Severe Maternal Morbidity (SMM) In the U.S.

6 min read

Key Points

  • Severe maternal morbidity disproportionately affects Black women
  • A significant proportion of severe maternal morbidity and mortality events are preventable
  • Providers need to have a standard way of tracking SMM and guidelines on how to manage their rates


Article Written by: Jess Kimball

The United States has the highest maternal mortality rate of developed countries, and it is still rising. Neel Shah, who studies safety in pregnancy, says that four out of five of these deaths occur in the time before and after childbirth. In order to lower maternal morbidity, we need to understand when it is happening and why. Maternal deaths in the United States number about 650 to 750 annually. Severe maternal morbidity (SMM), on the other hand, affects approximately 50,000 to 60,000 people each year, and the numbers are increasing. Pregnancy-related deaths in the United States have doubled between 1987 and 2014, according to the Centers for Disease Control and Prevention (CDC).


Severe maternal morbidity is the term coined by the CDC to describe potentially life-threatening complications of pregnancy and childbirth. 

Increases in maternal age, re-pregnancy obesity, preexisting chronic medical conditions, and cesarean delivery may play a role in increased SMM. The CDC says that “Tracking and understanding patterns of SMM, along with developing and carrying out interventions to improve the quality of maternal care are essential to reducing SMM.”


What is severe maternal morbidity?

The Center for Disease Control and Prevention (CDC) has identified 21 indicators that make up the most widely used measure of severe maternal morbidity. 1.4% of those 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 people experiencing severe maternal morbidity every year.


The 21 indicators and diagnoses are:

  1. Acute myocardial infarction
  2. Aneurysm
  3. Acute renal failure
  4. Adult respiratory distress syndrome
  5. Amniotic fluid embolism
  6. Cardiac arrest
  7. Conversion of cardiac rhythm
  8. Disseminated intravascular coagulation
  9. Eclampsia
  10. Heart failure
  11. Puerperal cerebrovascular disorders
  12. Pulmonary edema
  13. Severe anesthesia complications
  14. Sepsis
  15. Shock
  16. Sickle cell disease with crisis
  17. Air and thrombotic embolism
  18. Blood products transfusion
  19. Hysterectomy
  20. Temporary tracheostomy
  21. Ventilation


What is the most common market of maternal morbidity?


Blood transfusions. 

Transfusions are recorded in more than 50% of cases of shock, amniotic fluid embolism, sickle cell disease with crisis, and disseminated intravascular coagulation. They are reported as co-occurring with more than a third of conditions associated with severe maternal morbidity. The overall rate of SMM increased almost 200% over the years, from 49.5 in 1993 to 144.0 in 2014. This increase has been mostly driven by blood transfusions, which increased from 24.5 in 1993 to 122.3 in 2014. After excluding blood transfusions, the rate of SMM increased by about 20% over time, from 28.6 in 1993 to 35.0 in 2014.


The second most common occurrences are hysterectomy and ventilation. The rate of hysterectomy increased about 55% over time, from 6.9 in 1993 to 10.7 in ­2014. The rate of ventilation or temporary tracheostomy increased by about 93% over the years, from 4.1 in 1994 to 7.9 in 2014.


What are comorbidities?

Comorbidities describe underlying health issues. These make it hard to measure SMM. Researchers from CMQCC, Stanford University, and the University of California, Berkeley developed an obstetric comorbidity scoring system for predicting SMM and non-transfusion SMM. The goal for these scoring systems is to facilitate improved comparisons of SMM rates and non-transfusion SMM rates between hospitals.

The most common comorbidities are hypertensive disorders of pregnancy (34.7%), previous cesarean delivery (15.7%), diabetes mellitus (10.5%), pre-existing hypertension (10.2%), and multiple gestation (9.8%).


What are the risk factors?

  1. Pre-pregnancy overweight and obesity
  2. Advanced maternal age
  3. Pre-existing hypertension and diabetes
  4. Smoking



Racial Disparities in SMM

The reported incidence of severe maternal morbidity is twofold to threefold higher among Black American birthing people compared with non-Hispanic White birthing people. The difference may be less pronounced, but is also higher among Hispanic, Asian and Pacific Islander, and Native American birthing people. 


“Severe maternal morbidity disproportionately affects Black women. We know these differences are not genetic in etiology, but most likely due to structural racism and neighborhood-level risk factors,” says Jessica R. Meeker, PhD, MPH.


At Penn State researchers found that white race was the only statistically significant, individual-level characteristic that was associated with lower odds of severe maternal morbidity. In terms of neighborhood-level factors, multiple characteristics were associated with an increased rate of severe morbidity. The rate of severe maternal morbidity increased by 2.4 percent in a given Census tract with every 10% increase in the percentage of individuals in the neighborhood who identified as Black or African American. There was also a 3%increase in the rate of severe maternal morbidity as the number of violent crimes in a given neighborhood increased.


Dr. Lisa Levine says that “Investing in neighborhoods that have been historically segregated, lacked access to government services, and subjected to racism will help to improve not only severe maternal morbidity, but also a host of other health outcomes for patients.”


As more research is conducted, more policies and initiatives are created. Discussing severe maternal morbidity sparks change and action!


How can we reduce disparities?

A significant proportion of severe maternal morbidity and mortality events are preventable.


  • Education and Communication about Disparities: Educating clinicians and staff about racial and ethnic disparities in maternal outcomes, the importance of shared decision making, cultural competency, and implicit bias are important steps to address disparities in care. 
  • Improving Delivery and Hospital Care Through Quality Initiatives: Provider factors such as inappropriate or delay in diagnosis or treatment and system factors such as communication failures and procedures not in place or not followed are common preventability factors.
  • New Models of Antenatal Care: Some hospitals are trying patient centered models such as Centering Pregnancy. 
  • Reinforcing Preconception and Postpartum Care: Preconception care is an opportunity to target disparities in maternal morbidity. Elevated rates of obesity, hypertension, diabetes, and chronic illness among racial and ethnic minority women have strong links with adverse maternal outcomes. A focus on preconception care is crucial.

Rates of unintended pregnancies are higher among black women, and these pregnancies are associated with elevated risk of adverse outcomes.


In order to reduce these disparities, we need to acknowledge and discuss them. Providers need to have a standard way of tracking SMM and guidelines on how to manage their rates. Through education, new models of care, preconception and postpartum care, and improving quality in facilities we can decrease this disparity and decrease severe maternal morbidity all together. 


If you are expecting and are concerned about severe maternal morbidity, try these tips:

  1. Research your hospital's SMM rate and make note of disparities that may affect you.
  2. Increase your support through care from a doula. 
  3. Increase your personal education.
  4. Discuss possible comorbidities that may affect you with your provider. Make note of these in your birth plan. Remember, the provider you see regularly may not be the one delivering your baby. 
  5. Plan postpartum support. Whether it’s hiring a mother's helper or postpartum doula or just planning for your partner to be home more in the immediate weeks postpartum, having help is necessary for adequate healing. 

Ultimately, it is your provider's responsibility to care for you, but there is a certain level of confidence and empowerment that comes from caring for yourself too. All of these tips support a better birth and postpartum experience for any parent, regardless of risk of SMM. 





CDC. (2021, February 2). Severe maternal morbidity in the United States. Centers for Disease Control and Prevention. Retrieved March 2, 2022, from


Department of Anesthesiology and the Division of Maternal Fetal Medicine, . (n.d.). Racial and ethnic disparities in death associated with... : Obstetrics & Gynecology. LWW. Retrieved March 2, 2022, from,Pacific%20Islander%2C%20and%20Native%20American


Howell E. A. (2018). Reducing Disparities in Severe Maternal Morbidity and Mortality. Clinical obstetrics and gynecology, 61(2), 387–399.


Leonard SA, Kennedy CJ, Carmichael SL, Lyell DJ, Main EK.  An Expanded Obstetric Comorbidity Scoring System for Predicting Severe Maternal Morbidity.(link is external) Obstet Gynecol. 2020 Sep;136(3):440-449.


Shah, N. (2018, October 16). A soaring maternal mortality rate: What does it mean for you? Harvard Health. Retrieved March 2, 2022, from


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