Contribution of hypertension to severe maternal morbidity.

Background: Maternal mortality and severe maternal morbidity are growing public health concerns in the United States. The Centers for Disease Control and Prevention Severe Maternal Morbidity measure provides insight into processes underlying maternal mortality and may highlight modifiable risk factors for adverse maternal health outcomes.

Objective: The primary objective of this study was to evaluate the association between hypertensive disorders and severe maternal morbidity at a regional perinatal referral center. We hypothesized that women with preeclampsia with severe features would have a higher rate of severe maternal morbidity compared to normotensive women. We also assessed the proportion of severe maternal morbidity diagnoses that were present on admission, in contrast to those arising during the delivery hospitalization.

Study Design: In this retrospective cross-sectional analysis, we assessed rates of severe maternal morbidity diagnoses (eg, renal insufficiency, shock, and sepsis) and procedures (eg, transfusion and hysterectomy) for all 7025 women who delivered at the University of Washington Medical Center from Oct. 1, 2013, through May 31, 2017. Severe maternal morbidity was determined from prespecified International Classification of Diseases diagnosis and procedure codes; all diagnoses were confirmed by chart review. Present-on-admission rates were calculated for each diagnosis through hospital administrative data provided by the Vizient University Health System Consortium. Maternal demographic and clinical characteristics were compared for women with and without severe maternal morbidity. The χ and Fisher exact tests were used to determine statistical significance. Odds ratios and 95% confidence intervals were calculated for the associations between maternal demographic and clinical characteristics and severe maternal morbidity.

Results: Of 7025 deliveries, 284 (4%) had severe maternal morbidity; 154 had transfusion only, 27 had other procedures, and 103 women had 149 severe maternal morbidity diagnoses (26 women had multiple diagnoses). Severe preeclampsia occurred in 438 deliveries (6.2%). Notably, hypertension was associated with severe maternal morbidity in a dose-dependent fashion, with the strongest association observed for preeclampsia with severe features (odds ratio, 5.4; 95% confidence interval, 3.9-7.3). Severe maternal morbidity was also significantly associated with preeclampsia without severe features, chronic hypertension, preterm delivery, pregestational diabetes, and multiple gestation. Among women with severe maternal morbidity, over one third of preterm births were associated with maternal hypertension. American Indian/Alaskan Native women had significantly higher severe maternal morbidity rates compared to other racial/ethnic groups (11.7% vs 3.9% for Whites, P < .01). Overall, 39.6% of severe maternal morbidity diagnoses were present on admission.

Conclusion: Hypertensive disorders in pregnancy are strongly associated with severe maternal morbidity in a dose-dependent relationship, suggesting that strategies to address rising maternal morbidity rates should include early recognition and management of hypertension. Prevention strategies focused on hypertension might also impact medically indicated preterm deliveries. The finding of increased severe maternal morbidity among American Indian/Alaskan Native women, a disadvantaged population in Washington State, underscores the role that socioeconomic factors may play in adverse maternal health outcomes. As 39% of severe maternal morbidity diagnoses were present on admission, this measure should be risk-adjusted if used as a quality metric for comparison between hospitals.