The role of cervical ultrasound in the management of preterm labor.

Amaç

Different strategies have been developed to refine the risk of preterm delivery in asymptomatic patients. Transvaginal sonography (TVS) has been used in this indication to measure and examine the length and shape of the cervix.
TVS of the cervix in clinical studies conducted in asymptomatic women at high risk of preterm delivery:
Three ultrasound signs are suggestive of cervical incompetence :
Dilatation of the internal os (I.O.); sacculation or prolapse of the membranes into the cervix (with shortening of the functional cervical length), either spontaneously or induced by transfundal pressure; and/or short cervix in the absence of uterine contractions. TVS has clearly demonstrated that cerclage leads to a measurable increase in cervical length which may contribute to the success of this procedure in reducing the risk of preterm delivery. Several non-randomized interventional studies among patients with cervical incompetence have been published. They have defined a new group of patients requiring cerclage when they show progressive cervical modifications on TVS. In other studies, cerclage performed on the basis of cervical changes on TVS did not prevent premature delivery. One prospective randomized trial in asymptomatic high-risk women has shown 2 benefits in cerclage following TVS indications : i)
this would generate less prophylactic cerclages in high risk women; and ii) therapeutic cerclage before 27 weeks may reduce the incidence of premature delivery before 34 weeks.
TVS of the cervix in clinical studies among patients at low risk of preterm delivery:
The risk of preterm delivery is inversely correlated with the cervical length. Routine TVS of the cervix performed between 18 and 22 weeks can help identify patients at risk of preterm delivery. However, given the low prevalence of preterm births, screening would generate either a high false positive rate or a low sensitivity. One non-randomized interventional study among patients with a short cervix on routine ultrasound examination found a lower risk of delivery before 32 weeks in the cerclage group than in the expectant management group. However, the only prospective randomized trial published in a low risk population has shown that cerclage of a modified cervix on TVS in the second trimester did not improve perinatal outcome.

Sonuç

Although the level of evidence is still low, there does appear to be a benefit in performing a cerclage rather than continuing with expectant management in cases with ultrasound appearance of cervical incompetence. Ultrasound can be offered to reduce the indications of cerclage in cases where the situation is uncertain.
Within the general obstetric population, TVS might help selecting asymptomatic but high risk women, however, the benefit associated with cerclage for sonographic indication is not demonstrated.
Key-words : Preterm labor. Preterm delivery. Cervical length. Cervical incompetence. Cerclage. Ultrasound