How are a Long Cervix and Having a C-Section Related?
A study in the current issue of the New England Journal of Medicine has been widely reported with headlines such as “Longer Cervix Associated with Higher C-Section Risk” and “Cervical Length Predicts C-Section.” The authors, performing their research at several hospitals in the UK, used data on women having their first baby during the study period who had cervical length measure sometime between 22-24 weeks, and ultimately delivered at term.
Information on mid-pregnancy cervical length was compared with medical records for the 27,472 women, including information on “the mode of delivery, the gestational age at birth, whether the patient was in labor, whether the onset of labor was spontaneous or induced, and the indications for operative delivery. Outcome data for the infant were also recorded, including whether the birth was a live birth or stillbirth, the birth weight, and the sex.” The authors then tried to determine whether cervical length predicted c-section, and whether the indication for c-section was failure to progress.
The authors grouped women into four groups by cervical length, and found that those with the shortest mid-pregnancy cervical length were least likely to have a c-section, with likelihood of the surgery increasing for each increasing length group. Ultimately, 5,542 women (or about 20%) delivered via cesarean section, and for 83.3% of these, failure to progress was listed as one of the indications for the procedure.
Although this was a planned second look at the data from the authors’ original study, certain data that might be interesting/important were not available, such as how long the women were in labor, dilation and effacement progress, whether standardized definitions of failure to progress were in place and whether these definitions were always followed across different physicians and hospitals. It’s also not entirely clear how often “failure to progress” was the main indication for c-section, as opposed to “one of” the indications, so we don’t really know if other, possibly more important, things were happening.
Rita Rubin of the new USA Today health blog also touches on another question, which is whether the generally accepted duration of labor is maybe not appropriate on an individual basis. Is it possible that women who start out with a longer cervix simply need a little extra time to fully efface and dilate? Could this need for extra time lead to a “failure to progress” label? Although the authors found that mid-pregnancy cervical length predicted c-section, and that “the increased risk of this event among women who had a long cervix in mid-pregnancy was explained by the increased risk of poor progress during labor,” several questions seem to remain about how and why that happened.
Citation: Smith GC, Celik E, To M, Khouri O, Nicolaides KH; Fetal Medicine Foundation Second Trimester Screening Group. Cervical length at mid-pregnancy and the risk of primary cesarean delivery. N Engl J Med. 2008 Mar 27;358(13):1346-53. PMID: 18367737