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

In a retrospective review of an obstetric population with cervical lengths of 15 mm or less, Hassan et al²⁸ compared women receiving cerclage (n=25) with those who did not (n=45). In contrast to the 2 trials just mentioned, cervical cerclage failed to decrease the rate of spontaneous preterm delivery. Moreover, patients with a cerclage had an increased incidence of premature rupture of membranes.

In a nonrandomized prospective observational trial of women at high risk for preterm delivery, Berghella et al¹⁵ reported that those undergoing cerclage (n=39) for cervical length less than 25 mm and/or for 25% funneling fared no better than women who did not undergo cerclage placement (n=24).

Randomized prospective controlled trials. Only 2 such trials have been reported to date, and their design and patient populations differ.

Althusius et al²⁴ studied a high-risk population in the Cervical Incompetence Prevention Randomized Cervical Trial (CIPRACT), which involved primary randomization to determine the effects of prophylactic cerclage, and secondary randomization to determine the effects of therapeutic cerclage. Women with a history of preterm delivery before 34 weeks who had a “classic” history of cervical incompetence were allocated to prophylactic cerclage or no cerclage in the late first or early second trimester. Thus, these gravidas already met the diagnosis of cervical incompetence. Both groups were then followed with serial measurements of cervical length. A second randomization to therapeutic cerclage or bed rest occurred if a cervical length less than 25 mm was found before 27 weeks’ gestation. This trial showed a statistically significant greater mean gestational age and improved pregnancy outcomes among women in both groups who received a cerclage, suggesting that therapeutic cerclage is a viable management option in at-risk women with cervical shortening. Moreover, the study design of primary and secondary randomization offers a sound strategy for management.

To address the value of therapeutic cerclage, Rust et al^5-7 designed a prospective, randomized trial of both high-risk and low-risk women with second-trimester shortened cervical measurements with funneling or a total cervical length less than 25 mm. These women were allocated to therapeutic cerclage or bed rest. Prior to randomization, all women underwent cervical and urinary cultures and amniotic fluid analysis to exclude underlying intra-amniotic infection. Both groups then were followed with weekly transvaginal cervical measurements. A rescue cerclage was placed if prolapsing membranes occurred in either group.

Although decreasing cervical length was associated with poorer pregnancy outcomes, cervical cerclage did not result in a statistically significant greater mean gestational age or improved perinatal outcome, contradicting the results reported in the CIPRACT trial. Furthermore, patients who needed rescue cerclage had the worst outcomes. One explanation may be that the CIPRACT trial included only patients with a history of cervical incompetence, whereas Rust et al included low-risk and high-risk women unexpectedly noted to have a shortened cervix—patients more akin to the woman described at the beginning of this article, and a more likely scenario for most obstetricians.

Until better evidence is available, the limited number of randomized, controlled trials addressing the issue of shortened cervical length should guide management. Using this information, several institutions have initiated “cervical surveillance” programs in which clinicians perform serial ultrasounds to assess changes in cervical length over time. The most recent results from the ongoing randomized trial by Rust et al⁷—the best evidence to date in both low-risk and high-risk women—offer the promise of answers to this issue.

The authors report no financial relationship with any companies whose products are mentioned in this article.