Abstract： Objective:To explore the risk factors of postpartum hemorrhage in parturients undergoing vaginal delivery with a second child and establish a risk prediction model.Methods:Using the convenient sampling method, a total of 2 500 parturients undergoing vaginal delivery with a second child who underwent regular prenatal examinations at Peking University Third Hospital from July 2019 to March 2023 were selected as the research objects. According to the amount of blood loss, parturients with blood loss greater than or equal to 500 ml within 24 hours after delivery were selected as the case group ( n=278), while parturients with blood loss less than 500 ml within 24 hours after delivery in the same period were selected as the control group ( n=2 222). Univariate analysis and binomial Logistic regression were used to analyze the influencing factors of postpartum hemorrhage in parturients with vaginal delivery with a second child. Based on the selected risk factors, a nomogram prediction model was established using R software, and the consistency of the model was tested. Results:The incidence of postpartum hemorrhage in 2 500 parturients undergoing vaginal delivery with a second child was 11.12% (278/2 500). Binomial Logistic regression analysis showed that in in vitro fertilization-embryo transfer, pre-delivery body mass index, lateral perineal incision, neonatal weight, placenta previa, placenta implantation and manual extraction of placenta were the influencing factors for postpartum hemorrhage in parturients undergoing vaginal delivery with a second child ( P<0.05). According to the influencing factors, a nomogram model was established to predict the probability of postpartum hemorrhage in women who gave birth to a second child. The C- index of the prediction model was 0.706, the area under the receiver operating characteristic curve was 0.706, and the χ 2 value of the Hosmer-Lemeshow goodness-of-fit test was 7.720 ( P=0.461) . Conclusions:In vitro fertilization embryo transfer, pre-delivery body mass index, perineal lateral resection, neonatal weight, placenta previa, placental implantation and manual extraction of placenta are risk factors for postpartum hemorrhage in parturients undergoing vaginal delivery for a second child. The prediction model constructed based on risk factors has certain accuracy and clinical value for predicting postpartum hemorrhage in parturients with vaginal delivery of a second child.