Cervical incompetence refers to a painless spontaneous dilatation of the cervix and is a common cause of second trimester pregnancy failure.
The estimated incidence varies geographically and generally thought to be around 1-1.5% of all pregnancies 1,15.
Typically cervical incompetence manifests in the second trimester. Patients at high risk for preterm delivery include those with:
- idiopathic (most common)
- uterine anomalies 7
- exposure to diethylstilbestrol (DES)
- previous cervical trauma or surgery
- previous recurrent spontaneous or therapeutic abortion
- previous premature delivery
- multifetal pregnancy
- connective tissue disorder (Ehlers-Danlos syndrome)
- fetal fibronectin (fFN) test on vaginal mucus: needs to be done before trans-vaginal scanning is attempted
Transvaginal, translabial or transperineal sonography is most commonly used to assess the cervix.
It should be emphasized that the appearance of the cervix may change during the examination and therefore multiple observations are recommended. Excessive pressure with the probe and an overly distended bladder may give false reassurance by artificially lengthening and narrowing the cervical canal. It is also useful to measure the worst finding.
Transvaginal scanning is required. In a late 1st trimester scan, an opening of the cervical os at rest or in response to fundal pressure is considered an early feature 18
- bulging of the fetal membranes into a widened internal os (considered the most reliable sign 9)
- the appearance of this can worsen from a T-shape to a Y-shape to a V-shape and finally to a U-shape (see cervical incompetence mnemonic)
- if there is complete bulging, it can give an hourglass-type appearance
- shortening of the cervical canal
- in severe cases, there may be fetal parts or cord that extend through the os
It is used as a prognostic indicator for the risk of preterm labor progressing into preterm delivery.
The cervical length (CL) is obtained by measuring the endocervical canal from the internal cervical os to the external cervical os.
The normal cervix should be at least 30 mm in length. Cervical incompetence is variably defined, however, a cervical length of <25 mm at or before 24 weeks is often used. The risk of preterm delivery is inversely proportional to cervical length ref:
- 18% for <25 mm
- 25% for <20 mm
- 50% for <15 mm
In borderline cases, transfundal pressure may be used to confirm the diagnosis.
The presence of cervical funnelling is also an important finding. Greater than 50% funnelling before 25 weeks is associated with 80% risk of preterm delivery.
Sonographic determination of the residual closed length of the cervix may be measured if there is:
- known complicating preterm premature rupture of membranes
- known hourglass type membranes
- active vaginal bleeding
Treatment and prognosis
Management options can be controversial, with conflicting results, particularly regarding the efficacy of a cerclage placement as treatment. Bed-rest, tocolysis, cerclage (tracheloplasty), transabdominal suture placement, and administration of steroids to accelerate fetal lung maturity are all treatment options to be considered. A recent meta-analysis suggests that cerclage is effective in reducing preterm births by 26% in singleton pregnancies.
If the cervical length is <30 mm (<3 cm), close interval follow up is recommended.
- 1. Callen PW. Ultrasonography in obstetrics and gynecology. W B Saunders Co. (2000) ISBN:0721681328. Read it at Google Books - Find it at Amazon
- 2. 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 (1): 181-9. doi:10.1097/01.AOG.0000168435.17200.53 - Pubmed citation
- 3. Kaakaji Y, Nghiem HV, Nodell C et-al. Sonography of obstetric and gynecologic emergencies: Part I, Obstetric emergencies. AJR Am J Roentgenol. 2000;174 (3): 641-9. AJR Am J Roentgenol (full text) - Pubmed citation
- 4. Hricak H, Chang YC, Cann CE et-al. Cervical incompetence: preliminary evaluation with MR imaging. Radiology. 1990;174 (3): 821-6. Radiology (abstract) - Pubmed citation
- 5. Hertzberg BS, Kliewer MA, Farrell TA et-al. Spontaneously changing gravid cervix: clinical implications and prognostic features. Radiology. 1995;196 (3): 721-4. Radiology (abstract) - Pubmed citation
- 6. Hassan S, Romero R, Hendler I et-al. A sonographic short cervix as the only clinical manifestation of intra-amniotic infection. J Perinat Med. 2006;34 (1): 13-9. doi:10.1515/JPM.2006.002 - Free text at pubmed - Pubmed citation
- 7. Troiano RN, Mccarthy SM. Mullerian duct anomalies: imaging and clinical issues. Radiology. 2004;233 (1): 19-34. doi:10.1148/radiol.2331020777 - Pubmed citation
- 8. Maldjian C, Adam R, Pelosi M et-al. MRI appearance of cervical incompetence in a pregnant patient. Magn Reson Imaging. 1999;17 (9): 1399-402. Magn Reson Imaging (link) - Pubmed citation
- 9. Ludmir J. Sonographic detection of cervical incompetence. Clin Obstet Gynecol. 1988;31 (1): 101-9. - Pubmed citation
- 10. Confino E, Mayden KL, Giglia RV et-al. Pitfalls in sonographic imaging of the incompetent uterine cervix. Acta Obstet Gynecol Scand. 1986;65 (6): 593-7. - Pubmed citation
- 11. Parulekar SG, Kiwi R. Dynamic incompetent cervix uteri. Sonographic observations. J Ultrasound Med. 1988;7 (9): 481-5. J Ultrasound Med (abstract) - Pubmed citation
- 12. Jackson G, Pendleton HJ, Nichol B et-al. Diagnostic ultrasound in the assessment of patients with incompetent cervix. Br J Obstet Gynaecol. 1984;91 (3): 232-6. - Pubmed citation
- 13. Edozien LC. The incompetent cervix--a review. Br J Clin Pract. 1992;46 (4): 264-7. - Pubmed citation
- 14. Merz E, Bahlmann F. Ultrasound in obstetrics and gynecology. Thieme Medical Publishers. (2005) ISBN:1588901475. Read it at Google Books - Find it at Amazon
- 15. Waloch M. Cervical cerclage in the treatment of cervical incompetence in Zambian women. Clin Exp Obstet Gynecol. 1996;23 (4): 255-62. - Pubmed citation
- 16. Feingold M, Brook I, Zakut H. Detection of cervical incompetence by ultrasound. Acta Obstet Gynecol Scand. 1984;63 (5): 407-10. - Pubmed citation
- 17. Brook I, Feingold M, Schwartz A et-al. Ultrasonography in the diagnosis of cervical incompetence in pregnancy-a new diagnostic approach. Br J Obstet Gynaecol. 1981;88 (6): 640-3. - Pubmed citation
- 18. Macdonald R, Smith P, Vyas S. Cervical incompetence: the use of transvaginal sonography to provide an objective diagnosis. Ultrasound Obstet Gynecol. 2001;18 (3): 211-6. doi:10.1046/j.1469-0705.2001.00459.x - Pubmed citation
- 19. Guzman ER, Pisatowski DM, Vintzileos AM et-al. A comparison of ultrasonographically detected cervical changes in response to transfundal pressure, coughing, and standing in predicting cervical incompetence. Am. J. Obstet. Gynecol. 1997;177 (3): 660-5. Am. J. Obstet. Gynecol. (link) - Pubmed citation
- 20. Bluth EI. Ultrasound, a practical approach to clinical problems. Thieme Publishing Group. (2008) ISBN:3131168323. Read it at Google Books - Find it at Amazon