Aim: To determine whether or not the change in cervical length (CL) over time is valuable in predicting spontaneous preterm delivery (SPTD) in asymptomatic twin pregnancies with a normal mid-trimester CL (>25 mm).
Methods: This was a prospective study including 190 consecutive asymptomatic twin gestations with a CL>25 mm at 20-24 weeks. The women underwent an initial CL measurement at the time of routine ultrasound examination between 20 and 24 weeks' gestation, followed 4-5 weeks later by a repeat CL measurement. The primary outcome measure was SPTD at <32 completed weeks' gestation. Multicollinearity was a concern in the multivariable model since change in CL and follow-up CL were highly correlated.
Results: The rate of SPTD at <32 weeks was 4.2%. Multiple logistic regression analyses demonstrated that the change in CL and the follow-up CL were significantly associated with SPTD before 32 weeks after adjusting for baseline covariate such as in vitro fertilization. The best cut-off values for the prediction of SPTD at <32 weeks' gestation were 13% for the change in CL with a sensitivity of 87.5% and a specificity of 63.2%. There was no significant difference in the area under the receiver operating characteristic curves between the change in CL and the follow-up CL.
Conclusions: A greater change in CL is a good predictor of SPTD in asymptomatic twin pregnancies with a normal mid-trimester CL. However, the change in CL cannot provide data beyond the follow-up CL. In the setting of a normal mid-trimester CL, a follow-up CL measurement should be considered in asymptomatic twin pregnancies.