We don’t really know how many pregnant people are dying in the US

We don’t really know how many pregnant people are dying in the US

The US is not a stranger to maternal mortality. The country has gained notoriety for having the highest maternal death rate of similarly wealthy nations; on a global ranking, the US falls 55th, just behind Russia and just ahead of Ukraine. Around 800 pregnant Americans die each year–though those numbers have spiked since the COVID pandemic–and the Centers for Disease Control and Prevention (CDC) reports that two-thirds of these pregnancy-related deaths are preventable. In other words, more than 500 mothers die each year unnecessarily.

[Related: COVID deaths in pregnant people in the US are flying under the radar]

These vital statistics are crucial for forming maternal healthcare policy. However, the data on mortality rates is more complicated than one might think. There are three systems that track maternal mortality. Each system has its own limitations on how information is analyzed. And as the country enters an era with increasingly strict restrictions on abortion and maternal care, properly measuring and understanding these numbers is crucial for creating support systems and saving lives.

What does it mean to be dead?

When someone dies, a code is assigned to indicate the cause. “W67,” for example, refers specifically to a death from accidentally drowning in a swimming pool. “J14” is death from pneumonia, but just from the Hemophilus influenzae bacteria. And “O72.2” is when a mother dies from excessive blood loss more than 24 hours after giving birth. This information is recorded on death certificates by physicians, medical examiners, coroners, and any other contributing causes. It’s a clinical process that occurs at the end of an emotional experience. Experts collect and analyze the codes for deaths across the country to determine the causes of death. We can then create policies to address those causes.

“Births and deaths–this information is the foundation of our public health system,” says Marie Thoma, a reproductive and perinatal epidemiologist and professor at the University of Maryland.

In their research on maternal mortality, Thoma and her colleague Eugene Declercq, an Obstetrics and Gynecology professor at Boston University’s School of Medicine, have studied how the structure of these death certificates and informational processing systems has led to inconsistent and inaccurate data. Declercq states that people assume maternal mortality is straightforward because they see it on TV. This is a tragedy at birth. It’s more complex in reality. Experts must get this data right, he says, because “with maternal mortality, we’re talking 700 or so deaths per year and the mistakes [in analysis] are magnified, as opposed to analyzing overall death rates.”

How do we track maternal mortality in the US?

It is difficult to determine the exact maternal mortality rate for the entire country because there are three different systems that track this data. They operate in different ways.

The main difference between these systems is how the maternal deaths are defined. The National Vital Statistics System (NVSS), run by the CDC, is the country’s official source of maternal mortality data and is used for international comparisons. Maternal mortality, as defined by the World Health Organization and so adopted by the NVSS, is considered as the death of a person while pregnant or within 42 days of birth or termination of pregnancy. It also requires that the cause or aggravated of the death must be related to the pregnancy. (Not, for instance, from a suicide, or an accident. The Pregnancy Mortality Surveillance System (PMSS) is a broader measurement. It counts pregnancy-related deaths – people who died during or within one year of pregnancy and for reasons that are “from a pregnancy complication, a chain of events initiated by pregnancy, or the aggravation of an unrelated condition by the physiologic effects of pregnancy.” Maternal Mortality Review Committees (MMRCs) are multidisciplinary groups in states and cities that perform comprehensive reviews of deaths among women within a year of the end of a pregnancy. Although they have the most comprehensive data, they are not as complete as the other systems.

Maternal mortality graph showing three nested circles in blue, gold, and red
The timelines of the three death-tracking systems vary widely. Gene Declercq

These definitions are crucial because they influence how data is tracked. Do you remember the codes that indicate a person’s cause of death. There is a set of codes that can be used to identify obstetrics. They are called the “O” codes. Until 2003, identifying maternal deaths was tricky: States had their own systems and there was no way to consistently track whether the death of a pregnant person happened during pregnancy, a week after, or within the past year–the important distinctions that impact how the NVSS and PMSS systems define it. In 2003, the NVSS system introduced a checkbox on death certificates that offered consistent options for people to denote when someone died and their pregnancy status. But not all states adopted the policy until 2017 and it was still being filled out inconsistently–so the NVSS paused its reporting on maternal mortality rates from 2007 to 2018, when officials felt the data would be cleaner and more consistent.

The NVSS system has made two improvements to the system, one of which is limiting the age range of maternal mortalities to people under age 44, to have less potential data interference. This distorts data for older women. “It’s possible we may be underestimating [rates for] older women to some extent and perhaps still overestimating [rates] the younger ages,” says Bob Anderson, chief of the Mortality Statistics Branch at National Center for Health Statistics, which monitors the NVSS system. “But we believe that overall we are getting better information.”

The NVSS system double-checks records if the record has been marked for pregnancy. However, it is not as accurate as PMSS. The PMSS system uses medically-trained epidemiologists to review background information from births and fetal death certificates in order to determine the exact cause and time of death. Although it is more detailed, it can take a while to review.

” The NVSS system is more for situational awareness,” Anderson states. Anderson says that even though the actual level of maternal mortality may not be correct, we can still capture whether deaths are increasing or decreasing. The PMSS system can provide more explanations and more information about the true burden .”

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Together, these systems provide complementary information. The data is not shared between the programs that run the systems. Anderson claims that the logistics required to do that would require resources they don’t possess. Declercq and other researchers find this frustrating. They believe a simplified and more comprehensive dataset would allow them to better understand the problem and inform the solutions.

What do the statistics show?

Inaccurate maternal death data has serious implications. Maternal mortality is so specific that even a small amount of miscoding could lead to misleading statistics. Marion MacDorman, a research professor at the University of Maryland’s Population Research Center who passed away earlier this year, conducted a sensitivity analysis in 2017 to study how overreporting maternal deaths (which can happen when death certificates are filled out improperly) might influence mortality rates across different age groups. With just 1 percent of overreporting, maternal death rates among women older than age 40 more than tripled their mortality rate. This dataset is easy to use and make a significant impact on.

Anderson believes that the NVSS numbers work. He also recognizes the need to ensure that policymakers and health professionals have the best data. “If you produce numbers that are wildly inaccurate, it could lead to you developing interventions that aren’t necessary.” Anderson states that it could also give you a false sense or security, which can lead to you believing everything is fine when it isn’t.”

The disparity in numbers is already revealing curious results. For example, 2018 is the most recent year that both systems have reported their rates: the PMSS reported 17.4 deaths per 100,000 people and the NVSS system reported 17.4 deaths per 100,000. It’s curious, Declercq says, because the PMSS system includes deaths that occur over a longer time span (one year after birth, compared to the NVSS’ 42 days) and so, should typically be higher than the NVSS number. The PMSS rates have stayed relatively flat over the past few years, near 17 per 100,000, while the last time the NVSS reported numbers was in 2007: 12.7 deaths per 100,000. It is difficult to determine if the NVSS numbers have increased dramatically due to an increase in the number of pregnancy-related deaths or if it has decreased.

[Related: Why were chainsaws invented? To aid in childbirth. ]

Anderson believes it’s because the PMSS system can correct deaths that shouldn’t have been coded as matern. He also thinks that the PMSS system will likely reflect a similar increase in deaths because of COVID when they release reports on numbers from 2019 to 2021. There is no explanation for the similarity of these numbers.

The different definitions of maternal mortality and pregnancy-related deaths lead to different data analyses regarding the cause and timing. According to the PMSS numbers, one-third of all maternal mortalities occur after the 42-day period. Statistics from the NVSS don’t include deaths occurring after this time period.

The causes of maternal deaths vary greatly and depend on the time that mothers die. These data are based upon a report by maternal mortality review committees. Hemorrhage and cardiovascular diseases are the most common causes of death during pregnancy. Infection is the leading cause of death at birth and shortly thereafter. The leading causes of infection in the postpartum period are cardiomyopathy (weakened heart muscle) as well as mental health conditions (including suicide) which are often identified during the time the parents are out-of-hospital visits. It is important to understand these variations so that you can identify these conditions early and offer clinical interventions that could save lives.

“People think maternal mortality is kind of straightforward because they assume it’s what they’ve seen on TV, which is a tragedy at the time of birth.”

Eugene Declercq, Boston University’s School of Medicine

But what’s challenging is when certificates are reported in a way that skips the nuance of when mothers die. This shows up in the codes for late maternal deaths (42 days to a year after birth), which do not provide information about the actual cause of death (they just indicate “late maternal death”). Thoma and her colleagues conducted a study of 2016 to 2017 NVSS data and examined nearly 4,000 records for maternal mortality. Among the 1,691 records originally coded as maternal deaths, 43.5 percent were originally coded to non-specific causes. On her end, Thoma was able to recode 94.4 percent of these cases to more specific causes of death with more information from the death certificates, leaving only about 5 percent unspecified.

Breaching down these numbers, Declercq states, allows healthcare providers and patients to allocate resources where they are most needed. The number of deaths due to causes other than birth has decreased over time. However, the number of deaths from issues after birth has increased. Declercq believes this information should be useful in determining where professionals should focus their attention.

“Asking whether deaths occurred during pregnancy, at birth or after was a game-changer for all of it,” he says. “People began to see [maternal death] as more than a clinical problem. We need to reform the hospital procedures at the birth. This has been done a lot. It is not possible to save a woman’s life if she is dying from complications of her pregnancy. This is why you need to think about it at the community level .”

Who will fix the system?

Thoma is currently studying the impact of opioid use and suicide on maternal mortality. According to a 2021 CDC study, homicide, suicide, and drug overdoses are the leading cause of pregnancy-associated deaths, which include individuals who have died up to one year after birth. Thoma states that this information is often overlooked due to limitations in the definition of maternal mortality. This information can help to identify the best community support and medical care for new mothers during this time period, and reduce strain.

This became clear during the COVID pandemic, when the American Rescue Act created pathways for states to extend Medicaid coverage for pregnant people from 60 days to one year postpartum. State governments bear the responsibility for adopting the change, and health advocates have argued for an extension of Medicaid policy for new mothers from 60 days to a full year, which some say would help decrease the number of deaths. New plans from the White House earlier this year advocate for a similar change, and just last month, Hawaii, Ohio, and Maryland all approved this policy.

[Related: Black mothers contend with high death rates and climate change]

Not all states respond in the same manner. More researchers are studying how the recent reversal of Roe v. Wade might impact maternal mortality. Thoma states that places with less resources for maternal health or training on how to properly fill out death certificates correctly often have more inaccurate information on mortality rates, which means they have a poorer understanding of how pregnant women are dying. This raises concerns about the health of mothers and children, particularly considering that six states with the highest maternal deaths in the country quickly banned abortions.

This is “geeky” work but it’s essential to do because these policies reflect the US’s approach to maternal care. He notes that there is a lot to be learned from studying maternal deaths. This can also be applied to women’s health in general. It’s not only about pregnancy. It’s not about keeping women alive during pregnancy and then abandoning them after the baby is born. It’s about creating a system that allows women .”

to be as healthy and happy as possible.

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