Commentary on ‘Sequential cervical length screening in pregnancies after LLETZ conisation: a retrospective analysis’
Although emphasised by Pils et al., the use of cervical sonography to predict the risk of preterm birth or to identify candidates for treatment with cerclage or progesterone is not the principal contribution of cervical imaging. Rather, the importance of cervical ultrasound is that it has provided the opportunity to observe the parturitional process at the cervix and decidual–membrane interface. These observations have overturned previous paradigms that emphasised myometrial activity, membrane rupture, and early cervical effacement as independent pathways to preterm birth. The association of a short cervix with an increased risk of preterm birth was initially interpreted in that paradigm as evidence of a continuum of competence, to which LLETZ was a surgical contributor, and for which cerclage, a surgical cure, was prescribed. After more than a decade of unsuccessful attempts to find a combination of cervical length threshold and reproductive history that could distinguish ‘cervical insufficiency’ from ‘preterm labour’, the results of two landmark studies produced a revelation: a medical therapy, progesterone, was shown to be effective for a short cervix (Fonseca et al., N Engl J Med 2007;357:462–469), whereas surgical treatment helped women with the shortest cervical length, of less than 15 mm, where a greater benefit would be expected when the cervix was 15–25 mm (Owen et al., Am J Obstet Gynecol 2009;201:375.e1–375.e8). These studies have made it clear that, with some exceptions, a short cervix is evidence of parturition in progress, a process that is more biochemical than biophysical, and that in the most severe cases is evident well before the now outdated 20-week delineation between ‘miscarriage’ and ‘preterm labor’.
Studies of paired measurements of cervical length, as reported by Pils et al., are welcome because they allow for the assessment of the timing of onset and the rate of progression of this process. Looking at cervical length over time rather than in a specific gestational age window produces different interpretations of the same data. For example, the 1996 National Institute of Child Health and Human Development (NICHD) Preterm Prediction Study concluded that a short cervix at 22–24 and at 26–28 weeks of gestation is a predictor of subsequent spontaneous preterm birth before 35 weeks of gestation (Iams et al., N Engl J Med 1996;334:567–573). A re-examination of paired cervical length measurements from that study at 22–24 and 26–28 weeks of gestation revealed that cervical change had already occurred before 22–24 weeks of gestation in women destined to deliver after 28 weeks of gestation, and that the rate of cervical change before spontaneous preterm birth was similar, regardless of the eventual clinical presentation as preterm labour or membrane rupture (Iams et al., Am J Obstet Gynecol 2011;205:130.e1–e6). The parturitional process was evident weeks before both presentations.
The LEETZ procedure inserts another variable into the interpretation of short cervix. Pils et al., have contributed more than they may have realised by including repeated cervical measurements in their analysis. The reader is invited to read the paper again keeping the ‘short cervix is parturition in progress’ model in mind.
Declaration of interests
I have no conflicts of interest - no commercial relationships, advisory panels, speakers bureaus, stocks/investments in medical products.
I receive contract funding to perform clinical research studies from the NICHD, Cincinnati Childrens Med Center, & CaseWestern/MetroHealth, and stipends & royalties from Elsevier as editor of Am J Obstet Gynecol & of Creasy/Resnik textbook
Ohio State University, Columbus, OH, USA