This prospective study was conducted to compare risk factors and pregnancy outcomes between women with complete placenta previa and those with incomplete placenta previa diagnosed in mid-pregnancy.The study was carried out from April 2014 to December 2015,during which 70 patients with complete previa and 113 with incomplete previa between 20+0 weeks and 25+6 weeks of gestation were included.Matal demographics and pregnancy outcomes were compared between the two groups.Comparisons between categorical variables were tested by chi-squared test and those between continuous variables by Student t test.Resolution ofprevia occurred in 87.43％ of the studied women.The mean gestational age at resolution was 32.1±4.4 weeks.Incidence of matal age ≥35 years and incidence of prior uterine operation ＞3 were high in women with complete previa (28.6％vs.8.8％,P=0.003;28.6％ vs.8.8％,P=0.003).Resolution of previa occurred less often in complete previa group (74.3％ vs.95.6％,P=0.001).Women with complete previa admitted earlier (37.3±2.0 weeks vs.38.1±1.4 weeks,P=0.011) and delivered earlier (37.7±1.2weeks vs.38.3±1.4 weeks,P=0.025).Matal age ≥35 years and prior uterine operation ＞3 increase the risk of complete previa in mid-pregnancy.Placenta previa is more likely to persist in women with complete previa than those with incomplete previa diagnosed in midpregnancy.What is more,women with complete previa in mid-pregnancy deliversearlier.