Hiersch and colleagues contribute a thorough description of cervical length measurements abstracted from charts of women who presented with threatened preterm labor. Their report was welcomed by our reviewers as a useful contribution to the care of women with this clinical presentation. As the editor assigned to review this paper, I also endorsed publication but for a different reason, seeing it as an example, perhaps one of the last of its kind, of an analysis of cervical ultrasound measurements presented without a corresponding measure of time. Consideration of the relation of cervical length to the outcome of pregnancy has, from its beginnings in the previous century, been dominated by single measurements taken at specified gestational ages, rather than rates of change, eg, “The mean (±SD) cervical length at 24 weeks was 34.0 ± 7.8 mm for nulliparous women and 36.1 ± 8.4 mm for parous women; the comparable measurements at 28 weeks were 32.6 ± 8.1 for nulliparous women and 34.5 ± 8.7 for parous women.” Hiersch and colleagues continue that tradition, describing cervical length within specified gestational age intervals to evaluate the likelihood of preterm birth within 7 and 14 days of measurement. Studies of the rate of cervical length changes over time, eg, by Guzman et al in 1998 and Naim et al in 2002, did not gain many followers, probably at least in part because the investigators found analyses of rates over time to be more difficult than static measurements. Fortunately, more enlightened minds have recently engaged rates of cervical change over time to study the parturitional process. These reports support changes in understanding “threatened preterm labor” less as a distinct event than as a process that can occur over weeks or months at variable rates of cervical change. Viewed this way, “short cervix” has become a moment in time (your cervix is shortening), instead of a biological fact (you have a short cervix), and “cervical insufficiency” can be thought of as “early onset, rapidly progressive preterm parturition.” The implications of understanding variation in the onset and rate of change in cervical length as representing differences in the pace of preterm parturition are substantial, eg, the 20-week boundary between “miscarriage” and preterm birth could disappear. Preterm labor or preterm ruptured membranes with pain signify contractions without prior cervical preparation; preterm labor with little or no pain suggests prior cervical change.

Such conceptual discussions may influence the current interpretation of static measurements, but could measurement of the rate of change ever become part of clinical care? Recent work suggests that it could. Etemadi et al recently described “…a novel device designed specifically to take fluorescence and impedance measurements throughout pregnancy, with the end goal of fusing and trending these measurements to form an early diagnosis of preterm labor.” Stay tuned for more from these and other researchers who are focused on continuous measurement of cervical change over time! Static measurement of cervical length may soon join the wristwatch and the slide rule.