Placental height, together with the distance from the short side of the placental edge to the internal cervical os, provides an accurate assessment of bleeding risk for placenta previa

Aim: Among the most serious complications of placenta previa is bleeding during cesarean delivery. We developed a method of predicting bleeding risk using predelivery MRI or ultrasonography and discuss our findings.Methods: We conducted a retrospective cohort study of cesarean deliveries involving placenta previa between January 2014 and March 2020. We assessed ultrasonography and MRI measurements of the distance from the short side of the placental edge to the internal cervical os (PI) and assessed MRI measurements of placental height (PH). We then analyzed the relation between blood loss and each of these measurements.Results: Of 57 qualifying deliveries, total previa was present in 38 patients (66.7%), and marginal or partial previa in 19 (33.3%). Median blood loss was 1,510 ml (interquartile range, 1,170–2,000 ml). PI distance was positively correlated with blood loss; measurements at 30 to 32 gestational weeks were more correlated than at 35 to 37 gestational weeks by ultrasonography. Moreover, MRI measurements at 33 to 34 gestational weeks were much more correlated than ultrasonography. There was also a positive correlation for PH.Conclusion: Measurements of PI and PH, particularly measured by MRI at 33 to 34 gestational weeks, are useful predictors of bleeding risk for patients with placenta previa.