Value of serial cervical length measurement in prediction of spontaneous preterm birth in post-conization pregnancy without short mid-trimester cervix

Serial cervical length (CL) measurement in mid-trimester is recommended in post-conization pregnancy to estimate the risk of spontaneous preterm birth (SPTB). A short mid-trimester cervix (CL < 25 mm) has been considered as a strong predictor for SPTB. However, the low incidence of short cervix limits the utility of mid-trimester CL measurement in prediction of SPTB. A great proportion of women who develop SPTB don’t have a short mid-trimester cervix. Therefore, this study was aimed to investigate the additional value of serial CL measurement in predicting SPTB in addition to detecting short cervix alone. A total of 613 post-conization pregnant women who did not have short mid-trimester cervix between January 2004 and January 2014 were included in this study. Serial CL measurements were taken by transvaginal ultrasound at three timepoints (A: 13 + 0–15 + 6 weeks, B: 16 + 0–18 + 6 weeks, and C: 20 + 0–22 + 6 weeks). Eight parameters were analyzed for predicting SPTB, including CL measurements at different timepoints (CL(A), CL(B), CL(C)), the maximum and minimum CL measurements (CL(MAX), CL(MIN)), and the percentage change in CL measurement between different timepoints (%ΔCL(AB), %ΔCL(BC), %ΔCL(AC)). After univariate and multivariate analysis, CL(MAX) and %ΔCL(AC) were independent variables in predicting SPTB. Lower CL(MAX) (OR [95%CI]: 0.92 [0.90–0.93]) and higher %ΔCL(AC) (OR [95%CI]: 1.05 [1.01–1.09]) were related to an increasing risk of SPTB. In conclusion, our study for the first time in literature reported the value of serial CL measurement in prediction of SPTB in post-conization pregnancy without short mid-trimester cervix. In the subpopulation of pregnant women who did not have short mid-trimester cervix, CL(MAX) and %ΔCL(AC) were of value in predicting SPTB, which warranted further investigations.