Does Cervical Conization Predispose a Patient to Preterm Birth?
Abstract & Commentary
By John C. Hobbins, MD, Professor of Obstetrics and Gynecology, 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: To estimate whether the time interval between cervical conization and subsequent pregnancy is associated with risk of preterm birth.
Source: Hines K, Simhan HN. Time from cervical conization to pregnancy and preterm birth. Obstet Gynecol. 2007; 109:314-319.
It has not been clear as to whether a cervical conization truly predisposes a patient to preterm birth (PTB). The authors of this enlightening paper set out to see if the interval between the procedure and subsequent conception had any effect on the incidence of PTB.
Hines and Simhan analyzed data over a three-year period on patients having had treatment for cervical dysplasia at Magee Women's Hospital in Pittsburgh. They compared pregnancy outcomes from 114 patients having had LEEP, large loop excisions or cold knife conizations, with a control group of 962 patients who were worked up with colposcopic directed biopsies, but received no treatment. Their endpoint was simple—a subsequent birth occurring between 20 and 36 weeks of gestation. The authors were particularly interested in the interval between conization and conception, the size of the cervical specimen at the time of conization, and the incidence of premature rupture of membranes (PROM).
Interestingly, there was no difference in the incidence of PTB between the two groups, suggesting that conization, in general, did not predispose patients to early delivery. Also, the incidence of PROM was essentially the same in both groups (1.8%), and, although it is unclear from the paper whether the size of the excised tissue made a difference, the average size of the excised tissue was 1.9 cm. This does suggest that conization, at least soon after the procedure, has a significant effect on cervical length.
The major finding was that there was a significant difference in PTB in those with short excision to conception intervals. For example, those conization patients having a PTB had an average interval of 2.5 months, compared with an average 10.5 month interval in those conization patients who delivered at term.
Commentary
First, as opposed to another recent study, there did not appear to be an overall difference in the rate of PTB in conization patients compared with controls. This is not surprising, since the most important structural portion of the cervix (regarding the job of containing the pregnancy) would be the area in the neighborhood of the endocervix, and not the one that was excised. However, the outer third is the first barrier that bacteria will encounter when attempting to move up the canal and, until the area is stabilized after excision, it may be vulnerable to infection while undergoing its own reparative processes. Some studies correlating cervical length, in general, with PROM have catalyzed the thinking that the decreased distance between vaginal bacteria and the membranes lends itself to weakening of these membranes over the cervix. However, the Hines study showed no difference in PROM between those who would undergo a conization and those who did not.
The take-home message here is that the cervical length is less of a problem than the time interval between treatment and initiation of pregnancy, and, therefore, patients should try to wait at least twelve months before contemplating pregnancy after any type of conization.
References
- Hines K, et al. Time from cervical conization to pregnancy and preterm birth. Obstet Gynecol. 2007; 109:314-319.
- Crane JM, et al. Transvaginal ultrasonography in the prediction of preterm birth after treatment for cervical intra-epithelial neoplasia. Obstet Gynecol. 2006;107: 37-44.
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