A irst concern with screening surrounds the eicacy of interventions to improve perinatal outcomes once cervical length screening has isolated at-risk gravidas. Of interventions, cervical cerclage and administration of vaginal progesterone have both been evaluated. Vaginal progesterone for this indication is discussed on page 817. For prophylactic cerclage in women with prior preterm births and shortened cervices, many studies have failed to show superior primary outcomes. But, piecemeal subgroup analyses from the trials have been subsequently used as the basis for recommendations in current practice guidelines regarding cervical length assessment and consideration for cerclage placement. A second concern is the accuracy and utility of the screening test, especially in low-risk women, who represent most of the population with preterm birth (p. 813).
To address this issue in low-risk women, Esplin and colleagues (2017) prospectively studied 9410 nulliparas with singleton pregnancies. Universal screening of sonographically measured cervical length and quantitative measurement of vaginal fFN levels were evaluated as predictors of women who would spontaneously deliver before 37 weeks. hese measures had poor predictive performance as a screening test. In fact, all screening modalities had relative low sensitivity and low positive-predictive values. Based on these indings, routine use of these screening tests in this low-risk population is not recommended. Bloom and Leveno (2017) subsequently critiqued the use of transvaginal cervicalrlength screening in low-risk women and the promulgation of consensus guidelines. As described in Chapter 1 (p. 7), they highlighted the staggering costs encumbering the health-care system in the United States as a result of such strategies.
Prevention of preterm birth remains an elusive goal. Still, may be achievable.
Of options, cerclage placement may be used to prevent pre term birth in at least three circumstances. First, the procedure may beneit women who have a history of recurrent midtrimester losses and who are diagnosed with cervical insuiciency. A second instance is the woman identiied during sonographic examination to have a short cervix. The third indication is a "rescue" cerclage, done emergently when cervical incompetence is recognized in women with threatened preterm labor.
As is the case for virtually all obstetrical conditions, an accurate history is critical for management decisions. For recurrent abortion from cervical incompetence, historical clues are outlined in Chapter 18 (p. 354). For women with a short cervix incidentally detected by sonography, the beneit of cerclage placement appears directly related to whether the woman has a history of prior preterm birth. In those without a prior preterm birth, cerclage for a sonographically detected short cervix alone ofers no advantage. To and associates (2004) screened 47,123 women and randomly assigned the 253 women with cervices < 15 mm, with or without a history of preterm birth, to cerclage or no cerclage. he frequency of preterm delivery before 33 weeks did not difer signiicantly. In contrast, women with a sonographically diagnosed short cervix and a history of preterm birth may beneit. Owen and colleagues (2009) randomly assigned 302 women with prior preterm birth and with a short cervix-deined as length <25 mm-to cerclage or no procedure. The primary study outcome was not supported by the intervention. However, women with a cervical length < 15 mm delivered before 35 weeks signiicantly less oten following cerclage compared with women with no cerclage-30 versus 65 percent. his study suggested that recurrent preterm birth could be prevented in a subset of women with asymptomatic singleton gestations with both previous pre term birth and short cervical length.