Objective: Our objective was to evaluate the relationship between the interpregnancy interval (IPI) and next-pregnancy mid-trimester cervical length (CL) in women at high risk for recurrent spontaneous preterm birth (SPTB).Methods: Retrospective review identified high-risk women, defined as a prior SPTB <36 weeks, who began scheduled serial transvaginal sonographic CL screening at 16-18 weeks gestation between December 2008 and November 2010. All CL assessment ended by 226/7 weeks, and weekly 17-hydroxyprogesterone caproate, 250 mg IM, was recommended to all patients. Details of the prior and current pregnancy were collected, and regression models were used to evaluate the relationship between IPI and CL shortening.Results: One hundred and eight women with singleton gestations and a qualifying SPTB underwent CL screening. The mean (SD) birth gestational age (GA) of the last pregnancy was 25 (10) weeks, the median IPI was 613 (range 49-6038) days, and the mean (SD) delivery GA in the current pregnancy was 36 (5.3) weeks. Linear regression found no significant relationship between the IPI and the GA of the current birth (p = 0.98). There was a weak significant relationship between IPI and shortest CL (p = 0.04). However, after controlling for the GA of the prior pregnancy, this relationship was non-significant (p = 0.13).Conclusions: IPI does not predict next birth outcome or next-pregnancy mid-trimester CL in high-risk women managed with progesterone and ultrasound-indicated cerclage.