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There is a recent report from the WHO about Maternal Mortality rate trends in the last 20 years. In this time the global Maternal Mortality Ratio (MMR, maternal deaths per 100,000 live births for women of reproductive age) has dropped 33%. A few countries, including the United States, have increased MMR. Looking at the Country profiles we can see that not only has the US MMR rate increased significantly, but the uncertainty interval of the estimate has increased many times. This pattern is not seen in other geographically/economically similar countries.

What is the reason for this change in quality of data and resulting increase in uncertainty of such a core feature of society?

United States United Kingdom
US MMR UK MMR
Mexico Japan
Mexico MMR Japan MMR
Canada Key
Canada MMR Key for MMR graphs
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    Does the WHO report say something about the sources they used to compile the data?
    – quarague
    Feb 28, 2023 at 12:28
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    @quarague From the Country profiles I think the data mostly comes from the "civil registration vital statistics system". Other sources are mostly "Country consultation 2015: CDC’s Pregnancy Mortality Surveillance System" from various years and a couple of data points from "Pregnancy - Related Mortality in the United States 2011-2013" and "Hoyert, 2022".
    – User65535
    Feb 28, 2023 at 14:00
  • Those are referenced in the key, with civil registration vital statistics system being CRVS, "Hoyert, 2022" miscellaneous and the other two specialized studies.
    – User65535
    Feb 28, 2023 at 14:41
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    Just a guess: Maybe an increase in home birthing, while most reliable MMR information comes from hospitals.
    – Barmar
    Feb 28, 2023 at 17:11
  • Not sure if this question is about politics, but interesting nonetheless. Feb 28, 2023 at 19:27

2 Answers 2

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The CDC Pregnancy Mortality Surveillance System website has this to say about it:

Since the Pregnancy Mortality Surveillance System was implemented, the number of reported pregnancy-related deaths in the United States steadily increased from 7.2 deaths per 100,000 live births in 1987 to 17.3 deaths per 100,000 live births in 2018. The graph above shows trends in pregnancy-related mortality ratios between 1987 and 2018 (the latest available year of data).

The reasons for the overall increase in pregnancy-related mortality are unclear. Identification of pregnancy-related deaths has improved over time due to the use of computerized data linkages between death records and birth and fetal death records by states, changes in the way causes of death are coded, and the addition of a pregnancy checkbox to death records. However, errors in reported pregnancy status on death records have been described, potentially leading to overestimation of the number of pregnancy-related deaths. Whether the actual risk of a woman dying from pregnancy-related causes has increased is unclear, and in recent years, the pregnancy-related mortality ratios have been relatively stable.

This section of the webpage also cites to:

Baeva S, Saxton DL, Ruggiero K, et al. Identifying maternal deaths in Texas using an enhanced method, 2012. Obstet Gynecol. 2018;131:762–769. The abstract to this paper states in the pertinent parts:

Results: Fifty-six maternal deaths were confirmed to have occurred during pregnancy or within 42 days postpartum. Using our enhanced method, the 2012 maternal mortality ratio for Texas was 14.6 maternal deaths per 100,000 live births, less than half that obtained using the standard method (n=147). Approximately half (50.3%) of obstetric-coded deaths showed no evidence of pregnancy within 42 days, and a large majority of these incorrectly indicated pregnancy at the time of death. Insufficient information was available to determine pregnancy for 15 obstetric-coded deaths, which were excluded from the 2012 maternal mortality ratio estimate; however, had these deaths been included, the resulting maternal mortality ratio would still be significantly lower than that reported using the standard method.

Conclusion: Relying solely on obstetric codes for identifying maternal deaths appears to be insufficient and can lead to inaccurate maternal mortality ratios. A method enhanced with data matching and record review yields more accurate ratios. Results likely have national implications, because miscoding of obstetric deaths with the standard method may affect the accuracy of other states' maternal mortality ratios

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One issue that makes this difficult to assess is that the U.S. system is highly decentralized. The records are collected at the state and local level, often by a county coroner who is a partisan elected official who is not directly accountable to anyone but the voters and is not necessarily an M.D. (for example, Delta County, Colorado had an EMT with somewhat eccentric views on causes of death as its coroner for a sustained period of time). So, imposing CDC standards is difficult.

Another issue has been deliberately opaque record keeping descriptions in light of the legal and political uncertainties related to reproductive health in the U.S. and in the case of non-citizen mothers, with immigration laws in the U.S.

Home births could be a factor, but given that maternal mortality is rising just as access to health care was often increasing for pregnant mothers at the nationwide level (despite uneven progress) this seems like a less likely explanation.

It is entirely possible that the U.S. data has always been inaccurate but that this was not revealed and disclosed in statistical data until it was examined more carefully by epidemiologists.

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  • I noticed that the link you provided defines pregancy-related death as "the death of a woman while pregnant or within 1 year of the end of pregnancy from any cause related to or aggravated by the pregnancy." That's going to include femicide by father of the baby, FWIW. sanctuaryforfamilies.org/femicide-epidemic
    – shoover
    Mar 2, 2023 at 19:58
  • @shoover It would and that is a leading cause of death for pregnant women. The statistics are further broken down by cause of death.
    – ohwilleke
    Mar 2, 2023 at 20:37
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    So summarizing the second paper in simple language/ for non-native speakers: 'obstetric' is the medical study of pregnancy, childbirth and the few months after birth. The main claim of the paper is that about half of the deaths officially recorded as maternal mortality where of women who were not pregnant.
    – quarague
    Mar 3, 2023 at 7:52
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I don't know how to answer the title question, but you are misinterpreting the spreading green blob in the graph(s). It's not depicting the accuracy of the input data, but the accuracy of WHO's prediction model. And if you read the methodology, there's no "model adjusted data" (blue points) before 2014, i.e. WHO didn't even try to apply any corrections before then. So all this is related to WHO's models rather than input data. Why the WHO chose to apply those corrections is a good question, but probably much better suited to a stack like https://medicalsciences.stackexchange.com/

For the US, the only year for which there's an actual, notable increase in the spread of the blue bars (which is the error for the corrected estimate) is 2021, by the way. It's a sizeable outlier that's driving the green blob to spread. So, the answer is "2021", on a first look.

And on a 2nd look, the WHO combines official data with peer-reviewed studies, i.e. it's meta-analytical. The obvious thing there is that there's [only] one such study for 2021, Hoyert (published: 2022), which reports a PM of 26, much higher than most priors studies, which are in the 13-15 range. So, if you want to further investigate this, read that Hoyert study.

enter image description here

And that Hoyert study seems to be this CDC page which reports

In 2020, 861 women were identified as having died of maternal causes in the United States, compared with 754 in 2019 (3). The maternal mortality rate for 2020 was 23.8 deaths per 100,000 live births compared with a rate of 20.1 in 2019 (Table).

In 2020, the maternal mortality rate for non-Hispanic Black women was 55.3 deaths per 100,000 live births, 2.9 times the rate for non-Hispanic White women (19.1) (Figure 1 and Table). Rates for non-Hispanic Black women were significantly higher than rates for non-Hispanic White and Hispanic women. The increases from 2019 to 2020 for non-Hispanic Black and Hispanic women were significant. The observed increase from 2019 to 2020 for non-Hispanic White women was not significant.

TLDR version: there seems to have been an increase in deaths among minorities in the past couple of years. (The [short] paper doesn't advance/discuss any reasons for that. There's this much longer KFF brief that advances some possible causes, like reduced access to abortion during Covid-19 disparately affecting minorities etc.)

Aside, WHO also reports/include the CVRS data, although only some years in which they decided it's not rendered obsolete by some "specialized study", which (confusingly) however doesn't include Hoyert's.

enter image description here

Anyhow, I don't see a substantive change in how the WHO rated the quality of this data in the past 5 years or so. So the tite question is besides the point; there's no indication of data (as opposed to model) accuracy problem here.

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