Hypertensive disorders of pregnancy, chronic hypertension, and obesity are driving up rates of severe maternal morbidity in the US, a retrospective cohort study has found.

“These findings highlight the urgent need for preventive interventions targeting cardiometabolic health before, during, and after pregnancy,” said the authors, led by Tetsuya Kawakita, MD, MS, associate professor of obstetrics and gynecology at the Old Dominion University in Norfolk, Virginia.

The study was published recently in Obstetrics & Gynecology.

Severe maternal morbidity refers to any unexpected, life-threatening complication such as eclampsia, acute renal failure, or sepsis, arising during labor and delivery, resulting in either morbidity or death. Between 2008 and 2021, US rates of severe maternal morbidity went from 146.8 to 179.8 per 100,000 delivery hospitalizations, according to a 2023 study.

Kawakita and colleagues studied the period from 2016 to 2022 to estimate what proportion of severe maternal morbidity during that time could be attributed to changing maternal demographic and clinical profiles, including these six risk factors: advanced maternal age, obesity, pregestational diabetes, gestational diabetes, chronic hypertension, and hypertensive disorders of pregnancy.

“Despite a growing body of literature examining individual risk factors, few studies have systematically assessed the extent to which these changing maternal characteristics explain the observed rise in SMM [severe maternal morbidity] at the population level,” the authors wrote.

To that end, Kawakita and his colleagues collected retrospective cohort data from the federal Nationwide Readmissions Database from 2016 to 2022, on over 25 million weighted delivery hospitalizations. To determine severe maternal morbidity as a primary outcome, the investigators applied the CDC’s 21-condition severe maternal morbidity algorithm to nontranfusion outcomes, with transfusion as a secondary outcome to account for the high frequency and limited specificity of transfusion as a marker of severity.

They assessed temporal severe maternal morbidity trends while quantifying changes in how risk factor prevalence contributed to the overall increase in severe maternal morbidity.

Hospitals with fewer than 100 annual deliveries were excluded to improve the stability of estimates for rare maternal outcomes. Kawakita and colleagues also excluded delivery hospitalizations transferred from another facility, to minimize duplicate counting. The study population included hospital delivery admissions for participants aged 11-55 years, according to International Classification of Diseases, 10th Revision (ICD-10), Clinical Modification codes. The year 2016 was the first complete calendar year of data under the ICD-10 codes. For both nontransfusion and transfusion outcomes, in-hospital maternal death was included, in addition to the CDC-defined indicators.

The investigators found that between 2016 and 2022, rates of severe maternal morbidity increased from 1.5% to 2.2%, with nontransfusion severe maternal morbidity rising from 0.7% to 1.0% (P < .001 for both). Among the weighted total of 25,000,955 delivery hospitalizations, 465,859 (1.9%) were complicated by severe maternal morbidity. Nontransfusion deliveries with severe maternal morbidity were 202,102 (0.8%).

The rate of hypertensive disorders of pregnancy rose from 9.8% to 16.6%, chronic hypertension from 1.4% to 2.6%, and obesity from 9.7% to 15.4%. These maternal risk factors were independently associated with higher odds of severe maternal morbidity.

Hypertensive disorders of pregnancy accounted for 32.4% (95% CI, 31.2%-33.7%) of the increase in severe maternal morbidity and 51.3% (95% CI, 48.5%-54.9%) of the increase in nontransfusion severe maternal morbidity. Chronic hypertension and obesity also contributed meaningfully, whereas advanced maternal age (age 35 years or older) and gestational diabetes contributed a smaller portion of the increase.

Gestational diabetes contributed the smallest share of the increase, explaining 0.9% (95% CI, 0.7%-1.1%) of the increase in severe maternal morbidity and 1.5% (95% CI, 1.1%-1.8%) of the increase in nontransfusion severe maternal morbidity.

The prevalence of key maternal risk factors also increased significantly: advanced maternal age went from 16.7% to 20.4%, obesity from 9.7% to 15.4%, pregestational diabetes from 1.1% to 1.6%, gestational diabetes from 7.1% to 9.4%, chronic hypertension from 1.4% to 2.6%, and hypertensive disorders of pregnancy from 9.8% to 16.6% (P < .001 for all). Meanwhile, the proportion of deliveries with prior cesarean delivery did not change significantly (P = .14), and the proportion of multiple gestations declined (from 1.9% to 1.8%, P < .001).

All six maternal risk factors were significantly associated with increased odds of severe maternal morbidity and nontransfusion severe maternal morbidity. Adjusted odds ratios were from 1.11 (95% CI, 1.09-1.13) for gestational diabetes to 3.30 (95% CI, 3.23-3.38) for chronic hypertension for severe maternal morbidity and 1.20 (95% CI, 1.17-1.22) for gestational diabetes to 5.34 (95% CI, 5.20-5.49) for chronic hypertension for nontransfusion severe maternal morbidity.

Those with severe maternal morbidity had government insurance more often than those without severe maternal morbidity. Advanced maternal age, obesity, pregestational diabetes, chronic hypertension, multiple gestation, hypertensive disorders of pregnancy, malpresentation, and prior cesarean delivery were also more prevalent in those with severe maternal morbidity compared with those without. Severe maternal morbidity occurred more frequently at large, metropolitan teaching, and nonfederal government hospitals.

“Our study suggests that the rise in severe maternal morbidity is not explained mainly by maternal age but is more strongly related to increasing cardiometabolic risk, especially hypertensive disorders of pregnancy, chronic hypertension, and obesity,” Kawakita told Medscape Medical News. “In particular, hypertensive disorders of pregnancy were a major contributor to the increase in SMM [severe maternal morbidity] in our analysis. This has implications at both the clinical and public health levels.”

Kawakita also said the study points to the need for a focus on preconception health, chronic disease prevention, and postpartum follow-up.

“At the clinical level, it supports a stronger emphasis on early risk identification, blood pressure surveillance, and timely management of hypertensive disease in pregnancy,” Kawakita said. “It also reinforces the importance of prescribing low-dose aspirin for pregnant patients who are at risk for preeclampsia, as part of evidence-based prevention.”

Immediate past president of the Society for Maternal-Fetal Medicine, and professor of obstetrics and gynecology at the Hospital of the University of the Pennsylvania, Philadelphia, Sindhu K. Srinivas, MD, MSCE, agreed with Kawakita.

She noted, “This study shows that it’s not just pregnancy itself but underlying health conditions that are contributing to the persistently high severe maternal morbidity rates, especially the growing burden of chronic hypertension and obesity. These findings highlight the urgent need to focus on care for chronic diseases before and during pregnancy as important ways to optimize maternal health outcomes.”

Neither Kawakita nor Srinivas reported having any relevant conflicts of interest.