Given the availability of several effective interventions for the prevention of PTB, TVUS cervical screening for high-risk patients is recommended. Routine TVUS screening is also supported by the American College of Obstetricians and Gynecologists and Society for Maternal-Fetal Medicine [36,37]. Although TVUS is not contraindicated in the setting of placenta previa, it should be performed using real-time imaging as the probe is advanced. The safety in this setting is based on the presumption that the angle between the cervix and the vaginal probe is sufficient to prevent the probe from inadvertently slipping into the cervix and that real-time imaging is used throughout the procedure to assess the relationship between the probe tip and the cervix [33]. Cervical Cerclage Patients who have undergone history-indicated cerclage for cervical insufficiency represent a subset of high-risk patients. In these patients with a history of one or more second trimester losses, cerclage placement may be offered during the early second trimester. In one recent study screening cerclage patients by TVUS until 26 weeks, a shorter CL below the cerclage and cervical funneling were shown to be associated with a higher rate of PTB [38]. In a separate study evaluating postcerclage patients between 18 and 24 weeks, cervical funneling was the only variable independently associated with increased risk of PTB before 34 weeks [39]. Although these and other studies suggest that short CL and cervical funneling are associated with higher rates of PTB in patients with cerclage, the Society for Maternal-Fetal Medicine does not recommend routine surveillance for this subset of high-risk patients because there is insufficient data supporting a clinical benefit to screening [37].
Assessment of Gravid Cervix. Given the availability of several effective interventions for the prevention of PTB, TVUS cervical screening for high-risk patients is recommended. Routine TVUS screening is also supported by the American College of Obstetricians and Gynecologists and Society for Maternal-Fetal Medicine [36,37]. Although TVUS is not contraindicated in the setting of placenta previa, it should be performed using real-time imaging as the probe is advanced. The safety in this setting is based on the presumption that the angle between the cervix and the vaginal probe is sufficient to prevent the probe from inadvertently slipping into the cervix and that real-time imaging is used throughout the procedure to assess the relationship between the probe tip and the cervix [33]. Cervical Cerclage Patients who have undergone history-indicated cerclage for cervical insufficiency represent a subset of high-risk patients. In these patients with a history of one or more second trimester losses, cerclage placement may be offered during the early second trimester. In one recent study screening cerclage patients by TVUS until 26 weeks, a shorter CL below the cerclage and cervical funneling were shown to be associated with a higher rate of PTB [38]. In a separate study evaluating postcerclage patients between 18 and 24 weeks, cervical funneling was the only variable independently associated with increased risk of PTB before 34 weeks [39]. Although these and other studies suggest that short CL and cervical funneling are associated with higher rates of PTB in patients with cerclage, the Society for Maternal-Fetal Medicine does not recommend routine surveillance for this subset of high-risk patients because there is insufficient data supporting a clinical benefit to screening [37].