Cutting-edge medical advances and innovative technologies have made headlines and continue to flourish in the new millennium. However, these medical achievements stand in stark contrast to the paradoxical increase in US maternal mortality, which is among the highest of all developed nations.1 Why are our mothers dying? The question and, more importantly, the answers are complex. Maternal mortality is a multidimensional phenomenon encompassing: barriers to health care access; racial and ethnic disparities; concurrent escalating maternal comorbidities including obesity, diabetes and hypertension; inadequate perinatal science and translational perinatal medicine; and variable reporting statistics which only recently enhanced ascertainment of cases. With this issue, Contemporary OB/GYN begins a year-long commitment to raising awareness, detailing etiologies and providing clinically relevant algorithms for the management of life-threatening maternal complications in an effort to mitigate this tragedy.
Maternal mortality ratio (MMR) is defined as pregnancy-related deaths per 100,000 live births. Globally, the MMR was 282 (95% uncertainty interval (UI) 264-300) in 1990 and decreased to 196 (173-224) in 2015, falling by 30%. In contrast, the United States MMR rose from 16.9 (16.2-17.8) in 1990 to 26.4 (24.6-28.4) in 2015, climbing more than 56%.1 Among 31 Organization for Economic Cooperation and Development countries reporting maternal mortality data, the United States ranked second from the bottom.2 In contrast, during this same time period, the MMR remained relatively low in Canada, increasing slightly from 6.0 (5.2-6.9) in 1990 to 7.3 (6.2-8.7) in 2015. This discrepancy between neighboring countries seems incomprehensible, particularly considering that Canada has a lower per capita income. With over 4 million American women giving birth annually, this is not a statistical aberration, it is a medical catastrophe. Our mothers deserve so much more.
Although the statistics are sobering, the addition of “pregnancy question formats” to death certificate data introduced in 2003 account for some of the apparent increase. To counteract underreporting of maternal deaths in the National Vital Statistics system, a pregnancy question with checkboxes was introduced in 2003 but has had differential state update. The goal of the question was to ascertain whether women were pregnant at the time of death or within 1 year of pregnancy. MacDorman et al. have estimated that as much as 79.9% of the total increase in maternal mortality since the new millennium may be due to improvement in ascertainment.2 However, adjustment for ascertainment bias should not diminish our national shame in having one of the highest maternal mortality rates in the industrialized world.
Definitions, Risk Factors, Etiologies
Any discussion of maternal mortality must commence with its definition. The World Health Organization (WHO) characterizes maternal mortality as death of a woman occurring while pregnant or within 42 days of termination of pregnancy regardless of the length or location of that pregnancy due to a direct or pregnancy-aggravated cause. Late maternal deaths extend beyond 42 days up to 1 year beyond the index pregnancy.3 In the United States, the Centers for Disease Control and Prevention (CDC) reports MMR through the Pregnancy Mortality Surveillance System (PMSS) identifying pregnancy-related deaths during and up to 365 days postpartum. The PMSS acquires MMR through review of maternal death certificates linked to fetal death and birth certificates. It designates maternal mortality as those maternal deaths that are the result of a “pregnancy complication, a chain of events initiated by pregnancy, or the aggravation of an unrelated condition by the physiologic effects of pregnancy.”4 Pregnancy-associated deaths identified as maternal deaths during pregnancy or within 1 year of the end of pregnancy from a cause that is unrelated to pregnancy are excluded from the MMR. While these categorical distinctions are robust, they may underestimate maternal deaths from such important etiologies as suicide or intimate partner violence.5,6 As part of our special series, we plan to explore the nuances of case definitions and ascertainment of cases of maternal death in a dedicated article.
Now that we have defined maternal mortality, we can examine risk modifiers. Geography appears to significantly impact the rate of maternal mortality and may be a surrogate for variable timing in implementation of the death certificate pregnancy question, disparate funding of state-wide healthcare systems, and heterogeneous population demographics. For example, the MMR was 35.8 in 2014 in Texas, the highest of any state, compared to 15.1 in California, which is the only state to report a declining MMR.2 Examination of MMR by race and ethnicity uncovers considerable disparities. Creanga et al. reported that non-Hispanic black women had a 3.4-fold increased MMR compared to non-Hispanic white women based on 2011-2013 pregnancy-related mortality data.7 Age is also a significant risk factor with MMR increasing for all women with age peaking in those mothers age 40 or older. This has particular relevance since the percentage of pregnant women aged 35 or older compared to all women continues to increase.8 Race and age synergistically increase maternal mortality among black women aged 40 and older who have the highest risk of maternal death with an MMR of 191.6 according to the 2011-2013 PMSS data. Pre-pregnancy maternal weight also significantly influences maternal mortality. Lisonkova et al. reported that both extremes (underweight versus overweight) of body mass index (BMI) negatively impacted maternal morbidity and mortality.9 However, those with class 3 obesity corresponding (BMI ≥ 40) had an absolute risk adjusted rate difference per 10,000 women of 61.1 (95% CI, 44.8-78.9) deaths compared to pregnant women with normal BMI. While the absolute risk may be small, mothers with multiple risk factors have a compounded danger leading to a logarithmic increased threat of maternal mortality.
What are the specific etiologies of maternal mortality? In 2017, the CDC reported that cardiovascular disease including cardiomyopathy accounted for the highest proportion of the causes of maternal mortality (26.5%,) followed by: other medical non-cardiovascular disease (14.5%), infection/sepsis (12.7%), hemorrhage (11.4%), thrombotic pulmonary embolism (9.2%), hypertensive disorders of pregnancy (7.4%), cerebrovascular accident (6.6%), amniotic fluid embolism (5.5%) and anesthesia complications (0.2%).7 Identification of cardiovascular disease as the leading cause of maternal death in the United States is surprising. It is, therefore, appropriate that Contemporary OB/GYN begins its special series on maternal mortality with this topic. Data released from the 2017 CDC Maternal Mortality Review Information Application (MARIA platform) also recognize maternal cardiovascular disease as the major etiology leading to pregnancy-related death.4 These data also reveal that the majority of maternal deaths (44.4%) occur during the first 6 weeks after pregnancy, highlighting that delivery of the fetus does not signify the end of maternal risk for morbidity and mortality.
Are maternal deaths preventable? The literature reports that 20% to 50% of maternal deaths may be preventable.10,11 In 2017, data from the CDC MARIA platform reported that 59% of maternal deaths are preventable. This statistic tells us that we have a lot of work to do. Our systems of care must become more proactive and comprehensive for maternal care encompassing antepartum, intrapartum, postpartum and inter-conception care. The first Scientific Statement on Maternal Cardiac Arrest by the American Heart Association* has underscored the tremendous research gaps in maternal resuscitation science.12 Granularity of data capturing details surrounding each maternal death will only be achieved with maternal registries that utilize pregnancy-specific variables that are accessible nationally and maintained with transparency and high fidelity. Better data will facilitate our understanding of maternal pathophysiology and lead to improved maternal care and ultimately better maternal outcomes. Institutional preparedness through simulation training will lead to improvement in medical team performance and communication during the management of obstetrical emergencies. Developing a culture of safety also applies to any location where maternal care takes place. Use of checklists and early warning tools such as the “Obstetric Early Warning Score” has been demonstrated to reduce maternal morbidity and even mortality.13,14
It is hard to imagine that the rise in US maternal mortality rates has had to become a crisis in order to garner our attention. Now that we know about it, we as a society and as health care providers must dedicate ourselves to protecting each mother. While pregnancy is not generally regarded as a disease,15 the unique physiologic adaptations required for the maintenance of pregnancy create a susceptibility to potentially life-threatening illness. We must harness all of our technological ingenuity and medical expertise to conquer maternal mortality. Our mothers are in dire need and are most deserving, worthy of only the best that medical science can offer and deliver.
Disclosures: The author reports no potential conflicts of interest with regard to this article.
1. Kassebaum N et al. Global, regional, and national levels of maternal mortality, 1990-2015: A Systematic analysis for the Global Burden of Disease Study 2015. Lancet. 2016; Oct 8; 388: 1775-1812.
2. MacDorman MF, Declercq E, Cabral H, Morton C. Recent Increases in the U.S. Maternal Mortality Rate: Disentangling Trends from Measurement Issues. Obstet Gynecol. 2016; 128(3):447-455.
3. World Health Organization. Health statistics and information systems. http://www.who.int/healthinfo/statistics/indmaternalmortality/en/ Accessed November 22, 2017.
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