The May issue of Ultrasound in Obstetrics & Gynecology has a special focus on preterm birth, with relevant articles on the effectiveness of established and emerging screening methods and their implementation in clinical practice, as well as preventative methods such as pessary or cervical cerclage.
This issue of the Journal illustrates the range of predictive tests and interventions for preterm birth (PTB) that are under investigation. An Opinion piece by Shennan gives an overview in the context of existing literature of some of the relevant articles included in this issue, highlighting the often conflicting evidence, and advising that more input from the academic community is required to elucidate the subtleties in differing efficacies of both prediction and prevention of PTB.
Prediction of preterm birth
Short cervical length (CL) on second-trimester ultrasound has been shown to be one of the best predictors for PTB in singleton pregnancy. In this issue, an Original Article by Wulff et al. investigated whether short CL in the second or third trimesters could be predicted on combined first-trimester screening at 11–14 weeks’ gestation, finding that there is an association between first-trimester CL and risk of short cervix in the second trimester. An Original Article by Fichera et al. assessed the predictive value of mid-gestation sonographic CL measurement for spontaneous PTB in asymptomatic triplet pregnancy, finding it to be a poor predictor in such pregnancies.
There are also emerging techniques for cervical microstructure assessment that could provide additional information, aiding the prediction of PTB. One such method investigated in an Original Article by Baños et al. is sonographic cervical consistency index measured in the second trimester in low-risk pregnancy. The authors found that cervical consistency index is a better predictor of spontaneous PTB < 37 weeks than is CL. Another technique, described by Baños et al. in this issue, is quantitative analysis of sonographic cervical texture in mid-pregnancy. It was found that mid-trimester cervical-texture-based score is associated independently with spontaneous PTB.
Other screening methods for PTB include biomarker analysis. In this issue, an Original Article by Melchor et al. compared the performance of the placental alpha microglobulin-1 (PAMG-1) and fetal fibronectin (fFN) tests for the prediction of spontaneous PTB in symptomatic women, finding them to have similar negative predictive values, but that PAMG-1 has a superior positive predictive value.
Whilst there are promising results for these PTB screening methods, whether they should be implemented depends upon cost–benefit analysis. For example, Wulff et al. found that, in their low-risk population, to prevent one case of spontaneous PTB < 34 weeks, more than 1500 women would need to have CL measured at the 19–21-week anomaly scan, calling into question its cost-effectiveness. An Original Article by van Baaren et al. evaluated cost-effectiveness of a screening method that combines CL measurement and fFN testing in symptomatic women at 24–34 weeks’ gestation. The authors found that performing additional fFN testing when CL is between 15 and 30 mm is a viable and cost-saving strategy.
Prevention of preterm birth
Use of a cervical pessary has been studied for possible prevention of PTB in singleton pregnancy with short sonographic CL, although current evidence of its efficacy is conflicting. This issue’s Journal Club article by Dugoff et al. is a Randomized Controlled Trial investigating whether pessary use can indeed prevent PTB in such women without prior spontaneous PTB, finding it to be ineffective (download the accompanying Journal Club slides). Conversely, an Original Article by van ‘t Hooft et al. provided a 3-year follow-up of the ProTWIN trial in which it was found that cervical pessary prevented PTB and improved neonatal outcome in women with multiple pregnancy and CL <38 mm. The follow-up study found that cervical pessary strongly improved survival of the children without affecting neurodevelopment at 3 years’ corrected age.
Cervical cerclage is used to correct cervical insufficiency in pregnancy in order to prevent PTB and associated complications. This issue’s Picture of the Month by Ichizuka et al. describes a case in which the use of three-dimensional transvaginal sonography facilitated observation of an intra-abdominal cervical-isthmus cerclage.
Also to look out for this month is a Virtual Issue on Prediction and Prevention Preterm Birth, containing a selection of relevant articles from UOG.
Coming up in the next issue is a series of papers reporting on pre-eclampsia.