To evaluate a universal transvaginal ultrasonogram cervical length screening program on the incidence of a cervical length 20 mm or less and adherence to the management protocol for a cervical length less than 25 mm. We conducted a prospective cohort study of women with singleton gestations 18 0/7 to 23 6/7 weeks of gestation eligible for universal transvaginal ultrasonogram cervical length screening over an 18-month period. Only women receiving antenatal care at our institution were included. Women with a prior spontaneous preterm birth and without delivery data available were excluded. A transvaginal ultrasonogram cervical length of less than 25 mm was managed according to a predetermined protocol. Primary outcomes were the incidence of a cervical length 20 mm or less and adherence to the management protocol for a cervical length less than 25 mm. Secondary outcomes were the incidences of spontaneous preterm birth at less than 37, less than 34, or less than 32 weeks of gestation among women undergoing transvaginal ultrasonogram cervical length screening compared with those not screened. One thousand five hundred sixty-nine of 2,171 (72.3%) eligible women underwent transvaginal ultrasonogram cervical length screening. Overall, 17 (1.1%, 95% confidence interval [CI] 0.66–1.74) women had a cervical length 20 mm or less before 24 weeks of gestation. Management protocol deviations occurred in nine women with a cervical length less than 25 mm (43%, 95% CI 24.3–63.5). There was no difference in the incidence of spontaneous preterm birth at less than 37 weeks of gestation (4.1 compared with 4.7%, adjusted odds ratio [OR] 0.91, 95% CI 0.57–1.45), less than 34 weeks of gestation (1.5 compared with 1.3%, adjusted OR 1.19, 95% CI 0.52–2.74), or less than 32 weeks of gestation (0.8 compared with 0.8%, adjusted OR 0.0.76, 95% CI 0.26–2.25) among women receiving transvaginal ultrasonogram cervical length screening compared with those not screened. In a universal transvaginal ultrasonogram cervical length screening program, the incidence of a cervical length 20 mm or less was 1.1% in women with singleton gestations without prior spontaneous preterm birth. Protocol deviations occurred in 43% of women with a cervical length less than 25 mm. The incidence of spontaneous preterm birth was similar among women undergoing transvaginal cervical length screening compared with those not screened. II