This is an interesting piece in general about some ways that charts can be misleading, but I was most struck by this particular example — it’s seemed worrying to me that US maternal mortality rates have risen in the past 25 years, and this seems like fairly strong evidence that it actually hasn’t.
But even when no one is intentionally trying to mislead or manipulate, charts designed to make information clear can still lead to erroneous conclusions. Just consider the U.S. maternal mortality statistics, which seem to show maternal deaths rising from 0.4 deaths per 100,000 women in 2003 to close to 1 per 100,000 in 2020.
Maternal mortality rates over time, with zoomed version at bottom. Note that the uptick in maternal death rates is limited to the U.S. Credit: Our World in Data
This graph is worrisome, particularly if you or your partner is pregnant (or expect to be). Why are so many more expectant and new mothers dying? Is there some new danger? Is the healthcare system getting worse? Coverage in Scientific American, NPR, and elsewhere suggested that the answer to these questions was “yes.”
In May 2024, however, Saloni Dattani reported in Our World in Data that the purported increase in U.S. maternal mortality stems mostly from changes in how these deaths are counted. Before 1994, the International Classification of Diseases (ICD) defined a “maternal death” as one where pregnancy is listed as the underlying cause of death on the death certificate. However, this led to many maternal deaths not being counted, including cases wherein the underlying cause of death was a condition that is exacerbated by pregnancy.
When the ICD was updated in 1994, the definition was expanded to include deaths from “any cause related to or aggravated by the pregnancy or its management.” The ICD also recommended “pregnancy checkboxes” on death certificates to help doctors catch more pregnancy-related deaths.
Dattani shows that as U.S. states gradually introduced the pregnancy checkbox and implemented the new ICD definition, rates of maternal death appeared to rise. So, it seems that the upward trend in the graph doesn’t come from changes in the actual death rate but from changes in what counts as a maternal death, to begin with. None of this is indicated in the charts, which plot smooth lines without any gaps or discontinuities.
