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Severe Maternal Morbidity in the United States: A Primer

pregnant woman aerial shot looking over water on pier
  • As many as 60,000 women in the U.S. experience unexpected outcomes during labor or delivery that have serious short- or long-term effects on their health and well-being

  • A greater health system and policy focus on maternal health before, during, and after childbirth is needed to prevent deaths related to pregnancy and address inequities

  • As many as 60,000 women in the U.S. experience unexpected outcomes during labor or delivery that have serious short- or long-term effects on their health and well-being

  • A greater health system and policy focus on maternal health before, during, and after childbirth is needed to prevent deaths related to pregnancy and address inequities


Maternal mortality rates are a key indicator of the health and well-being of a society. Yet this measure does not capture everything related to maternal health and well-being. It is also crucial to track:

  • “Near miss” events that could have resulted in death.
  • Severe maternal morbidity, defined by the U.S. Centers for Disease Control and Prevention as “unexpected outcomes of labor and delivery that result in significant short- or long-term consequences to a woman’s health.”
  • Serious illnesses that occur during pregnancy, like ectopic pregnancy, and the postpartum period, like cardiomyopathy.

A richer understanding of maternal health before, during, and after childbirth is a foundation for developing safer, more effective approaches to maternal care. While maternal deaths in the United States number about 650 to 750 annually, severe maternal morbidity affects approximately 50,000 to 60,000 women each year, and the numbers are increasing. As with maternal deaths, many cases of maternal morbidity can be avoided.

This report describes the severity and breadth of the maternal morbidity crisis in the U.S. and shows why addressing it is critical to advancing maternal health equity. A companion to Maternal Mortality in the United States: A Primer, it is the latest in a series of Commonwealth Fund publications investigating the causes of poor maternal outcomes — including stark racial inequities — and identifying potential solutions.


  • Maternal morbidity is emerging as an important measure in efforts to prevent maternal mortality and address maternal health inequities.
  • Each year, as many as 60,000 U.S. women are affected by severe maternal morbidity — unexpected outcomes of labor or delivery that have serious short- or long-term health impacts. In most instances, these outcomes could have been avoided with timely, appropriate care.
  • Broadening the definition of severe maternal morbidity to also encompass serious illnesses during pregnancy and postpartum reveals the broader scope of the problem as well as the need for further measurement efforts and policy intervention.

The U.S. Centers for Disease Control and Prevention (CDC) and the American College of Obstetricians and Gynecologists (ACOG) have offered detailed recommendations for monitoring and review of severe pregnancy and delivery complications. Both recommend facility-level, multidisciplinary review of all cases using a two-factor scoring system that identifies severe maternal morbidity by: 1) admission to the intensive care unit (ICU) and/or 2) transfusion of four or more units of blood products at any time from conception through 42 days postpartum. The scoring system, developed by Stacie Geller and colleagues, has been validated and can be used in real time in hospital settings, unlike administrative datasets currently used for population-level surveillance. To date, severe maternal morbidity reviews remain rare, having been implemented in individual facilities in California, and Illinois recently piloted a statewide operation through its regionalized perinatal system. In the future, severe morbidity reviews may increase as more hospital systems assess their experience with severe morbidity and states expand the scope of their maternal mortality reviews.

We recognize that not all people who become pregnant and give birth identify as women. While we use the gender-inclusive term “birthing people” as much as possible, we use “woman,” “women,” and “maternal” to conform with the language in externally published research findings.

What Do We Mean by Maternal Morbidity?

Measuring severe maternal morbidity is challenging. It requires addressing not only the impact of comorbidities — whether a particular health problem results from pregnancy or from, say, a chronic health condition — but also the effects of discrimination, racism, and access to health care (see Figure B on page 12 of the National Quality Forum report). Researchers and others must also establish reliable ways to capture data on maternal health conditions across different measurement systems and care settings. Finally, they need to consider conditions that manifest during pregnancy or postpartum, not just during the birth event.

There are several levels of maternal morbidity. In decreasing order of severity, they are:


Traditionally a reliable measure meets multiple criteria, such as being clinically relevant, accurately detecting true cases of a condition, and being based on data that are reliably collected across multiple settings. In the U.S., the most common definition, developed by the CDC, is based on 21 indicators (16 diagnoses and five procedures) identified by an array of diagnostic codes assigned at the time of birth. This measure has the advantage of being easily applied to hospital discharge data either locally or in national datasets. Unfortunately, it may not capture illnesses or complications that manifest before or after the birth hospitalization, with past research finding between 14 percent and 22 percent additional new cases postpartum. Expanding this measure to include assessment of severe maternal morbidity after birth and into the postpartum period is important for obtaining a true picture of maternal morbidity and crafting appropriate interventions.


Most pregnancies are uncomplicated and result in a healthy mother and baby. This exhibit illustrates the rarity of severe illness among the 3.7 million births in the U.S. annually.


This exhibit depicts the prevalence of various conditions that can occur during pregnancy, childbirth, and the postpartum period. Because reporting of these rates is not based on a single study, the rates are not always comparable. The studies cited here drew from different data sources and focused on different populations; they also used slightly varying definitions of measures or time periods. For some conditions, including miscarriage, hyperemesis gravidarum (extreme, persistent nausea, and vomiting during pregnancy), and endometritis (inflammation of the inner lining of the uterus), prior analyses produced only a range of estimates.

Conditions such as gestational diabetes and hypertension, hyperemesis gravidarum, and prenatal depression are not typically life-threatening. But they occur frequently and affect hundreds of thousands of women each year. If these conditions are not monitored, they can have serious consequences for birthing people and their families.


The CDC has identified 21 indicators (16 diagnoses and five procedures) drawn from hospital records at the time of childbirth, that make up the most widely used measure of severe maternal morbidity. Approximately 140 of 10,000 women (1.4%) giving birth in 2016–17 had at least one of those conditions or procedures. If that rate were applied to the 3.6 million U.S. births in 2020, the result would be approximately 50,500 women experiencing severe maternal morbidity every year.


Blood transfusion is the most common marker of severe morbidity. If the rate shown here were applied to current births, transfusions would have occurred in approximately 37,000 births in 2020.

Transfusions have consistently been a significant component of severe maternal morbidity measures, in large part because the need for a transfusion distinguishes the severity of conditions that may otherwise not be considered life-threatening. Transfusions are recorded in more than half of cases of shock, amniotic fluid embolism, sickle cell disease with crisis, and disseminated intravascular coagulation. Overall, transfusions co-occur with more than a third of the conditions associated with severe morbidity. Over time, most of the increase in the severe maternal morbidity rate has come with an increase in blood loss requiring transfusions.


Comparative data on severe maternal morbidity across different countries are limited. However, we can compare blood transfusion rates during childbirth in the U.S. and selected European countries and regions. The U.S. reports the highest transfusion rate during childbirth among these countries.


Differences in severe maternal morbidity among races and ethnicities are particularly pronounced. Non-Hispanic Black mothers are more than twice as likely as non-Hispanic white mothers to experience severe maternal morbidity — comparable to the differences in maternal mortality rates between Black and white women.

Difference among age groups show peaks in the extremes, with a higher rate of severe illness among very young mothers, the lowest rate reported for mothers ages 25 to 29, and the highest rate for women age 40 and older. Rates of severe illness are also higher among women in the Northeast and South, those from lower-income communities, and those giving birth in public hospitals.


Combining data on women’s race and type of health insurance reveals even more pronounced disparities. A study based on New York City hospital data found wide disparities in maternal morbidity between races. It also found disparate maternal morbidity rates among women with different types of insurance — and startling disparities when taking the two factors into consideration. Additional studies indicate that these inequities persist into the postpartum period.


A study of Massachusetts women found the likelihood of returning to the hospital in the six weeks following birth was more than twice as high among women who experienced severe maternal morbidity, regardless of whether they had required a transfusion. This pattern held even after controlling for a wide range of possible factors, including race/ethnicity, pregnancy-related conditions, education, method of delivery, insurance status, and whether it was their first birth or not. The differences in rehospitalizations for women with severe maternal morbidity were smaller, but still pronounced between six weeks and one year after birth.


The much higher cost of births involving severe maternal morbidity is mostly because of expenses related to birth. During the prenatal and postpartum periods, births that involve severe maternal morbidity cost about 40 percent more than births that do not. This is true regardless of whether one has commercial insurance or Medicaid.


An examination of severe maternal morbidity reveals the much broader scope of challenges associated with improving maternal health in the United States than does a focus on maternal mortality alone. For every maternal death, there are 70 to 80 cases of severe illness — and that includes only cases identified at the time of birth. And expanding the perspective to the prenatal and postpartum periods shows that problems run even deeper.

Many health conditions related to pregnancy, childbirth, and the postpartum period can be prevented with timely care. Yet for many birthing people, especially those of color and those with public health coverage, such care has not been readily available or affordable. Inconsistencies in coverage have been linked to gaps in perinatal care. Systems established to prevent severe maternal morbidities will have the added effect of reducing maternal deaths.

There is also a pressing need for more comprehensive and culturally appropriate maternal care at the community and hospital levels and more intentional focus on subdomains that incorporate the role of health equity and intervening in structural racism. A focus on a reproductive justice framework in clinical training and practice has been proposed as one approach to addressing long-standing inequities in our system. The goal is to address issues in women’s health before pregnancy so they enter pregnancy healthier, begin prenatal care earlier, and are less likely to develop the conditions that lead to severe morbidity.

Policies that extend pregnancy-related coverage for a year after childbirth, a change made more feasible for state Medicaid programs since enactment of the American Rescue Plan, would also provide critical protection. Finally, the adoption of “high value” models of care, such as greater reliance on birth centers, midwifery care, and use of doulas, hold promise for improving maternal health outcomes.

Improving Measurement

Policies that promote more rigorous health equity measurement are also important. With funding from the Centers for Medicare and Medicaid Services (CMS), a National Quality Forum (NQF) committee assessed the state of maternal morbidity and mortality measurement and developed the following recommendations, among others:

  • Use stratified measurement approaches focused on patient experience by race and ethnicity.
  • Develop clear evidence-based screening protocols and monitor protocol compliance.
  • Develop a quality dashboard to share data and report family experiences in a transparent manner.
  • Track outcomes of uninsured populations and the impact of Medicaid eligibility expansion on outcomes.

To accelerate measurement related to reducing severe maternal morbidity, CMS adopted two new maternal morbidity structural measures (effective October 2, 2021). To report on these measures, hospitals will respond annually to a two-part question:

  1. Does your hospital or health system participate in a statewide and/or national perinatal quality improvement collaborative program aimed at improving maternal outcomes during inpatient labor, delivery and postpartum care?
  2. Has your hospital implemented patient safety practices or bundles related to maternal morbidity to address complications, including, but not limited to, hemorrhage, severe hypertension/preeclampsia or sepsis?

How We Conducted This Study

These exhibits are based on data from a wide range of sources. There is no single international standard for the measurement of severe maternal morbidity (SMM), but within the U.S. an algorithm developed by the Centers for Disease Control and Prevention (CDC) is most widely used in large part because it is relatively easy to apply to a wide range of datasets. As a result, many researchers have used it as a foundation for studies of different aspects of severe maternal morbidity and these various studies are the foundation for this primer. Of particular importance were recent studies from Brown et al. looking at SMM nationally for 2016–17 and Fingar et al. examining national data from 2015 on SMM. Because there isn’t comprehensive, national reporting on the frequency of conditions manifested during pregnancy and in the postpartum period, rates of such conditions were identified from individual studies. Since these studies involved different datasets and periods, the findings are not necessarily comparable. However, they do provide an overview of the prevalence of these conditions.

We are grateful to those researchers who compiled the studies and to Ebere Obaraeke who assisted with the collection and presentation of these data.


The authors thank Kay Johnson of Johnson Group Consulting for her review and helpful comments on this primer.

Publication Details



Eugene Declercq, Professor, Community Health Sciences, Boston University School of Public Health


Eugene Declercq and Laurie Zephyrin, Severe Maternal Morbidity in the United States: A Primer (Commonwealth Fund, Oct. 2021).