Introduction

Maternal mortality remains a major global concern in obstetric care, with approximately 260,000 women dying each year from causes related to pregnancy and childbirth.1 Although the maternal mortality ratio (MMR) is relatively low in high-income countries (approximately 10 per 100,000 live births), severe maternal morbidity and near-miss events remain substantial patient safety concerns, highlighting the need for early recognition and prompt intervention.1–4

In Japan, the MMR is low by global standards (approximately 4 per 100,000 live births).5 However, as in other high-income countries, the risk of severe maternal morbidity has increased in recent years, driven by several factors, including pre-existing comorbidities,6,7 advanced maternal age,8 and the use of assisted reproductive technologies (ART).9 Pre-existing conditions such as hypertension, kidney disease, and diabetes mellitus can worsen during pregnancy and increase vulnerability to decompensation and organ dysfunction.10–12 Moreover, advanced maternal age and ART are associated with an increased risk of serious maternal complications, including hypertensive disorders of pregnancy, abnormal placentation, and placental abruption.13–18 These conditions may result in massive hemorrhage, circulatory collapse, seizures, and cerebrovascular or cardiovascular events during the peripartum period, potentially leading to rapid and severe maternal deterioration.19,20 Collectively, these trends underscore the growing importance of in-hospital patient safety systems capable of early recognition of clinical deterioration and prompt intervention.

Rapid Response Systems (RRSs) may play a key role in improving patient safety in obstetric care. RRSs are hospital-wide patient safety systems designed to identify clinical deterioration early and provide rapid, team-based intervention to prevent adverse outcomes.21,22 In Japan, RRS was introduced in 2008 and has gradually expanded, with a 2024 nationwide survey reporting that approximately 81% of acute care hospitals had implemented RRS.23,24 Systematic reviews in adult and pediatric populations have shown that RRS implementation reduces in-hospital cardiac arrest and mortality.25 However, evidence regarding RRS in obstetric populations remains limited. Previous single-center studies from Australia and Canada have described obstetric RRS or emergency team activations, including their indications, team responses, and patient outcomes.26,27 A Korean single-center study also reported that medical emergency team implementation may reduce intensive care unit (ICU) admissions among obstetric patients.28 These studies, however, were conducted in specific institutional settings, and multicenter evidence comprehensively describing obstetric RRS activations remains scarce, limiting guidance for effective RRS operation in obstetric care. Furthermore, obstetric patients experience pregnancy-related physiological changes and may develop obstetric-specific conditions. Circulating blood volume and heart rate generally increase during pregnancy, whereas blood pressure tends to decrease in mid-pregnancy and then gradually returns toward pre-pregnancy levels in late pregnancy;29,30 in addition, some patients develop hypertensive disorders of pregnancy. These physiological and disease-related changes may complicate the interpretation of standard RRS activation criteria based on vital signs and may result in activation patterns that differ from those observed in non-obstetric patients. Therefore, characterizing obstetric RRS activations within hospital-wide RRS operations may inform both obstetric RRS practice and overall RRS operations.

This study aimed to examine the characteristics and outcomes of obstetric RRS activations using the In-Hospital Emergency Registry in Japan (IHER-J), a multicenter Japanese registry.23 The analysis focused on patient characteristics, activation patterns, triggers for activation, interventions performed by the RRS team, causes of deterioration, and clinical outcomes among obstetric patients. In addition, we conducted an exploratory analysis comparing activation patterns, triggers, and interventions between obstetric and non-obstetric patients (all other patients in the cohort) to further characterize obstetric RRS activations.

Materials and Methods Study Design, Data Source, and Setting

This retrospective observational study used data from the IHER-J, which is registered with the University Hospital Medical Information Network Clinical Trials Registry (UMIN000012045). The present analysis covered the period from November 2017 to August 2024. As of July 2023, the latest time point when hospital information was available for all participating hospitals, 61 hospitals across Japan (including 20 university hospitals [32.8%]) had been approved to participate in the registry; of these, 59 (96.7%) had an obstetrics and gynecology department. As of August 2024, 52 of the 61 approved hospitals were actively contributing data to the registry. The registry includes demographic, physiological, and clinical data for patients at participating hospitals for whom the RRS was activated. Participating hospitals used similar RRS activation criteria based on respiratory, circulatory, neurological, and other parameters.31 Rapid response team composition was determined by each participating hospital. Participation in the IHER-J and subsequent analyses were approved by the central ethics committee of St. Marianna University School of Medicine (IRB No. 2498 [B30]). The present study was also approved by the Ethics Committees of the Nagoya City University Graduate School of Medical Sciences and Nagoya City University Hospital (IRB No. 60240061). Because all registry data were anonymized, the requirement for individual informed consent was waived. Information regarding the study was publicly available on the institutional website to allow patients to opt out. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments and followed the Strengthening the Reporting of Observational Studies in Epidemiology guidelines.32

Study Population and Definitions

The study population included all patients with RRS activation who were recorded in the IHER-J database from November 2017 to August 2024. Obstetric patients were defined as those who were pregnant or within 1 week postpartum at the time of RRS activation. Patients with insufficient information to determine obstetric status were excluded. All other patients in the cohort were classified as non-obstetric.

Study Variables and Outcomes

Baseline patient characteristics included demographic data (age and sex), hospitalization status, primary diagnosis, postoperative status (defined as RRS activation within 7 days after surgery), and vital signs at the time of RRS activation.

Study variables included the profession initiating RRS activation (physician, nurse, others), time of activation (daytime [08:00–16:59]; nighttime [17:00–07:59]), location of activation (eg hospital ward, outpatient section), triggers for activation (eg desaturation, hypotension, decreased consciousness), interventions performed by the RRS team, and causes of deterioration. Triggers, interventions, and causes of deterioration could be recorded as multiple selections for each case. Triggers for RRS activation were classified into respiratory, circulatory, neurological, and other categories based on clinical presentation and underlying pathophysiology, and are listed in Table S1. Causes of deterioration, as prespecified in the registry, are listed in Supplementary Box 1. Regarding terminology for bleeding-related events, which may vary depending on the context, we used “massive bleeding” to refer to the trigger for RRS activation and “massive hemorrhage” to refer to the underlying cause of deterioration.

Outcomes included patient disposition immediately after RRS activation (eg ICU admission, high-dependency unit [HDU] admission), clinical outcomes at 24 hours, and outcomes at 30 days after activation or at discharge (continued hospitalization, discharge, or death). Neurological outcomes at 30 days or at discharge were evaluated using the Cerebral Performance Category (CPC) score.33

Statistical Analyses

Continuous variables were summarized as medians with interquartile ranges (IQRs), whereas categorical variables were presented as counts and percentages. Exploratory comparisons of activation patterns (profession initiating RRS activation and time and location of activation), triggers for RRS activation, and interventions were conducted between obstetric and non-obstetric patients. The Mann–Whitney U-test was used for continuous variables, and the chi-square test or Fisher’s exact test, as appropriate, was used for categorical variables. All tests were two-sided, and p<0.05 was considered statistically significant. Risk differences (RDs) and 95% confidence intervals (CIs) were calculated using Newcombe’s method (Method 10).34 This was a descriptive study, and comparisons were exploratory; therefore, no adjustment for multiple comparisons was applied. Analyses were conducted on a complete-case basis for each variable; patients with missing data for a given variable were excluded from the analysis of that variable. No imputation of missing data was performed. For patients who experienced multiple RRS activations during the study period, each activation was treated as an independent case. All statistical analyses were performed using Stata/SE 18.0 (StataCorp LLC, College Station, TX, USA).

Results

A total of 16,125 patients with RRS activation were included during the study period. After excluding patients whose obstetric status could not be determined (n=5), 141 obstetric patients (0.9%) and 15,979 non-obstetric patients (99.1%) were identified (Figure 1).

Figure 1 Study flow chart.

Abbreviation: IHER-J, In-Hospital Emergency Registry in Japan.

Baseline Characteristics and Activation Patterns

Demographic and clinical characteristics of obstetric and non-obstetric patients are summarized in Table 1. The median age was 34 years (IQR 31–38) in obstetric patients and 74 years (IQR 61–82) in non-obstetric patients. The proportions of inpatients were 84.4% and 81.8%, respectively. In obstetric patients, the primary diagnosis was obstetric in all cases; concomitant medical and surgical diagnoses were present in 1.4% and 2.8%, respectively. In non-obstetric patients, primary diagnoses were medical (46.7%) and surgical (28.1%). Postoperative patients accounted for 23.4% of obstetric patients and 11.0% of non-obstetric patients.

Table 1 Demographic and Clinical Characteristics of Obstetric and Non-Obstetric Patients with RRS Activation

RRS activation patterns are summarized in Table 2. Regarding the profession initiating RRS activation, the proportion of physician-initiated activations was higher in obstetric than in non-obstetric patients (31.8% vs 18.1%; RD 13.7, 95% CI 6.3 to 22.1; p<0.001), whereas the proportion of nurse-initiated activations was lower (55.3% vs 75.6%; RD −20.3, 95% CI −28.9 to −12.1; p<0.001). The proportion of nighttime activations (17:00–7:59) was higher in obstetric than in non-obstetric patients (47.1% vs 32.9%; RD 14.3, 95% CI 6.2 to 22.6; p<0.001).

Table 2 RRS Activation Patterns in Obstetric and Non-Obstetric Patients: Profession Initiating Activation, Time, and Location

Triggers for RRS Activation

Triggers are summarized in Table 3. Among obstetric patients, the most common triggers were decreased consciousness (34.0%), massive bleeding (31.2%), hypotension (29.8%), and concern about the patient (21.3%). Compared with non-obstetric patients, obstetric patients had higher proportions of activations triggered by massive bleeding (RD 28.8, 95% CI 21.7 to 36.8; p<0.001), hypotension (RD 7.5, 95% CI 0.5 to 15.5; p=0.033), decreased consciousness (RD 8.0, 95% CI 0.7 to 16.2; p=0.031), and seizure (RD 6.1, 95% CI 2.4 to 12.1; p<0.001), whereas activations triggered by desaturation were less frequent (RD −14.1, 95% CI −18.6 to −7.7; p<0.001). In analyses by trigger category (respiratory, circulatory, neurological, and other), obstetric patients had higher proportions of circulatory triggers (51.8% vs 35.3%; RD 16.5, 95% CI 8.3 to 24.6; p<0.001) and neurological triggers (38.3% vs 28.5%; RD 9.7, 95% CI 2.1 to 18.0; p=0.011), whereas respiratory triggers were less common (22.7% vs 40.2%; RD −17.5, 95% CI −23.7 to −9.9; p<0.001).

Table 3 Triggers for RRS Activation in Obstetric and Non-Obstetric Patients

RRS Interventions

RRS interventions are shown in Figure 2 and summarized in Table S2. The proportion of patients receiving any intervention was 74.5% in obstetric patients and 76.3% in non-obstetric patients. In obstetric patients, the most common interventions were diagnostic testing (39.6%), fluid bolus (36.4%), oxygen administration (34.5%), medication (28.3%), and transfusion (20.7%). Fluid bolus (RD 17.2, 95% CI 9.7 to 25.5; p<0.001) and transfusion (RD 17.8, 95% CI 11.9 to 25.2; p<0.001) were more common in obstetric than in non-obstetric patients. In contrast, bag-valve-mask ventilation (RD −5.3, 95% CI −8.2 to −0.2; p=0.044) and suction (RD −10.7, 95% CI −12.5 to −6.4; p<0.001) were less common.

Figure 2 RRS interventions in obstetric and non-obstetric patients. Multiple selections were allowed. *p<0.05, ***p<0.001. “Intervention” indicates any intervention performed by the RRS team.

Abbreviations: BVM, bag-valve-mask ventilation; NPPV, non-invasive positive pressure ventilation.

Causes of Deterioration and Outcomes After RRS Activation in Obstetric Patients

Causes of deterioration in obstetric patients are shown in Figure 3. Massive hemorrhage was the most common cause (39.0%), with infection/sepsis (5.0%), distributive shock (5.0%), cerebrovascular disease (4.3%), and respiratory failure (4.3%). Outcomes after RRS activation in obstetric patients are summarized in Table 4. ICU admission occurred in 29.1% of obstetric patients, and HDU admission in 6.4%. At 30 days after RRS activation or at hospital discharge, no deaths occurred, and CPC scores were 1 in 98.6% of patients; two patients (1.4%) had a CPC score of 2, and none had a CPC score of ≥3.

Table 4 Outcomes in Obstetric Patients with RRS Activation

Figure 3 Causes of deterioration in obstetric patients with RRS activation. Multiple selections were allowed. No cases of myocardial infarction/myocardial ischemia, airway obstruction/sputum plugging, tension pneumothorax, pulmonary embolism, cardiac tamponade, aortic dissection/ruptured aortic aneurysm, metabolic disorder/electrolyte abnormality, hypothermia, poisoning, or trauma were identified.

Abbreviation: RRS, rapid response system.

Discussion

In this multicenter cohort study in Japan, obstetric patients accounted for 0.9% of all RRS activations. Compared with non-obstetric patients, obstetric patients had higher proportions of physician-initiated and nighttime activations. The most common triggers in obstetric patients were decreased consciousness, massive bleeding, and hypotension, with massive hemorrhage (39%) as the leading cause of deterioration. Overall, 74.5% of obstetric patients received at least one intervention. Common interventions included diagnostic testing, oxygen administration, fluid bolus, medication, and transfusion; fluid bolus and transfusion were performed more frequently than in non-obstetric patients. The ICU admission rate among obstetric patients was 29.1%, and no in-hospital deaths occurred.

Relationship to Previous Studies Regarding Triggers and Causes of Deterioration

Previous studies have reported similar findings. An Australian single-center study of an ICU–led rapid response team for obstetric patients identified hypotension, concern about the patient, and decreased consciousness as the most common triggers for activation.26 A Korean single-center study of obstetric patients managed by a medical emergency team reported pulmonary edema and hypovolemic shock as major causes of deterioration, both associated with obstetric hemorrhage and transfusion.28 Consistent with these findings, the present study identified decreased consciousness, hypotension, and massive bleeding as the most common triggers, with massive hemorrhage as the leading cause of deterioration. Moreover, fluid bolus administration and transfusion were performed more frequently in obstetric patients than in non-obstetric patients. These findings suggest that the RRS may facilitate early recognition and intervention, particularly for hemorrhagic complications. Furthermore, given that hemorrhage is the primary cause of ICU admission among obstetric patients in Japan,35 our findings support the clinical relevance of the RRS for this population.

Respiratory triggers for RRS activation were relatively uncommon in obstetric patients. This contrasted with non-obstetric patients, in whom respiratory triggers were a major driver of activation, consistent with an integrative review reporting that respiratory compromise was the most common trigger in adult and pediatric populations.36 This difference likely reflects variation in the underlying causes of deterioration. In obstetric patients, hemorrhage was the most common cause, with infection, distributive shock, and cerebrovascular disease also identified. These conditions commonly present with clinical signs of circulatory failure and/or impaired consciousness,37–39 which may explain the activation profile in which circulatory and neurological triggers were more prominent. However, the Korean study reported pulmonary edema associated with hemorrhage and transfusion as a major cause of deterioration, which may represent secondary respiratory decompensation.28 This discrepancy suggests that differences in RRS operations, including activation criteria and timing, may influence the RRS activation profile in obstetric patients. Based on these findings, obstetric RRS operations may need to emphasize early response and resource mobilization for circulatory failure and/or impaired consciousness, while maintaining readiness for respiratory management.

Profession Initiating RRS Activation in Obstetric Patients

Another notable finding was the higher proportion of physician-initiated RRS activations in obstetric patients compared with non-obstetric patients. Although the reasons cannot be determined directly from this study, several explanations are plausible. Obstetric care requires specialized management of both maternal and fetal conditions, and clinical decision-making may therefore be concentrated among physicians within established hierarchical escalation pathways and interprofessional role boundaries.40,41 Furthermore, intrapartum emergency management typically requires close collaboration between midwives and obstetricians within legal and regulatory frameworks, which may lead to more physician-initiated RRS activations.42,43 While such stepwise escalation of care may allow physicians to assess the appropriateness of interventions based on clinical conditions, delays in activation and subsequent interventions may also worsen patient outcomes in some situations,44 highlighting important considerations for RRS operations in obstetric settings.

Physician-initiated activation may also reflect the complexity of managing severe obstetric complications, including obstetric hemorrhage, cerebrovascular disease, and eclampsia. These conditions often require not only obstetric expertise but also advanced systemic management and close coordination with the operating room and ICU.45,46 Physicians may therefore initiate RRS activation to mobilize additional resources and expertise, which may contribute to the higher proportion of physician-initiated activations in obstetric patients. Given this complexity, obstetric RRS activations may benefit from multidisciplinary collaboration, including clinicians with emergency medicine and critical care expertise who can provide advanced systemic management.

Timing of RRS Activations in Obstetric Patients

In the present study, 47.1% of RRS activations in obstetric patients occurred at nighttime, a higher proportion than in non-obstetric patients. A Canadian study also reported that approximately 67% of obstetric RRS events occurred outside regular working hours,27 consistent with our findings that nighttime activation is a characteristic feature of obstetric RRS. Several factors may explain this pattern. Spontaneous labor often progresses overnight and into the early morning,47–49 potentially increasing the occurrence of acute complications such as hemorrhage and eclampsia during these hours. Additionally, studies have reported an association between nighttime delivery and severe maternal morbidity, suggesting vulnerabilities in staffing, resources, and care processes during these hours.50,51 Together, these clinical and system-level factors may explain the increased nighttime RRS activations observed in obstetric patients. Overall, these findings suggest that, particularly at night when clinical resources may be limited, the RRS may function as a safety net to support timely recognition and response to obstetric deterioration.

Potential Role of RRS in Obstetric Patients

While systematic reviews in adult and pediatric populations have shown that RRS implementation reduces in-hospital cardiac arrest and mortality,25 evidence regarding the effectiveness of RRSs in obstetric patients remains limited. Several studies suggest a potential role for RRSs in obstetric care. In the United States, a single-center study reported that implementing an obstetric-specific rapid response team, including obstetricians, increased activation rates among obstetric patients and improved care processes, suggesting that a dedicated team may better address the unique needs of obstetric emergencies.52 A Korean single-center study reported that a medical emergency team functioning as a hospital-wide rapid response team reduced ICU admissions among obstetric patients, suggesting that even a general RRS may provide clinical benefits in obstetric settings.28

In the present study, interventions were performed in 74.5% of obstetric patients following RRS activation, a proportion comparable to that in non-obstetric patients. Notably, because massive hemorrhage was the most common cause of deterioration, fluid bolus and transfusion were frequently performed, consistent with management directed toward hemorrhagic deterioration. Additionally, 29.1% required ICU admission, with no deaths, indicating that RRS activations may help identify high-acuity patients and escalate care when needed. Although the effectiveness of the RRS could not be evaluated directly, these findings suggest that RRSs may also play a role in obstetric patients, consistent with their established role in other patient populations.

Limitations and Future Research

This study has several limitations. First, the number of obstetric patients in our cohort was small. This may partly reflect the rarity of clinical deterioration requiring RRS activation among obstetric patients, who are generally younger and have fewer comorbidities than the general inpatient population. However, this small number may also reflect incomplete capture of obstetric-specific deterioration events within the registry. The RRS activation criteria used at participating hospitals may not adequately account for vital sign changes associated with pregnancy physiology or those modified by obstetric-specific conditions, such as hypertensive disorders of pregnancy.29,30 In addition, obstetric patients with clinical deterioration may have been triaged and managed directly by obstetricians before escalation to the RRS. Therefore, the present study should be interpreted as describing obstetric cases recorded through RRS activation, rather than all obstetric deterioration events. Nevertheless, to our knowledge, evidence on RRS activation in obstetric patients has been confined to single-center studies, making our multicenter analysis a key strength of this study. Second, because obstetric patients were identified based on the predefined registry category of pregnancy or within 1 week postpartum, deterioration occurring beyond this period could not be captured. Moreover, gestational age and antepartum/postpartum timing were not recorded, limiting our ability to characterize activations by these factors. Third, causes of deterioration were recorded using predefined registry categories; conditions outside these categories were classified as “other,” and detailed obstetric diagnoses such as eclampsia or amniotic fluid embolism were not available. Fourth, the study included hospitals in Japan, and differences in health care systems and sociocultural contexts may limit generalizability to other countries. Fifth, inter-hospital heterogeneity may have influenced our findings. Details of activation criteria, response-team composition, available interventions, and implementation fidelity may have varied across hospitals. In addition, we could not confirm whether each facility maintained a 24-hour RRS. These factors may have influenced the temporal patterns of RRS activations, including the higher proportion of nighttime activations. Therefore, the findings of this study should be interpreted with caution. Finally, each RRS activation was treated as an independent event, and repeat activations in the same individual could not be identified. Future studies should examine the frequency of repeat activations and the characteristics of such cases, which may provide insight into the adequacy of initial management and the trajectory of clinical deterioration.

Despite these limitations, our study provides foundational information on the characteristics and operational patterns of RRS activations among obstetric patients. Future studies should establish a dedicated obstetric RRS registry that captures more granular clinical data, including gestational age, whether activation occurred antepartum or postpartum, and obstetric-specific diagnoses, to further clarify the role of RRSs in obstetric care. In addition, comparative studies are warranted to evaluate the effectiveness of RRSs in obstetric patients and to assess whether obstetric-specific activation criteria and response-team composition are needed to address pregnancy-related physiological changes and obstetric-specific complications.

Conclusion

This multicenter Japanese registry-based study describes the characteristics and outcomes of RRS activations in obstetric patients. Obstetric patients accounted for 0.9% of all RRS activations and had higher proportions of physician-initiated and nighttime activations than non-obstetric patients. Obstetric RRS activations were commonly triggered by decreased consciousness, massive bleeding, and hypotension, with massive hemorrhage as the leading cause of clinical deterioration. Interventions, including diagnostic testing, fluid bolus, oxygen administration, medication, and transfusion, were frequently performed, and 29.1% of obstetric patients required ICU admission. These findings provide insight into obstetric RRS activations and may inform rapid response practices and patient safety approaches in obstetric care.

Institutional Review Board Statement

This study was approved by the Institutional Review Board of Nagoya City University (approval number: 60240061). Because all data were de-identified, the requirement for patient informed consent was waived.

Abbreviations

RRS, rapid response system; ICU, intensive care unit; MMR, maternal mortality ratio; ART, assisted reproductive technology; IHER-J, In-Hospital Emergency Registry in Japan; HDU, high-dependency unit; CPC, Cerebral Performance Category; IQR, interquartile range; RD, risk difference; CI, confidence interval; BVM, bag-valve-mask ventilation; NPPV, non-invasive positive pressure ventilation.

Data Sharing Statement

The data used in this study were provided by the In-Hospital Emergency Committee in Japan under license. The datasets are available from the corresponding author upon reasonable request, with permission from the In-Hospital Emergency Committee in Japan.

Consent for Publication

All data were de-identified; therefore, the requirement for patient informed consent was waived. To ensure that patients had the opportunity to opt out, information about the study was made publicly available on the institutional website (https://nagoya-cu.bvits.com/rinri/publish_document.aspx?ID=1321. Accessed February 15, 2026.).

Acknowledgments

The authors thank the In-Hospital Emergency Committee in Japan for supporting this study and the In-Hospital Emergency Study Group for assistance with data collection. We would like to thank Editage (www.editage.jp) for English language editing.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Funding

This research was supported by the Nagoya Co-Creation Research Fund (approval number: 2024-023).

Disclosure

The authors declare that they have no competing interests.

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