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Second trimester evaluation of cervical length for prediction of spontaneous preterm birth


This topic will describe the normal distribution of cervical length, provide a clinical definition for a short cervix, and discuss our approach and technique for cervical length screening.


Cervical shortening (effacement) is one of the first steps in the parturition process, preceding labor by several weeks. As cervical length decreases in the second trimester, the risk of spontaneous preterm birth increases [1-5], especially when effacement occurs early in the second trimester [6]. Because effacement begins at the internal cervical os and progresses caudally [1,5], it is often detected on ultrasound examination before it can be appreciated on physical examination. The cause of preterm cervical shortening is often unclear. It has been attributed to several sources, including occult uterine activity, uterine overdistention, congenital or acquired cervical insufficiency, decidual hemorrhage, infection, inflammation, and biological variation.


Normally, cervical length is stable between 14 and 28 weeks of gestation and is described by a normal, bell-shaped curve [1,7]:

15 mm – 2nd centile

20 mm – 5th centile


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Literature review current through: Sep 2014. | This topic last updated: Oct 29, 2014.
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  1. Iams JD, Goldenberg RL, Meis PJ, et al. The length of the cervix and the risk of spontaneous premature delivery. National Institute of Child Health and Human Development Maternal Fetal Medicine Unit Network. N Engl J Med 1996; 334:567.
  2. Taipale P, Hiilesmaa V. Sonographic measurement of uterine cervix at 18-22 weeks' gestation and the risk of preterm delivery. Obstet Gynecol 1998; 92:902.
  3. Hibbard JU, Tart M, Moawad AH. Cervical length at 16-22 weeks' gestation and risk for preterm delivery. Obstet Gynecol 2000; 96:972.
  4. Heath VC, Southall TR, Souka AP, et al. Cervical length at 23 weeks of gestation: prediction of spontaneous preterm delivery. Ultrasound Obstet Gynecol 1998; 12:312.
  5. Owen J, Yost N, Berghella V, et al. Can shortened midtrimester cervical length predict very early spontaneous preterm birth? Am J Obstet Gynecol 2004; 191:298.
  6. Berghella V, Roman A, Daskalakis C, et al. Gestational age at cervical length measurement and incidence of preterm birth. Obstet Gynecol 2007; 110:311.
  7. Fonseca EB, Celik E, Parra M, et al. Progesterone and the risk of preterm birth among women with a short cervix. N Engl J Med 2007; 357:462.
  8. Kushnir O, Vigil DA, Izquierdo L, et al. Vaginal ultrasonographic assessment of cervical length changes during normal pregnancy. Am J Obstet Gynecol 1990; 162:991.
  9. Andersen HF, Nugent CE, Wanty SD, Hayashi RH. Prediction of risk for preterm delivery by ultrasonographic measurement of cervical length. Am J Obstet Gynecol 1990; 163:859.
  10. Zorzoli A, Soliani A, Perra M, et al. Cervical changes throughout pregnancy as assessed by transvaginal sonography. Obstet Gynecol 1994; 84:960.
  11. Zilianti M, Azuaga A, Calderon F, et al. Monitoring the effacement of the uterine cervix by transperineal sonography: a new perspective. J Ultrasound Med 1995; 14:719.
  12. Gramellini D, Fieni S, Molina E, et al. Transvaginal sonographic cervical length changes during normal pregnancy. J Ultrasound Med 2002; 21:227.
  13. Crane JM, Hutchens D. Transvaginal sonographic measurement of cervical length to predict preterm birth in asymptomatic women at increased risk: a systematic review. Ultrasound Obstet Gynecol 2008; 31:579.
  14. Hassan SS, Romero R, Vidyadhari D, et al. Vaginal progesterone reduces the rate of preterm birth in women with a sonographic short cervix: a multicenter, randomized, double-blind, placebo-controlled trial. Ultrasound Obstet Gynecol 2011; 38:18.
  15. Society for Maternal-Fetal Medicine Publications Committee, with assistance of Vincenzo Berghella. Progesterone and preterm birth prevention: translating clinical trials data into clinical practice. Am J Obstet Gynecol 2012; 206:376.
  16. Romero R, Nicolaides K, Conde-Agudelo A, et al. Vaginal progesterone in women with an asymptomatic sonographic short cervix in the midtrimester decreases preterm delivery and neonatal morbidity: a systematic review and metaanalysis of individual patient data. Am J Obstet Gynecol 2012; 206:124.e1.
  17. Iams JD, Johnson FF, Sonek J, et al. Cervical competence as a continuum: a study of ultrasonographic cervical length and obstetric performance. Am J Obstet Gynecol 1995; 172:1097.
  18. Berghella V, Kuhlman K, Weiner S, et al. Cervical funneling: sonographic criteria predictive of preterm delivery. Ultrasound Obstet Gynecol 1997; 10:161.
  19. Hassan SS, Romero R, Berry SM, et al. Patients with an ultrasonographic cervical length < or =15 mm have nearly a 50% risk of early spontaneous preterm delivery. Am J Obstet Gynecol 2000; 182:1458.
  20. Rust OA, Atlas RO, Kimmel S, et al. Does the presence of a funnel increase the risk of adverse perinatal outcome in a patient with a short cervix? Am J Obstet Gynecol 2005; 192:1060.
  21. Goldenberg RL, Iams JD, Mercer BM, et al. The preterm prediction study: the value of new vs standard risk factors in predicting early and all spontaneous preterm births. NICHD MFMU Network. Am J Public Health 1998; 88:233.
  22. Vaisbuch E, Romero R, Mazaki-Tovi S, et al. The risk of impending preterm delivery in asymptomatic patients with a nonmeasurable cervical length in the second trimester. Am J Obstet Gynecol 2010; 203:446.e1.
  23. Moroz LA, Simhan HN. Rate of sonographic cervical shortening and the risk of spontaneous preterm birth. Am J Obstet Gynecol 2012; 206:234.e1.
  24. Iams JD, Cebrik D, Lynch C, et al. The rate of cervical change and the phenotype of spontaneous preterm birth. Am J Obstet Gynecol 2011; 205:130.e1.
  25. Fox NS, Rebarber A, Klauser CK, et al. Prediction of spontaneous preterm birth in asymptomatic twin pregnancies using the change in cervical length over time. Am J Obstet Gynecol 2010; 202:155.e1.
  26. Berghella V, Baxter JK, Hendrix NW. Cervical assessment by ultrasound for preventing preterm delivery. Cochrane Database Syst Rev 2013; 1:CD007235.
  27. Owen J, Yost N, Berghella V, et al. Mid-trimester endovaginal sonography in women at high risk for spontaneous preterm birth. JAMA 2001; 286:1340.
  28. Goldenberg RL, Iams JD, Miodovnik M, et al. The preterm prediction study: risk factors in twin gestations. National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. Am J Obstet Gynecol 1996; 175:1047.
  29. Vendittelli F, Mamelle N, Munoz F, Janky E. Transvaginal ultrasonography of the uterine cervix in hospitalized women with preterm labor. Int J Gynaecol Obstet 2001; 72:117.
  30. Visintine J, Berghella V, Henning D, Baxter J. Cervical length for prediction of preterm birth in women with multiple prior induced abortions. Ultrasound Obstet Gynecol 2008; 31:198.
  31. Airoldi J, Berghella V, Sehdev H, Ludmir J. Transvaginal ultrasonography of the cervix to predict preterm birth in women with uterine anomalies. Obstet Gynecol 2005; 106:553.
  32. Berghella V, Pereira L, Gariepy A, Simonazzi G. Prior cone biopsy: prediction of preterm birth by cervical ultrasound. Am J Obstet Gynecol 2004; 191:1393.
  33. Rafael TJ. Short Cervical Length. In: Preterm Birth: Prevention and Management, Berghella V. (Ed), Wiley-Blackwell, New York 2010.
  34. Guzman ER, Walters C, O'reilly-Green C, et al. Use of cervical ultrasonography in prediction of spontaneous preterm birth in triplet gestations. Am J Obstet Gynecol 2000; 183:1108.
  35. Iams JD, Goldenberg RL, Mercer BM, et al. The preterm prediction study: can low-risk women destined for spontaneous preterm birth be identified? Am J Obstet Gynecol 2001; 184:652.
  36. Mella MT, Berghella V. Prediction of preterm birth: cervical sonography. Semin Perinatol 2009; 33:317.
  37. Committee on Practice Bulletins—Obstetrics, The American College of Obstetricians and Gynecologists. Practice bulletin no. 130: prediction and prevention of preterm birth. Obstet Gynecol 2012; 120:964.
  38. American College of Obstetricians and Gynecologists. ACOG Practice Bulletin No. 101: Ultrasonography in pregnancy. Obstet Gynecol 2009; 113:451.
  39. Lim K, Butt K, Crane JM. SOGC Clinical Practice Guideline. Ultrasonographic cervical length assessment in predicting preterm birth in singleton pregnancies. J Obstet Gynaecol Can 2011; 33:486.
  40. Orzechowski KM, Boelig RC, Baxter JK, Berghella V. A universal transvaginal cervical length screening program for preterm birth prevention. Obstet Gynecol 2014; 124:520.
  41. Cahill AG, Odibo AO, Caughey AB, et al. Universal cervical length screening and treatment with vaginal progesterone to prevent preterm birth: a decision and economic analysis. Am J Obstet Gynecol 2010; 202:548.e1.
  42. Werner EF, Han CS, Pettker CM, et al. Universal cervical-length screening to prevent preterm birth: a cost-effectiveness analysis. Ultrasound Obstet Gynecol 2011; 38:32.
  43. Berghella V, Odibo AO, To MS, et al. Cerclage for short cervix on ultrasonography: meta-analysis of trials using individual patient-level data. Obstet Gynecol 2005; 106:181.
  44. Goya M, Pratcorona L, Merced C, et al. Cervical pessary in pregnant women with a short cervix (PECEP): an open-label randomised controlled trial. Lancet 2012; 379:1800.
  45. Glanc P, Andreotti RF, Lee SI, et al. ACR Appropriateness Criteria® assessment of gravid cervix. Ultrasound Q 2011; 27:275.
  46. Hernandez-Andrade E, Romero R, Ahn H, et al. Transabdominal evaluation of uterine cervical length during pregnancy fails to identify a substantial number of women with a short cervix. J Matern Fetal Neonatal Med 2012; 25:1682.
  47. To MS, Skentou C, Cicero S, Nicolaides KH. Cervical assessment at the routine 23-weeks' scan: problems with transabdominal sonography. Ultrasound Obstet Gynecol 2000; 15:292.
  48. Saul LL, Kurtzman JT, Hagemann C, et al. Is transabdominal sonography of the cervix after voiding a reliable method of cervical length assessment? J Ultrasound Med 2008; 27:1305.
  49. Stone PR, Chan EH, McCowan LM, et al. Transabdominal scanning of the cervix at the 20-week morphology scan: comparison with transvaginal cervical measurements in a healthy nulliparous population. Aust N Z J Obstet Gynaecol 2010; 50:523.
  50. Friedman AM, Srinivas SK, Parry S, et al. Can transabdominal ultrasound be used as a screening test for short cervical length? Am J Obstet Gynecol 2013; 208:190.e1.
  51. Mason GC, Maresh MJ. Alterations in bladder volume and the ultrasound appearance of the cervix. Br J Obstet Gynaecol 1990; 97:457.
  52. Berghella V, Bega G, Tolosa JE, Berghella M. Ultrasound assessment of the cervix. Clin Obstet Gynecol 2003; 46:947.
  53. Althuisius SM, Dekker GA, Hummel P, et al. Cervical incompetence prevention randomized cerclage trial: emergency cerclage with bed rest versus bed rest alone. Am J Obstet Gynecol 2003; 189:907.
  54. Rust OA, Atlas RO, Jones KJ, et al. A randomized trial of cerclage versus no cerclage among patients with ultrasonographically detected second-trimester preterm dilatation of the internal os. Am J Obstet Gynecol 2000; 183:830.
  55. To MS, Alfirevic Z, Heath VC, et al. Cervical cerclage for prevention of preterm delivery in women with short cervix: randomised controlled trial. Lancet 2004; 363:1849.
  56. Owen J, Hankins G, Iams JD, et al. Multicenter randomized trial of cerclage for preterm birth prevention in high-risk women with shortened midtrimester cervical length. Am J Obstet Gynecol 2009; 201:375.e1.
  57. Berghella V, Odibo AO, Tolosa JE. Cerclage for prevention of preterm birth in women with a short cervix found on transvaginal ultrasound examination: a randomized trial. Am J Obstet Gynecol 2004; 191:1311.
  58. Hui SY, Chor CM, Lau TK, et al. Cerclage pessary for preventing preterm birth in women with a singleton pregnancy and a short cervix at 20 to 24 weeks: a randomized controlled trial. Am J Perinatol 2013; 30:283.
  59. Owen J, Neely C, Northen A. Transperineal versus endovaginal ultrasonographic examination of the cervix in the midtrimester: a blinded comparison. Am J Obstet Gynecol 1999; 181:780.
  60. Berghella V, Talucci M, Desai A. Does transvaginal sonographic measurement of cervical length before 14 weeks predict preterm delivery in high-risk pregnancies? Ultrasound Obstet Gynecol 2003; 21:140.
  61. Conoscenti G, Meir YJ, D'Ottavio G, et al. Does cervical length at 13-15 weeks' gestation predict preterm delivery in an unselected population? Ultrasound Obstet Gynecol 2003; 21:128.
  62. Ludmir J. Sonographic detection of cervical incompetence. Clin Obstet Gynecol 1988; 31:101.
  63. Berghella V, Owen J, MacPherson C, et al. Natural history of cervical funneling in women at high risk for spontaneous preterm birth. Obstet Gynecol 2007; 109:863.
  65. Romero R, Schaudinn C, Kusanovic JP, et al. Detection of a microbial biofilm in intraamniotic infection. Am J Obstet Gynecol 2008; 198:135.e1.
  66. Kusanovic JP, Espinoza J, Romero R, et al. Clinical significance of the presence of amniotic fluid 'sludge' in asymptomatic patients at high risk for spontaneous preterm delivery. Ultrasound Obstet Gynecol 2007; 30:706.
  67. Bujold E, Pasquier JC, Simoneau J, et al. Intra-amniotic sludge, short cervix, and risk of preterm delivery. J Obstet Gynaecol Can 2006; 28:198.
  68. Boyer A, Cameron L, Munoz-Maldonado Y, et al. Clinical significance of amniotic fluid sludge in twin pregnancies with a short cervical length. Am J Obstet Gynecol 2014.
  69. Yost NP, Owen J, Berghella V, et al. Second-trimester cervical sonography: features other than cervical length to predict spontaneous preterm birth. Obstet Gynecol 2004; 103:457.