Can the optimal cervical length for placing ultrasound-indicated cerclage be identified?

Objective To assess a continuum of cervical length (CL) cut-offs for the efficacy of ultrasound-indicated cerclage in women with previous spontaneous preterm birth (PTB). Methods This was a planned secondary analysis of a multicenter randomized clinical trial of ultrasound-indicated cerclage for the prevention of PTB in high-risk women. The efficacy of cerclage for preventing recurrent PTB < 35, < 32 and < 24 weeks' gestation was assessed using multivariable logistic regression analysis. Odds ratios (ORs) and CIs were estimated for a range of CL cut-offs using bootstrap regression. The 2.5th and 97.5th percentiles of bootstrapped ORs determined the CIs. Results were illustrated using smoothed curves superimposed on estimated ORs by CL cut-off. Results Of 301 women with a CL < 25 mm, 142 underwent ultrasound-indicated cerclage and 159 did not have cerclage placement. The few cases with CL < 10mm limited the evaluation to CL cut-offs between < 10mm and < 25 mm. For PTB < 35 weeks, ORs in women with a cerclage and CL < 25mm were statistically significantly lower than in those without cerclage, and efficacy was maintained at smaller CL cut-offs. Results were similar for PTB < 32 weeks. For PTB < 24 weeks, results differed, with ORs increasing toward unity (no benefit), with wide CIs, for CL cut-offs between < 10mm and < 15 mm, attributed to the small number of births < 24 weeks. Conclusions The efficacy of ultrasound-indicated cerclage in women with previous spontaneous PTB varies by action point CL cut-off and by PTB gestational age of interest. Cerclage significantly reduces the risk of PTB < 35 and < 32 weeks, at CL cut-offs between < 10mm and < 25 mm, with the greatest reduction at shorter CL, affirming that women with prior spontaneous PTB and a short CL are appropriate candidates for ultrasound-indicated cerclage. Copyright (C) 2015 ISUOG. Published by John Wiley & Sons Ltd.