[Analysis of perinatal outcomes in pregnant women with the resolution of placenta previa in the second trimester].

<b>Objective:</b> To investigate perinatal outcomes of pregnant women with the resolution of placenta previa in the second trimester. <b>Methods:</b> This study was a retrospective cohort study, which included singleton pregnant women who received prenatal care and delivered at Peking University Third Hospital from January 1st 2019 to December 31st 2020. A total of 403 pregnant women diagnosed with placenta previa by ultrasound at 20-24 weeks of gestation and the placental position returned to normal before delivery were included in the study group, and 403 pregnant women with normal placental position matched 1∶1 were the control group. The primary outcome was postpartum hemorrhage rate, and secondary outcomes included postpartum bleeding volume, severe hemorrhage complications, blood transfusion, drug application, the application of instrument or surgical hemostasis measures, gestational week of delivery, and neonatal outcomes. The perinatal outcomes were analyzed by univariate and multivariate logistic regression methods. <b>Results:</b> (1) Compared with the control group, the incidence of postpartum hemorrhage [10.4% (42/403) vs 17.6% (71/403)], postpartum hemorrhage volume (median: 375 vs 400 ml), the proportion of postpartum hemorrhage≥500 ml [18.6% (75/403) vs 30.5% (123/403)], and the proportion of application of instrument or surgical hemostasis measures [1.7% (7/403) vs 4.5% (18/403)] in the study group were increased, and the differences were statistically significant (all <i>P</i><0.05). Neonatal outcomes, including birth weight, small for gestational age, hospitalization in neonatal intensive care unit and incidence of neonatal asphyxia, were compared between the two groups, and there were no statistically significant differences (all <i>P</i>>0.05). (2) In pregnant women with vaginal delivery, the postpartum hemorrhage rate [31.7% (66/208) vs 17.5% (39/223)], postpartum hemorrhage volume (median: 390 vs 380 ml), the proportion of instrument or surgical hemostasis measures [3.8% (8/208) vs 0.4% (1/223)] of the study group were higher than those of the control group, and the differences were statistically significant (all <i>P</i><0.05). There was no significant difference in the rate of postpartum hemorrhage between the study group and the control group who gave birth by cesarean setion (<i>P</i>=0.545), but the proportion of postpartum hemorrhage≥500 ml in the study group and the control group were 29.2% (57/195) and 20.0% (36/180), and the difference was statistically significant (<i>P</i>=0.039). (3) The results of multivariate analysis showed that compared with the control group, the risk of postpartum hemorrhage (a<i>OR</i>=2.042, 95%<i>CI</i>: 1.313-3.175), the application of drugs (a<i>OR</i>=1.684, 95%<i>CI</i>: 1.142-2.484) and the application of instruments or surgical hemostasis measures (a<i>OR</i>=2.696, 95%<i>CI</i>: 1.089-6.675) were significantly increased in the study group (all <i>P</i><0.05). Among women who delivered vaginally, the risk of postpartum hemorrhage in the study group was 2.021 times greater than that in the control group (95%<i>CI</i>: 1.269-3.220; <i>P</i>=0.003). <b>Conclusion:</b> In women with placental previa in the second trimester of pregnancy, even if the placental position returns to normal before delivery, it is still a high risk factor for postpartum hemorrhage, especially in vaginal delivery.