A New Wrinkle in the Prevention of Preterm Delivery Through Cervical Cerclage
Abstract & Commentary
By John C. Hobbins, MD, Professor and Chief of Obstetrics, University of Colorado Health Sciences Center, Denver, is Associate Editor for OB/GYN Clinical Alert.
Dr. Hobbins reports no financial relationship to this field of study.
Synopsis: With normal cervical mucus IL-8, cerclage treatment for cervical shortening may reduce the rate of preterm delivery; but with elevated cervical mucus, IL-8 cerclage may be harmful.
Source: Sakai M, et al. Evaluation of effectiveness of prophylactic cerclage of a short cervix according to interleukin-8 in cervical mucus. Am J Obstet Gynecol. 2006;194:14-19.
In the January issue of the American Journal of Obstetrics and Gynecology an article from Japan appeared that will shed new light on the practice of using cerclage in patients with short cervices. Over a 5-year period 16,508 had transvaginal ultrasound evaluations between 20-24 weeks. A short cervix was defined as a cervical length of less than 25 mm. At the same time every patient in the study also had an assessment of an inflammatory cytokine, interleukin-8 (IL-8) in her cervical mucus.
Two hundred fifty-six patients (1.49%) had short cervices and, based on the attending physicians’ preference (but without the IL-8 information), 165 patients had a cerclage procedure either by McDonald technique (133) or a Shirodkar-like procedure (32). The remaining 81 patients were treated conservatively.
Overall, the rates of preterm birth (PTB) in those 246 patients with short cervices having cerclage and those not having the procedure were the same. However, the presence or absence of the positive cervical IL-8 had a major effect on the results. For example, in those with cervical shortening, the positive IL-8 group had a significantly higher rate of PTB than the normal IL-8 group at < 32 weeks (15% vs 2.4%), < 34 (27.4% vs 6.5%), and < 37 weeks (68.5% vs 38.7%). Also, when comparing those having cerclages with "controls" with short cervices, those with a normal IL-8 concentration had a lower rate of PTB than those without intervention. The most striking finding was that doing a cerclage in the face of a positive IL-8 value resulted in the highest PTB rate before 37 weeks (78%), and a much shorter procedure-to-delivery interval.
Commentary
To stitch or not to stitch? That has been always been the question in a patient who has a past obstetrical history that suggests cervical incompetence. Now that cervical length measurements are often being employed in those at risk for PTB, the picture is certainly no clearer. Individual randomized clinical trials and a recent metaanalysis have not borne out the therapeutic advantage of prophylactic cerclage in those patients with a history suggestive of incompetent cervix or in those with short cervices prior to 24 weeks. Only one study remains that suggests the benefit of performing a cerclage in at-risk patients showing progressive cervical shortening in the mid trimester.1-4
The problem is that only a small percentage of PTBs can be chalked up to a true inability of the cervix to contain the pregnancy. Our lack of success in decreasing PTB stems from the heterogeneity of its cause. For example, it is simplistic to think that every patient presenting with painless early dilation of the cervix or mid-trimester cervical shortening has an incompetent cervix. The cervix responds on command to various hormone and cytokine messages and only occasionally does it passively shorten because it is truly structurally "incompetent." This study definitely lends even more credence to exploring an infectious etiology to preterm delivery before attempting to stop it with tocolytics or a cerclage.
Romero and colleagues have written an excellent companion editorial to the above paper in the same journal.5 He and his group have found that 50% of patients presenting with a clinical story for incompetence cervix will have a documented silent intrauterine infection, and 9% of patients with a short cervix will have a positive amniotic fluid culture. The above study from Japan indicates that non-invasive assessment of cervical inflammation and, indirectly, intrauterine infection through investigation of a cytokine in cervical mucus, may help in excluding patients possibly destined for a cerclage procedure. While showing that doing a cerclage in a patient with a positive IL-8 is certainly not productive, it does suggest that doing it in a patient with a negative IL-8 could be.
Once again, we are reminded that prevention of preterm birth is a complicated process and while making every attempt to keep fetuses in utero is laudable on the surface, in many cases we are interfering with nature’s attempt to get them out before infection and/or cytokines have an irreversible effect on the fetal brain and other organs. That said, this study indicates that perhaps in a small select group of patients we should not completely give up on cerclage.
References
- Berghella V, 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.
- Rust OA, et al. 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.
- Drakeley AJ, et al. Cervical cerclage for prevention of preterm delivery: meta-analysis of randomized trials. Obstet Gynecol. 2003;102:621-627; Erratum in: Obstet Gynecol. 2004;103:201
- Romero R, et al. Infection and labor. VIII. Microbial invasion of the amniotic cavity in patients with suspected cervical incompetence: prevalence and clinical significance. Am J Obstet Gynecol. 1992;167:1086-1091.
- Romero R, et al. The role of cervical cerclage in obstetric practice: can the patient who could benefit from this procedure be identified? Am J Obstet Gynecol. 2006;194:1-9.
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