Aim: To describe the longitudinal changes in canal length at 16-35 weeks' gestation in cases of twin pregnancy with preterm labor and delivery.
Methods: We studied 22 cases of twin pregnancy that were delivered at < 36 weeks and/or that underwent preterm labor requiring tocolysis. We also studied 44 cases of twin pregnancy delivered at > or = 36 weeks without tocolysis (non-tocolysis twin pregnancy). Controls were 82 cases of normal singleton pregnancy. Canal length was longitudinally measured using transvaginal ultrasonography. The observational period of 16-35 weeks was divided into 4-week periods for analysis.
Results: From 28 to 31 weeks onwards the canal length of non-tocolysis twin pregnancies was shorter than that of normal singleton pregnancies (P < 0.05). The canal length of twin pregnancies with preterm labor and delivery was shorter than that of non-tocolysis twin pregnancies at 16-19 weeks and decreased rapidly until 24-27 weeks (P < 0.01).
Conclusions: A short canal length at 16-19 weeks followed by rapid canal length shortening in the second trimester are specific characteristics in preterm labor and delivery of twin pregnancies. Sequential measurements of canal length in the second trimester starting at < 20 weeks may be a suitable parameter to predict preterm labor and delivery in twin pregnancies.