To compare the clinical characteristics of critically ill pregnant women admitted to the intensive care unit (ICU) with different admission methods, in order to make more effective and rational use of ICU resources. A retrospective study was conducted. The clinical data of critically ill pregnant women admitted to ICU of Peking University Third Hospital from January 2006 to July 2019 were analyzed. According to the admission mode to ICU, the pregnant women were divided into emergency admission group (transferred to ICU on the same day or the next day due to critical illness) and planned admission group (transferred to ICU 2 days after admitting in obstetric ward). The clinical characteristics of ICU critical pregnant women, such as the incidence, causes of admission, severity of the disease, main treatment measures, mortality, and medical expenses were collected, and a comparative analysis between the two groups was performed. During the nearly 14 years, a total of 576 critical pregnant women in ICU were enrolled, accounting for 0.8% (576/71 790) of the total number of obstetric inpatients and 4.6% (576/12 412) of the total number of ICU inpatients. Seven maternal deaths accounted for 1.2% of all critically pregnant women transferred to ICU, and the overall mortality of pregnant women was 10/100 thousand. Of the 576 critically pregnant women, there were 327 patients (56.8%) in the emergency admission group and 249 patients (43.2%) in the planned admission group. Compared with the planned admission group, the proportion of elective cesarean section in the emergency admission group was significantly lower (17.7% vs. 94.0%, P < 0.01), and the proportion of emergency cesarean section was significantly higher (65.1% vs. 2.4%, P < 0.01), the acute physiology and chronic health evaluation (APACHE II, APACHE III) scores, simplified acute physiology score II (SAPS II) and Marshall score were significantly higher [APACHE II score: 6.0 (4.0, 9.8) vs. 4.0 (3.0, 7.0), APACHE III score: 14.0 (11.0, 20.3) vs. 12.0 (9.0, 16.0), SAPS II score: 8 (0, 12) vs. 3 (0, 8), Marshall score: 2 (1, 4) vs. 1 (1, 3), all P < 0.01]. The length of ICU stay in the emergency admission group was significantly longer than that in the planned admission group [days: 2 (1, 5) vs. 2 (1, 3), P < 0.01], and the total length of hospital stay was significantly shorter [days: 9 (7, 13) vs. 13 (10, 18), P < 0.01]. Both in the emergency admission group and the planned admission group, obstetric factors were the main reason for admission, 60.9% (199/327) and 70.3% (175/249), respectively. The proportion of postpartum hemorrhage was the highest [35.2% (115/327) and 57.0% (142/249)], followed by preeclampsia/eclampsia [7.0% (23/327) and 7.6% (19/249)]. Only 7 of the 19 critically pregnant women with puerperal infection were planned admission. All 21 patients with acute fatty liver of pregnancy (AFLP) during pregnancy were emergency admission. Among the emergency and planned admission patients, 73 patients (22.3%) and 42 patients (16.9%) required mechanical ventilation (duration of mechanical ventilation > 24 hours), 99 patients (30.3%) and 35 patients (14.1%) needed vasoactive agents, 67 patients (20.5%) and 20 patients (8.0%) received hemodynamic monitoring, and 123 patients (37.6%) and 154 patients (61.8%) were given anticoagulation therapy, respectively. In terms of severity score of critical pregnant women, there were significant differences in APACHE II, APACHE III, SAPS II and Marshall scores of pregnant women with different diseases. Among them, the APACHE III, SAPS II and Marshall scores of AFLP were the highest [21.0 (15.0, 32.5), 12.0 (6.0, 16.5) and 6.0 (3.5, 8.0), respectively]. The APACHE II and APACHE III scores of postpartum hemorrhage were the lowest [4.0 (3.0, 7.0), 12.0 (10.0, 16.0)]. The SAPS II score of pneumonia was the lowest [2.0 (0, 14.0)]. The Marshall score for puerperal infection was the lowest [1.0 (0, 3.0)]. In terms of the total medical expenses, the cost in the emergency admission group was significantly lower than that in the planned admission group [10 thousand Yuan: 3.1 (2.0, 4.7) vs. 4.1 (2.9, 5.8), P < 0.05]. Compared with the critically ill pregnant women who planned to be admitted to ICU, the patients emergency admitted to ICU were more complicated and urgent, and the severity of the condition was scored higher. At present, the severity scoring system commonly used in ICU can only partly evaluate the severity of critically ill pregnant women, therefore, it is necessary to design the specific severity scoring system for critically ill pregnant women to effectively and rationally use the precious ICU resources.