Background: A Rapid Response System (RRS) triggered by a single parameter has been introduced in our hospital. Although the criteria were designed for non-obstetric patients, the RRS concept can be applied to obstetric care. Objective: This study aimed to assess the trigger criteria of RRS compared with the modified early obstetric warning system (MEOWS) criteria as a screening tool for obstetric morbidity. Method: We retrospectively reviewed the medical records of women admitted to the maternal and fetal ICU of Kitasato University Hospital in 2015. Based on recorded physiological parameters, all cases were investigated on whether they met the trigger criteria of the Kitasato RRS (KRRS) and MEOWS. Additionally, the obstetric morbidity defined in this study of each case was determined. The diagnostic sensitivity and specificity of KRRS and MEOWS for obstetric morbidity were evaluated. Results: During the study period, 67 of 373 patients met the criteria for obstetric morbidity. The KRRS criteria for diagnosing obstetric morbidity were 51% sensitive and 74% specific, and the MEOWS criteria were 83% sensitive and 79% specific. Of the 33 patients with morbidity but who did not meet the KRRS criteria, 32 were diagnosed with hypertensive disorders of pregnancy. Of 80 patients with no morbidity, but triggered the KRRS criteria, 32 had tachycardia due to ritodrine. Discussion: The sensitivity of the KRRS trigger criteria was lower than that of the MEOWS criteria; this could be attributed to the inability of the KRRS trigger criteria to detect obstetric-specific conditions. KRRS was triggered in cases with non-morbid conditions suggesting that KRRS will not adapt to the physiological changes in obstetric patients. Conclusion: The KRRS criteria have low sensitivity to obstetric morbidity. If KRRS is introduced to an obstetric ward, informing RRS members about the specific conditions of the obstetric patients will be imperative.