Clinical Review

The short cervix in pregnancy: Which therapy reduces preterm birth?

OBG Manag. 2003 August;15(8):28-38

References

1. Iams JD. Cervical incompetence. In: Creasy RK, Resnik R, eds. Maternal-Fetal Medicine. 4th ed. Philadelphia, Pa: WB Saunders; 1999;445-464.

2. Guzman ER. Cervical length and spontaneous prematurity: laying the foundation for future interventional randomized trials for the short cervix. Ultrasound Obstet Gynecol. 2001;18:195-199.

3. Guzman ER, Forster JK, Vintzileos AM, et al. Pregnancy outcomes in women treated with elective versus ultrasound-indicated cervical cerclage. Ultrasound Obstet Gynecol. 1998;12:323-327.

4. Berghella V, Hass S, Chervoneva I, Hyslop T. Patients with prior second-trimester loss: prophylactic cerclage or serial transvaginal sonograms? Am J Obstet Gynecol. 2002;187:747-751.

5. Rust OA, Atlas RO, Jones KJ, Benham BN, Balducci J. A randomized trial of cerclage versus no cerclage among patients with ultrasonographically detected secondtrimester preterm dilatation of the internal os. Am J Obstet Gynecol. 2000;183:830-835.

6. Rust OA, Atlas RO, Reed J, van Gaalen J, Balducci J. Revisiting the short cervix detected by transvaginal ultrasound in the second trimester: why cerclage therapy may not help. Am J Obstet Gynecol. 2001;185:1098-1105.

7. Rust OA, Atlas RO, Fischl S, Depuy A, Kimmel S, Hess LW. Does cerclage therapy improve perinatal outcome in patients with a history of previous preterm birth and cervical changes on 2nd trimester transvaginal ultrasound? Am J Obstet Gynecol. 2002;187(suppl):S58.-

8. Iams JD, Johnson FF, Sonek K, et al. Cervical competence as a continuum: a study of ultrasonographic cervical length and obstetric performance. Am J Obstet Gynecol. 1995;174:1097-1106.

9. Hassan SS, Romero R, Berry SM, et al. Patients with an ultrasonographic cervical length ≤15 mm have nearly a 50% risk of early spontaneous preterm delivery. Am J Obstet Gynecol. 2000;182:1458-1467.

10. Iams JD, Goldenberg RL, Meis PJ, et al. The length of the cervix and the risk of spontaneous premature delivery. N Engl J Med. 1996;334:567-572.

11. Taipale P, Hilesmaa V. Sonographic measurement of uterine cervix at 18-22 weeks’ gestation and the risk of preterm delivery. Obstet Gynecol. 1998;92:902-907.

12. Hibbard JU, Tart M, Moawad AH. Cervical length at 16-22 weeks’ gestation and risk for preterm delivery. Obstet Gynecol. 2000;96:972-978.

13. Anderson HF, Nugent CE, Wanty SD, Hayashi RH. Prediction of risk for preterm delivery by ultrasonographic measurement of cervical length. Am J Obstet Gynecol. 1990;163:859-867.

14. Heath VC, Southall TR, Souka AP, Elisseou A, Nicholaides KH. Cervical length at 23 weeks of gestation: prediction of spontaneous preterm delivery. Ultrasound Obstet Gynecol. 1998;12(5):312-317.

15. Berghella 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;181:809-815.

16. Berghella V, Tolasa JE, Kuhlman K. Cervical ultrasound compared with manual examination as a predictor of preterm delivery. Am J Obstet Gynecol. 1997;177:723-730.

17. 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;184:652-655.

18. Heath VC, Daskalakis G, Zagaliki A, Carvalho M, Nicolaides KH. Cervicovaginal fibronectin and cervical length at 23 weeks of gestation:relative risk of early preterm delivery. BJOG. 2000;107:1276-1281.

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;172:660-665.

20. Sonek J, Blumefeld M, Foley M, Johnson F, Iams J. Cervical length may change during ultrasonographic examination. Am J Obstet Gynecol. 1990;162:1355-1357.

21. Sonek JD, Iams JD, Blumefeld M, Johnson F, Landon M, Gabbe S. Measurement of cervical length in pregnancy: comparison between vaginal ultrasonography and digital examination. Obstet Gynecol. 1990;76:172-175.

22. Cook CM, Ellwood DA. A longitudinal study of the cervix in pregnancy using transvaginal ultrasound. BJOG. 1996;103:16-18.

23. Anderson HF. Transvaginal and transabdominal ultrasonography of the uterine cervix during pregnancy. J Clin Ultrasound. 1991;19:77-83.

24. Althuisius SM, Dekker GA, Hummel P, Bekedam D, van Geijn HP. Final results of the Cervical Incompetence Prevention Randomized Cervical Trial (CIPRACT): therapeutic cerclage with bed rest versus bed rest alone. Am J Obstet Gynecol. 2001;185:1106-1112.

25. Colombo DF, Iams JD. Cervical length and preterm labor. Clin Obstet Gynecol. 2000;43:735-745.

26. Heath VC, Souka AP, Erasmus I, Gibb DM, Nicolaides KH. Cervical length at 23 weeks’ gestation: the value of Shirodkar suture for the short cervix. Ultrasound Obstet Gynecol. 1998;12:318-322.

27. Hibbard JU, Snow J, Moawad AH. Short cervical length by ultrasound and cerclage. J Perinatol. 2000;20:161-165.

28. Hassan SS, Romero R, Maymon E, et al. Does cervical cerclage prevent preterm delivery in patients with short cervix? Am J Obstet Gynecol. 2001;184:1325-1331.

They also noted that the likelihood of spontaneous preterm delivery increased exponentially the shorter the cervical measurement. Hibbard et al¹² attained similar findings with cervical measurements obtained at 16 to 22 weeks’ gestation in an unselected population, verifying the value of cervical measurements at an earlier gestational age in predicting preterm delivery.

In a retrospective cohort study, Hassan et al⁹ reviewed cervical measurements in an unselected population between 14 and 24 weeks, and found that close to 50% of gravidas with a cervical length of 15 mm or less delivered earlier than 32 weeks’ gestation. They therefore suggest that cervical length be measured early in the second trimester to obtain more accurate assessment of underlying risk for cervical incompetence.⁹

Interpreting cervical characteristics. As mentioned, other cervical qualities are useful to assess, such as funneling (and measurement of the residual cervix if funneling is present), v-shaped lower uterine segment (FIGURE 2), and dynamic changes with fundal or suprapubic pressure.^3,10,19 Consistency of measurement—with careful attention to both intraoperator and interoperator variability—is vital when using these findings for clinical decision-making.^1,10

Focus screening on women at risk. The sensitivity and predictive value of cervical length improve when screening is limited to populations at greatest risk: women with a history of preterm delivery, cervical surgery, or previous midtrimester loss or cervical incompetence. Conversely, positive and negative predictive values are low when measurements are performed in a low-risk population.¹⁷

Still, determining which gravidas are at highest risk of preterm delivery is a challenge; a careful obstetric history is the most important tool (TABLE).^4,15,16,24 In addition to the factors listed in the table, any history of successful cerclage placement is also significant.²⁵ An extensive history also may offer clues as to what may have caused a shortened cervix in a previous pregnancy. Acquiring old medical records may further clarify the situation.

Unfortunately, the aforementioned trials, while documenting the predictive value of cervical measurements, reveal nothing about specific clinical interventions such as cerclage placement. Rather, they indicate the need for well-designed randomized trials.

The advisability of therapeutic cerclage varies from case to case, but prophylactic cerclage, in general, should be offered to women with a classic history of cervical incompetence or prior cerclage with a successful outcome.

FIGURE 2 Transvaginal ultrasound of shortened cervix with funneling

The cervical length is 1.11 cm with a “U”-shaped funnel measuring 2.51 cm by 1.47 cm.TABLE

Preterm delivery: Factors indicating high risk

History of spontaneous preterm delivery without evidence of contractions History of 1 or more midtrimester losses History of multiple cervical manipulations: – Conization or loop electrosurgical excision procedures – Multiple dilation and curettage procedures – Multiple pregnancy terminations Uterine anomaly Multiple gestations Polyhydramnios History of exposure to diethylstilbestrol First- or second-trimester vaginal bleeding

History of spontaneous preterm delivery without evidence of contractions
History of 1 or more midtrimester losses
History of multiple cervical manipulations:
- – Conization or loop electrosurgical excision procedures
- – Multiple dilation and curettage procedures
- – Multiple pregnancy terminations
Uterine anomaly
Multiple gestations
Polyhydramnios
History of exposure to diethylstilbestrol
First- or second-trimester vaginal bleeding

Management options

Once a short cervix has been diagnosed, the obstetrician faces a morass of conflicting data on how to proceed. After reviewing the patient’s history to identify any obvious risk factors, attempt to rule out uterine contractions, ruptured membranes, and clinical or subclinical infection. Once these and any other causes are excluded, the primary management options are bed rest and placement of cervical cerclage. Unfortunately, this is an issue of great controversy, with no definitive evidence on which strategy is best.

Based on the data available, we suggest the following cervical surveillance (FIGURE 1):

Perform initial cervical measurements in high-risk patients at 14 to 24 weeks’ gestation. Women with cervical lengths exceeding 26 mm should be reassessed in 2 to 3 weeks.
Women with a cervical length between 21 and 25 mm should be placed on reduced physical activity with remeasurement in 2 weeks.
Patients with a length between 16 and 20 mm should be placed on strict bed rest with remeasurement in 1 week.
Only women with a cervical length of 15 mm or less should be considered for therapeutic cerclage.^9,24

No evidence supports measuring cervical length or placing a cerclage in the low-risk patient.

Cerclage versus bed rest: Ambiguous evidence

Several nonrandomized retrospective observational trials of cerclage placement versus bed rest in the general obstetric population reported conflicting results. For example, Heath et al²⁶ studied a low-risk obstetric population in Great Britain that underwent transvaginal measurements of cervical length. Women with lengths of 15 mm or less were managed expectantly (n=21) or had a Shirodkar cerclage placed (n=22). Only 5% in the cerclage group delivered prior to 32 weeks’ gestation, compared with 52% in the expectantly managed group. In a general obstetric population, Hibbard et al²⁷ also found an increase in the duration of pregnancy (2 weeks) among women who underwent cerclage placement for a cervical length less than 26 mm (n=43), compared with those who had no cerclage placed (n=42).