- The study was aimed to assess the impact of obstetric risk factors for preterm delivery among women with MacDonald cerclage performed due to cervical incompetence. A cohort study was conducted including all patients with MacDonald cerclage performed at 12-14 weeks gestation due to cervical incompetence (n = 793). Deliveries occurred between the years 1988 and 2002 in a University Medical Center. A multiple linear regression model was used to assess the impact of maternal characteristics as well as pregnancy complications on the length of pregnancy. The following factors were found to be associated with preterm delivery among these patients, in the univariate analysis: nulliparity, fertility treatments, severe preeclampsia, second-trimester bleeding, premature rupture of membranes (PROM), chorioamnionitis and placental abruption. Using a multiple linear regression model, with backward elimination, the impact of these variables on the length of pregnancy was assessed (R(2) = 0.33, p < 0.001). The mean gestational age at birth among patients without risk factors was 38.1. Second-trimester bleeding reduced gestational age by 6.4 weeks, chorioamnionitis by 5.6 weeks, placental abruption by 5.1 weeks, PROM by 3.2 weeks and severe preeclampsia by 2.4 weeks. Second-trimester bleeding, chorioamnionitis, placental abruption, PROM and severe preeclampsia are ominous signs for preterm delivery among patients with MacDonald cerclage performed due to cervical incompetence.