Introduction

Rates of maternal mortality and severe maternal morbidity (SMM) are increasing in the United States [1,2]. One approach to reduce adverse outcomes is regionalization of care, the goal of which is to improve outcomes by directing patients to hospitals with optimal capabilities for a given condition [3]. Levels of care, a fundamental aspect of regionalization, are a hospital-level characteristic that describe the intensity of care and hospital risk-based services available. The American College of Obstetricians and Gynecologists (ACOG)/Society for Maternal-Fetal Medicine (SMFM) first published maternal levels of care in 2015 and updated them in 2019 [4,5]. These levels, which are based on expert opinion, describe level I care as basic care and level IV care as regionalized, subspecialty care [4,5]. While maternal levels of care parallel neonatal levels of care and studies have consistently shown that high risk infants have better outcomes in hospitals with higher-level care, evidence demonstrating benefits of high level maternal care and obstetric outcomes is variable [6–10].

Although more than 40% of high-risk obstetric patients do not give birth in a hospital with higher level (III or IV) maternal care, published studies have not consistently identified patients for which higher level care is associated with better outcomes [7,8,10–12]. Most studies utilize hospital-reported maternal levels of care, yet data show that there are often discrepancies and over-reporting of hospital capabilities [7,8,13]. Leveraging administrative data to determine the empiric level of care based on the patients birth hospitals are providing care for offers a unique opportunity to understand the relationship between maternal levels of care and obstetric outcomes [14]. Thus, our objective was to examine if the birth hospital maternal level of care, assessed empirically, is associated with SMM during the birth hospitalization. Given the expectation that all birth hospitals should be prepared to manage common, treatable complications that arise during childbirth, a dedicated analysis of obstetric patients with hemorrhage or infection was completed with the associated hypothesis that outcomes for these patients would be similar across all levels of care.

Methods

Results

Of 3,296,520 obstetric patients, 13.8% gave birth in a hospital with level I care, 32.6% with level II care, 9.1% with level III care, and 44.5% with level IV care. Table 1 shows patient characteristics by level of care. There were 245,604 (7.5%) patients identified with infection or hemorrhage during the birth hospitalization (patient characteristics in S3 Table). Hospitals with higher level maternal care were often non-profit, teaching hospitals, with higher annual birth volume (Table 1).

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Table 1. Patient-level Characteristics by Maternal Level of Care (N = 3,296,520).

https://doi.org/10.1371/journal.pone.0353016.t001

Among all obstetric patients, the proportion of patients with SMM increased with increasing level of care; level I: 2,160 (0.47%), level II: 5,965 (0.56%), level III: 2,211 (0.74%), and level IV: 13,836 (0.94%) (Table 1). Similarly, the unadjusted models examining the association of level of care (reference level IV) with SMM found a lower risk ratio (RR) of SMM in levels I, II, and III (Fig 1). In multivariable analysis, this association remained significant only for hospitals with level I care (adjusted risk ratio [aRR] 0.87, 95% confidence interval [CI] 0.76, 0.999) (Fig 1, full model output in S1 File). The sensitivity analysis examining associations during the pre-guideline (2010–2015) and post-guideline (2016–2020) epochs among all obstetric patients found no associations between maternal level of care and SMM in the pre-guideline epoch (level I aRR 0.91, 95% CI 0.77, 1.07; level II aRR 0.99, 95% CI 0.86, 1.13; level III aRR 1.13, 95% CI 0.91, 1.40; level IV reference). In the post-guideline epoch there was a lower aRR of SMM in hospitals with level I and level II maternal care among all obstetric patients (level I aRR 0.83, 95% CI 0.71, 0.97; level II aRR 0.84, 95% CI 0.74, 0.95; level III aRR 0.87, 95% CI 0.74, 1.02; level IV reference).

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Fig 1. Unadjusted and Adjusted Risk Ratios of SMM by Maternal Level of Care for All Obstetric Patients (left panel) and Patients with Treatable Childbirth Complications (right panel).

Figure footnote: Model covariates include birth parent age, race and ethnicity, birth parent education, birth parent insurance type, obstetric comorbidity score, parity, birth hospital location, state, and year. Abbreviation: SMM – Severe Maternal Morbidity, RR – Risk Ratio.

https://doi.org/10.1371/journal.pone.0353016.g001

Among patients with a treatable childbirth complication the SMM pattern was consistent (level I: 634 [2.3%], level II: 1,671 [2.5%], level III 650 [3.4%], and level IV 4,780 [3.6%] (S3 Table). Yet, in this sub-population, the aRR of SMM was increased in hospitals with level III care (aRR 1.21, 95% CI 1.04, 1.40, reference level IV) (Fig 1, full model output in S2 File). When stratifying by complication, the adjusted models examining patients with infection showed a significant association between level II care and a decreased risk ratio of SMM (aRR 0.85, 95% CI 0.74, 0.97; Table 2, full model output in S3 File). Whereas among patients with hemorrhage, the risk ratio of SMM was significantly increased for both level II and level III care, 1.17 and 1.24 times higher respectively than births in hospitals with level IV care (Table 2, full model output in S4 File).

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Table 2. Unadjusted and Adjusted Risk Ratios of SMM by Maternal Level of Care Stratified by Common Treatable Childbirth Complication.

https://doi.org/10.1371/journal.pone.0353016.t002

In the secondary analysis examining the outcome of SMM including blood product transfusion we found no associations of maternal levels of care with this outcome in the adjusted models including all obstetric patients (S4 Table). Among those with common treatable childbirth conditions, we found a higher aRR of SMM including blood product transfusion in hospitals with level I maternal care (S4 Table). This finding reflects the higher aRR among the subset of obstetric patients who experienced hemorrhage (level I aRR 1.34, 95% 1.10, 1.64; reference level IV) and was noted to a lesser degree in hospitals with level II maternal care (aRR 1.18, 95% CI 1.002, 1.40; reference level IV) (S4 Table).

The secondary analysis stratified by state, which examined the primary outcome (SMM without blood product transfusion), are shown are point estimate ranges in S5 Table. Though point estimates varied across states, patterns generally mirror the primary findings with point estimates <1 among all obstetric patients in hospitals with level I care (reference level IV) and point estimates >1 among obstetric patients with common treatable childbirth conditions, both infection and hemorrhage, in hospitals with level III care (reference level IV).

Discussion

In this four-state cohort, the aRR of SMM for all obstetric patients was lower in birth hospitals with level I care, compared to level IV care. When examining patients with common, treatable childbirth complications that should be appropriately managed by all birth hospitals regardless of level of care, the risk ratio of SMM was higher in level III hospitals, contrary to our hypothesis that rates would be similar. These associations may suggest differences in hospitals and how hospitals approach and facilitate risk-appropriate care during childbirth, with respect to screening, triage, transfer, and their own capabilities.

In this study, obstetric patients who gave birth in hospitals with level I care, which is intended to provide care to lower risk patients and to effectively detect, stabilize, and initiate appropriate intervention when unexpected problems occur [5], had a lower risk of SMM. While this finding was present in the cohort as a whole, it was more prominent (lower point estimates and a similar finding in hospitals with level II maternal care) in the post-guideline epoch. Many obstetric patients are lower-risk, and these associations support risk-appropriate care for this population. Even among the lowest-risk patients complications that require non-routine care still arise [28], and in our data 0.47% of births in level I hospitals developed a SMM. A plausible hypothesis may be that after publication of the 2015 level of care guidelines hospitals with lower level care thought more about their resources and potential limitations and augmented approaches to screening, triage, and transport of obstetric patients at higher risk of complications. Obstetric patient referral and transport peri-delivery is complicated by a variety of factors that could be contributing to findings, including birth hospital choice, self-referral, in-office referral, transfer by personal car (vs ambulance), and hospital-to-hospital intrapartum transport networks, only the latter of which is captured in administrative data. While some characteristics of hospitals with level I care and surrounding systems may be unmeasured, they appear to be facilitating risk-appropriate care for low-risk obstetric patients over time [29].

Conversely, among patients who developed a common complication during childbirth the rate of SMM was highest in hospitals with level III care, which provide subspecialty care and have consistent access to obstetricians, intensive care units, advanced imaging, and basic interventional radiology services [5]. Hospitals with level III and IV care differ with respect to patient case mix and hospital capabilities (on call versus 24-hour in-hospital subspecialists) and delineating these differences in administrative data is challenging. Our analysis could not account for clinical acuity at admission, timing of intrapartum deterioration, indication for emergency cesarean birth (if indicated), severity of infection or hemorrhage, or transfer dynamics (e.g., a patient became too unstable to transfer to a hospital with level IV care). Interestingly, findings differed when stratified by complication type, for patients with infection, the risk of SMM was lower in level II hospitals, while for those with hemorrhage, the risk of SMM was higher in level II and III hospitals. When considering the secondary analysis of SMM including blood product transfusion, there were no detectable differences between levels of care for patients with infection, while the risk of SMM was significantly higher for patients with hemorrhage in level I and II hospitals. Blood product transfusion is a common treatment for hemorrhage. In hospitals with lower level maternal care where other resources or services to manage hemorrhage may not be available, thresholds to transfuse may be lower than level III or IV hospitals, which could contribute to these findings. Collectively, these findings support further nuanced analysis with respect to patient acuity and ongoing studies of practices surrounding hemorrhage management.

Unlike prior studies of levels of care, which often include dedicated analyses of high-risk obstetric patients [7,10,12], this study focused on common, treatable childbirth complications. While all birth hospitals do not have the same patient case mix and are not expected to have the expertise and resources to care for complex obstetric patients, the ability to quickly recognize and appropriately respond to patients with hemorrhage or infection is fundamental to peripartum care. By definition, lower-level hospitals and their patients differ from higher-level hospitals. For example, level IV hospitals are regional perinatal centers that should be engaging in educational initiatives, outcome review, and quality improvement (QI) initiatives with surrounding lower-level hospitals. Level IV centers may have completed more QI work or implemented robust hemorrhage protocols. Engagement in QI, particularly for postpartum hemorrhage, has been associated with marked improvement in outcomes [30] and partnership to disseminate targeted educational materials and facilitate QI efforts may help mitigate the risk of SMM among patients with common childbirth complications in hospitals with lower level care.

While further evaluation of maternal levels of care and risk-appropriate obstetric care during childbirth are needed, these findings bring attention to this important topic. Considering potential future avenues to optimize risk-appropriate care for obstetric patients in the United States could include standardizing state level of care guidelines, incentivizing and expanding level of care verification programs, which ACOG has made efforts to expand in partnership with The Joint Commission [31,32], and increasing visibility and public reporting of level of care data and associated hospital obstetric capabilities. Systematic changes that optimize risk-appropriate care for obstetric patients may improve outcomes.

Conclusion

In the four states studied, compared to level IV care, we found associations of level I care with lower rates of SMM among all obstetric patients and level III care with higher rates of SMM among patients with common treatable complications during childbirth. While unmeasured differences in patient triage, referral, and transfer patterns may influence associations, these data illustrate the ongoing need to understand and refine approaches to risk-appropriate obstetric care delivery. These findings can inform future studies that evaluate hospital and health system-based efforts to optimize patient risk and hospital capability assessment and operationalize maternal levels of care to ultimately improve patient outcomes.

Supporting information

Acknowledgments

The authors would like to recognize the Michigan Department of Health and Human Services, the Oregon Health Authority Hospital Reporting Program, the Pennsylvania Health Care Cost Containment Council (PHC4), and the South Carolina Revenue and Fiscal Affairs Office, Health and Demographics Section. The PHC4 is an independent state agency responsible for addressing the problem of escalating health costs, ensuring the quality of health care, and increasing access to health care for all citizens regardless of ability to pay. PHC4 has provided data to this entity in an effort to further PHC4’s mission of educating the public and containing health care costs in Pennsylvania. PHC4, its agents, and staff, have made no representation, guarantee, or warranty, express or implied, that the data -- financial, patient, payor, and physician specific information -- provided to this entity, are error free, or that the use of the data will avoid differences of opinion or interpretation. This analysis was completed by the authors, the aforementioned organizations and their staff bear no responsibility or liability for the results of the analysis and the release of the data does not imply endorsement of this study or findings, which are solely the opinions of the authors.