Severe Maternal Morbidity in the United States

Severe maternal morbidity (SMM) includes unexpected outcomes of labor and delivery that result in significant short- or long-term consequences to a woman’s health.¹ Using the most recent list of indicators, SMM affected more than 50,000 women in the United States during 2013–2014 and has been steadily increasing in recent years. This web report updates our previous report by adding information about SMM for 2013 and 2014, the 2 most recent years for which data are available on a national level.

It is not entirely clear why SMM is increasing, but changes in the overall health of the population of women giving birth may be contributing to increases in complications. For example, increases in maternal age,² pre-pregnancy obesity,^3,4 preexisting chronic medical conditions,^5,6 and cesarean delivery^2,7 have been documented. The consequences of the increasing SMM prevalence, in addition to the health effects for the woman, are wide-ranging and include increased medical costs and longer hospitalization stays.⁸ 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.

How Does CDC Identify Severe Maternal Morbidity?

To identify delivery hospitalizations with SMM, CDC uses administrative hospital discharge data and International Classification of Diseases (ICD) diagnosis and procedure codes. The original list of 25 SMM indicators based on the 9^th Revision of ICD was published in 2012.⁸ In October 2015, the United States transitioned to the 10^th Revision of ICD to code diagnoses and procedures. CDC, along with our clinical and public health partners, took the opportunity to review this new version of ICD coding to update the indicators, taking into account results from validation studies. The updated list of 21 indicators and corresponding ICD codes used to identify delivery hospitalizations with SMM for both ICD-9 and ICD-10 is displayed in the table below and can be used to track SMM when using administrative hospital discharge data from October 2015 and beyond.

Trends in Severe Maternal Morbidity

The following figures show trends over time in SMM in the United States in 2-year increments from 1993–2014 using data from the National Inpatient Sample.

Severe Maternal Morbidity, 1993–2014

This figure shows the rate of SMM per 10,000 delivery hospitalizations from 1993–2014. Women who received blood transfusions (procedure in which a patient is given donated blood generally in response to excessive bleeding around delivery) account for the greatest fraction of women with SMM. Hence, the SMM rates are shown for women with any indicator of SMM, women who had only transfusion as an indicator, and women who had some indicator other than transfusion.

The overall rate of SMM increased almost 200% over the years, from 47.6 in 1993–1994 to 141.6 in 2013–2014. This increase has been mostly driven by blood transfusions, which increased from 26.0 in 1993–1994 to 120.4 in 2013–2014. After excluding blood transfusions, the rate of SMM increased almost 40% over time, from 25.1 in 1993–1994 to 34.3 in 2013–2014.

Hysterectomy and Ventilation, 1993–2014

*After excluding blood transfusions

After excluding blood transfusions, the next most common SMM procedures are hysterectomy (surgical removal of the uterus) and mechanical ventilation (using a machine that helps a patient breathe). This figure shows the rate of hysterectomy and ventilation per 10,000 delivery hospitalizations from 1993–2014.

The rate of hysterectomy increased almost 60% over time, from 6.8 in 1993–1994 to 10.7 in 2013–­2014. The rate of ventilation increased by 75% over the years, from 4.1 in 1993–1994 to 7.2 in 2013–2014.

Disseminated Intravascular Coagulation, Adult Respiratory Distress Syndrome, and Acute Renal Failure, 1993–2014

This figure shows the rate of the most common SMM diagnoses (disseminated intravascular coagulation, adult respiratory distress syndrome, and acute renal failure) per 10,000 delivery hospitalizations from 1993–2014. Disseminated intravascular coagulation is a serious condition in which normal clotting is disrupted, resulting in excessive bleeding. Adult respiratory distress syndrome occurs when lung tissues become inflamed and fluid builds up in the lungs, preventing enough oxygen from getting into the blood. Acute renal failure is when the kidneys suddenly stop working.

Disseminated intravascular coagulation fluctuated through the years, but overall, increased by about 65% over time, from 4.5 in 1993–1994 to 7.4 in 2013–2014. Adult respiratory distress syndrome increased almost 2-fold over time, from 2.0 in 1993-1994 to 5.7 in 2013–2014. Acute renal failure increased by almost 4-fold over the years, from 1.1 in 1993–1994 to 5.1 in 2013–2014.

References

1. American College of Obstetricians and Gynecologists and the Society for Maternal–Fetal Medicine, Kilpatrick SK, Ecker JL. Severe maternal morbidity: screening and review . Am J Obstet Gynecol. 2016;215(3):B17–B22.
2. Martin JA, Hamilton BE, Osterman MJK, Driscoll AK, Matthews TJ. Births: final data for 2015 [PDF – 1.63MB]. Nat Vital Stat Rep. 2017;66(1).
3. Hinkle SN, Sharma AJ, Kim SY. Prepregnancy obesity trends among low-income women, United States, 1999–2008. Matern Child Health J. 2012;16(7):1339-1348.
4. Fisher SC, Kim SY, Sharma AJ, Rochat R, Morrow R. Is obesity still increasing among pregnant women? Prepregnancy obesity trends in 20 states, 2003–2009. Prev Med. 2013;56(6):372-378.
5. Campbell KH, Savitz D, Werner EF, Pettker CM, Goffman D, Chazotte C, Lipkind HS. Maternal morbidity and risk of death at delivery hospitalization. Obstet Gynecol. 2013;122(3):627–633.
6. Small MJ, James AH, Kershaw T, Thames B, Gunatilake R, Brown H. Near-miss maternal mortality: cardiac dysfunction as the principal cause of obstetric intensive care unit admissions. Obstet Gynecol. 2012;119(2 Pt 1):250–255.
7. Barber EL, Lundsberg LS, Belanger K, Pettker CM, Funai EF, Illuzzi JL. Indications contributing to the increasing cesarean delivery rate. Obstet Gynecol. 2011;118(1):29–38.
8. Callaghan WM, Creanga AA, Kuklina EV. Severe maternal morbidity among delivery and postpartum hospitalizations in the United States. Obstet Gynecol. 2012;120(5):1029–1036.