The numbers and ratesa of PH according to each risk factor and their trends during the study period.

PH, peripartum hysterectomy.p-values were evaluated by multivariate logistic regression analysis.aRates were calculated per 1,000 deliveries with each risk factor.PH即围产期子宫切除术（peripartum hysterectomy）。采用多因素logistic回归分析评估P值。注a：针对每种危险因素，按每1000例存在该危险因素的分娩病例计算其发生率。