Bariatric surgery may be associated with subsequent preterm birth; however healthy women are often used as the control group. The aims of this study were to describe preterm birth rates in women who have undergone bariatric surgery compared to an elevated body mass index (BMI) control group; assess whether bariatric surgery is associated with short cervical length; and to assess whether short cervical length predicts preterm birth in women with a history of bariatric surgery. A retrospective cohort study was conducted at an Australian tertiary centre. Singleton births between 2019-2024, for women who had undergone bariatric surgery (bariatric surgery group) and those with a BMI≥35 without a history of bariatric surgery (elevated BMI control group), were included. Baseline characteristics, gestational age and shortest cervical length between 16-24 weeks’ gestation were recorded. Preterm birth was defined as <37 weeks’ gestation, and short cervix was defined as ≤2.5cm. Rates and relative risk of preterm birth and short cervix were determined. There were 329 pregnancies in the bariatric surgery group and 2551 in the elevated BMI control group. There was no significant increase in preterm birth risk with bariatric surgery (RR1.0, 95% CI 0.7-1.4). There was an increased risk of short cervix in the bariatric surgery group (RR 3.1, 95% CI 1.6-6.0), however this was not significantly predictive of preterm birth in the bariatric surgery group (RR 1.8, 95% CI 0.5-7.8). Bariatric surgery does not increase preterm birth risk, when compared to an elevated BMI control group.