Repeat measurement of cervical length after successful tocolysis.

Objective: To measure the ultrasonographic cervical length in undelivered women after successful tocolysis for preterm labor, and to determine whether this could improve the predictive value of cervical length measured before initiation of tocolysis on the risk of preterm delivery.

Methods: This was a prospective study of patients admitted and treated for uterine contractions at 24(+0) to 33(+6) weeks of gestation with a cervical length of 26 mm or less by transvaginal ultrasonography on admission. Intravenous tocolysis was stopped when delivery was delayed by 48 hours, and cervical length was remeasured before discharge. The primary outcome was preterm delivery, defined by a delivery before 37 weeks. Predictive analysis was based on logistic models, with estimated odds ratios and 95% confidence interval.

Results: One hundred and nine patients were included in the study. The median (first, third quartile) cervical length on admission was 18 (13, 22) mm. The median (first, third quartile) variation in cervical length after tocolysis was stopped was 3 (0, 8) mm, and ranged from -13 to 26 mm. The median (first, third quartile) time interval from tocolysis to delivery was 53.0 (35.0, 70.0) days, with 45 (41.3%) patients delivered before 37 weeks. After adjustment for cervical length before admission and parity and gestational age on admission, the assessment of the variation in cervical length after successful tocolysis did not improve the predictive value of transvaginal sonography for the risk of preterm delivery (odds ratio 0.97; 95% confidence interval 0.90-1.03; P = .27).

Conclusion: To repeat ultrasonographic cervical length measurement after successful tocolysis for preterm labor is useless.