunsarn, D., Tontisirin, P. and Butsansee, W. 2017. Correlation of Cervical Length Obtained from Transperineal Ultrasonography, Transvaginal Ultrasonography and Digital Examination. Thai Journal of Obstetrics and Gynaecology. 15, 3 (Apr. 2017), 137–144.