Abstract： Objective To investigate the effect of clinical risk factors including maternal underlying medical conditions on the development of preeclampsia (PE) in order to improve and strengthen the early assessment of high clinical risk population of PE.Methods Clinical.observational data of patients with PE in Peking University Third Hospital from November 2008 to January 2011 were analyzed.Comparative analysis was made among medical conditions with PE (M-PE) sub-group and isolated PE (I-PE) sub-group and non-PE pregnancy with or without medical conditions (control group).Results Totally 159 cases,43.09％ (159/369) of total cases of PE had high clinical risk factors (multiple pregnancy and medical conditions) and 32.3％ (97/300) of singleton PE accompanied with medical conditions.The incidence of PE in singleton pregnancies with medical conditions was significantly higher than those without medical conditions [ 15.0％ (97/646) versus 4.45％ (210/4719),P ＜ 0.05 ].In M-PE sub-group,the average age [ ( 31.7 ± 4.5 ) versus ( 29.3 ± 5.2) year-old] and body mass index (BMI) in first trimester [ (26.0 ±5.6) versus (23.3 ± 3.7) kg/m2],the proportion with previous preeclampsia [ 11％ (11/97) versus 4.9％ (10/203) ] and pregnancy loss in third trimester [ 11％ ( 11/97 ) versus 3.0％ ( 6/203 ) ],were higher than those of I-PE sub-group ( all P ＜ 0.05 ).The onset of preeclampsia in M-PE sub-group was earlier than I-PE ( 32.9 versus 34.4 gestation weeks,P ＜ 0.05 ).The proportion serious cases of PE occurring before 32 gestational weeks were higher in M-PE than that of I-PE sub-group [ 45％ (44/97)versus 34.0％ (69/203),P ＜0.05].Multivariate regression analysis showed that previous history of late pregnancy loss and irregular prenatal care were clinical risk factors for early-onset PE whether early-onset was defined as ＜ 34 or ＜ 32 gestational weeks respectively (all P ＜ 0.05) ; medical conditions were risk factors for PE if early-onset was defined as ＜ 32 gestational weeks ( OR =1.718,95％ CI:1.005 - 2.937,P =0.048).Conclusions Multiple pregnancies and pregnancies with medical conditions exceed one-third of total subjects of PE.The onset of PE in subjects with maternal underlying medical conditions was earlier which is the subgroup should not be ignored.The difference of early pregnancy BMI may show the maternal heterogeneity in early onset and late onset of preeclampsia.Assessment of clinical risk factors including the underlying medical disorders for preeclampsia in early trimester should be strengthened.