Analysis of the risk factors associated with the severe complications in these patients
We next analyzed the risk factors associated with these severe outcomes using binary non-conditional logistic regression analysis with single factor. Eight factors potentially associated with the consequence of hysterectomy (p<0.05), including placenta implantation detected by ultrasound and/or MRI, placenta previa type, application of vascular occlusion and type of vascular blocking, postpartum hemorrhage (≥1000ml), bleeding volume during the delivery, and confirmed placenta implantation by the surgery. These factors were further analyzed by the non-conditional binary logistic regression with multi-factors. As shown in Table S1, 5.319 times higher potential of hysterectomy was found in the patients with uterine artery embolization than those with abdominal aortic balloon occlusion. This probability was almost doubled (1.002 times) with every 1ml increase of bleeding during the delivery, relevant to that before bleeding. It suggested that the mode of vascular embolization and the volume of hemorrhage during delivery were the main risk factors associated with hysterectomy.
Similarly, 7 factors were identified by single factor analysis, which were associated with severe bleeding during the delivery, as shown in Table 1. Evaluation of these risks by multifactor regression analysis showed that the pregnancies with ≥2 cesarean deliveries had higher possibility (3.562 times) of severe bleeding than those with only once. Compared to women without placenta implantation, patients diagnosed or suspected placenta implantation by ultrasound had higher potential (1.631 times, 95% CI:1.000-2.658 or 1.794 times, 95% CI:1.110-2.899) of severe bleeding. Particularly, this probability increased 6.839 and 1.964 times in the pregnancy with confirmed or suspected placenta implantation by surgery than those without implantation (95% CI:4.508-10.377 or 1.259-3.064), respectively. Complete placenta previa also resulted in 1.814 times severe bleeding in patients than marginal one (95% CI:1.219-2.698). These results suggested that cesarean numbers, ultrasound-detected or surgery-confirmed placenta implantation, and type of placenta previa were associated tightly with massive bleeding during the delivery.
Our analysis also demonstrated that under ultrasound every 0.1cm increase of the thickness of uterine scar, promoted the likelihood of placenta implantation to 1.559 times (95% CI:1.205-2.017). Suspected placenta implantation under ultrasound than normal placenta had 7.79 times high likelihood of implantation confirmed later by surgery (95% CI:1.526-39.765). The subjects without MRI examination also had 3.565 times higher probability of placenta implantation than those with non-implantation diagnosed by MRI (95% CI:1.622-7.837). A higher potential of placenta implantation (3.704 times) was also observed in the women with complete placenta previa than marginal one (95% CI:1.699-8.076). These evidences indicated that ultrasound-detected thickness of uterus scar, ultrasound and/or MRI-detected or suspected implantation of placenta, and complete placenta previa, were closely associated with placenta implantation.