Preterm labor

Screening for preterm birth with predictive tests in the normal prenatal population is not commonly practiced, as there are no established interventions to reduce risk in this population. The beneficial role of progesterone, cerclage, and arabin pessary are principally related to women at high risk, such as those with a previous preterm birth.

The low prevalence of preterm birth in a normal population means positive predictive values are low, even with a test that has reasonable sensitivity and specificity. This is confirmed by one study on the predictive accuracy of both cervical length and fetal fibronectin in a low-risk population.[107]Esplin MS, Elovitz MA, Iams JD, et al. Predictive accuracy of serial transvaginal cervical lengths and quantitative vaginal fetal fibronectin levels for spontaneous preterm birth among nulliparous women. JAMA. 2017 Mar 14;317(10):1047-1056. http://www.ncbi.nlm.nih.gov/pubmed/28291893?tool=bestpractice.com

Although these tests remain the two best predictors of preterm birth, they should not be used to screen for risk in normal women. Cervical length and fetal fibronectin continue to have clinical utility in women at risk, such as those with prior preterm birth.