Objective To investigate the association between mid‐trimester residual cervical length (CL) and the risk of preterm birth in pregnancies after abdominal radical trachelectomy (RT). Design Retrospective cohort study. Setting University hospital. Population A total of 33 deliveries after 22 weeks’ gestation in 30 women who underwent abdominal RT including prophylactic cervical cerclage and perinatal care between January 2002 and May 2016. Methods The association between mid‐trimester residual CL (the distance between the cerclage and the external cervical os) and gestational age at delivery was investigated. Receiver–operating characteristics (ROC) curve analysis was performed to estimate the optimal cut‐off values of the mid‐trimester residual CL for the prediction of preterm birth. Main outcome measures Preterm birth before 34 weeks’ gestation. Results Mid‐trimester residual CL showed a significant correlation with gestational age at delivery (r = 0.36, P < 0.05). There was a significant difference in residual CL between women who did and those who did not give birth before 34 weeks (P < 0.05). Mid‐trimester residual CL < 13 mm was a good predictor of birth before 34 weeks, with a sensitivity of 67%, specificity of 75%, positive predictive value of 55% and negative predictive value of 86% (area under ROC curve, 0.75). Conclusions Mid‐trimester residual CL is significantly correlated with gestational age at delivery. Residual CL assessment could be used to reassure physicians and women that there is only a small chance of preterm birth in pregnancies after abdominal RT. Tweetable Mid‐trimester residual cervical length is a good predictor of preterm birth after radical trachelectomy. Tweetable Mid‐trimester residual cervical length is a good predictor of preterm birth after radical trachelectomy.