2Zorzoli A, Soliani A, Perra M, et al. Cervical changes throughout pregnancy as assessed by transvaginal sonography.Obstet Gynecol, 1994,84:960- 963.
3Iams JD, Goldenberg RL, Meis PJ, et al.The Length of the cervix and the risk of spontaneous premature delivery.N Engl J Med, 1996, 334:567 - 571.
4Gudrun ER, Mellon C, Vintzileos AM, et al. Longitudinal assessment of endoeervieal length between 15 and 24 weeks,gestation in women at risk for pregnancy loss or preterm birth. Obste Gynecol, 1998,92:31 -35.
5Callen PW. Ultrasonography in Obstetrics and Gynecology.4^th edition. Philadephia WB Sauders company,2000.577 - 598.
6Rand L,Norwitz ER.Current controversies in cervical cerclage.Seminars in perinatology,2003,27(1):73~85.
7James H.harger,MD.Cerclage and cervical insufficiency:an evidence-based analysis.Obstet and Gynecol 2002;100 1313~1327.
8Hassan SS,Romero R,Berry SM et al.Patients with an ultrasonographic cervical length <15mm have nearly a 50% risk of early spontaneous preterm delivery.Am J Obstet Gynecol 2000,182:1458~1467.
9Berghella V.Daly SF,Tolosa JE,et al.Prediction of preterm delivery with transvaginal ultrasonography of the cervix in patients with high-risk pregnancies:does cerclage prevent prematurity ? Am J Obstet Gynecol 1999,181:1809~1815.
10Rust OA,Atlas RO,Jones KL,et al.A randomizes trial of cerclage versus no cerclage among patients with ultrasonographicallly detected second-trimester preterm dilatation of the internal os.AM J Obstet Gynecol 2000,183:830~835.