Prepregnancy BMI and risk of severe maternal morbidity and mortality


A study published in JAMA Network Open found that maternal prepregnancy obesity in the United States is associated with an elevated risk of severe maternal morbidity (SMM) and/or mortality.

Heather Frey

Heather Frey, MD, MSCI

“Maternal mortality rates in the U.S. are higher than other countries with similar resources; therefore, advancing our understanding of factors that contribute to the maternal death rate is critical,” said principal investigator Heather Frey, MD, MSCI, an associate professor of maternal-fetal medicine at The Ohio State University in Ohio.

Frey noted that obesity, which affects about one-third of pregnant women, is a known risk factor for complications, such as diabetes and hypertension, in pregnancy and is associated with higher rates of mortality in non-pregnant women. “However, some of the previous research is conflicting as to the association between obesity and SMM, so we wanted to better understand this relationship,” she said.

The study accessed the vital records and linked Medicaid claims data in the state of Ohio from January 2012 to December 2017 to determine both mortality and SMM from 20 weeks’ gestation through 1-year postpartum.

In the cohort of 347,497 pregnancies among 276,691 Medicaid beneficiaries, the median maternal age at delivery was 25 years, of whom 60.6% were non-Hispanic White women. The prevalence of maternal obesity was 30.5%.

Composite SMM and/or mortality outcome occurred in 5.3% of pregnancies.

The adjusted risk ratio for an elevated risk of SMM and/or mortality during pregnancy to 1-year postpartum compared to a healthy body mass index (BMI) was 1.07 (95% confidence interval [CI]: 1.03 to 1.11) for overweight (25.0 -- 29.9 BMI); 1.19 (95% CI: 1.13 to 1.24) for class 1 obesity (30.0 -- 34.9 BMI); 1.37 (95% CI: 1.30 to 1.44) for class 2 obesity (35.0 --39.9 BMI); and 1.71 (95% CI: 1.63 to 1.80) for class 3 obesity (≥40.0 BMI).

Results were comparable when the follow-up period was shortened to 42 days postpartum or the delivery hospitalization.

Hypertension mediated 65.1% of the association between obesity and SMM and/or mortality.

“While we were not surprised that hypertension was a mediator, the proportion of the relationship between obesity and the outcome that was explained by hypertension was higher than expected,” Frey told Contemporary OB/GYN. “This highlights the need to develop and implement effective interventions to reduce the risk of hypertensive complications during pregnancy, particularly among obese women.”

The frequency with which women experienced different morbidities within the timeframe also differed by maternal BMI class. For instance, women with increased BMI had high rates of sepsis, while transfusion was the most common indicator of SMM in those with lower BMI when assessed through 42 days postpartum.

“Our data suggest that women who are obese may require increased medical surveillance during pregnancy and, perhaps more importantly, after delivery,” Frey said. “Interventions to improve the delivery of postpartum care and enhance the transition of care from the obstetrician to a primary care provider are needed.”

The study also underscores the importance of identifying and managing hypertensive disorders in pregnant women, particularly those with obesity.

“Unfortunately, efforts to reduce rates of obesity in the U.S. have been largely ineffective on a population level,” Frey said. “On the individual level, though, weight reduction strategies should be employed prior to conception, which starts with appropriate counseling in the preconception period.”

But there is no perfect approach, so discussions and interventions must be tailored to the individual patient, according to Frey. “In the appropriate patient who is interested and motivated to pursue weight-loss surgery, referrals prior to conception should be facilitated,” she said.

Meanwhile, obesity is one of the most common medical comorbidities of pregnancy, and rates of obesity in the pregnant population are expected to continue to increase over the next decade. “Thus, improving our understanding of the risks associated with this condition, then identifying effective interventions to improve the health of pregnant individuals with obesity, are imperative,” Frey said.


1. Frey HA, Ashmead R, Farmer A, et al. Association of prepregnancy body mass index with risk of severe maternal morbidity and mortality among Medicaid beneficiaries. JAMA Netw Open. Published online June 28, 2022. doi:10.1001/jamanetworkopen.2022.18986

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