Race Leading SDOH in Maternal Health Disparities Beyond Income

March 28, 2023 - Pregnant individuals with low incomes typically have higher rates of maternal and infant mortality compared to those with higher incomes. However, according to a study out of Michigan Medicine, Black birthing people do not experience the same advantage, indicating that race holds more weight as a social determinant of health (SDOH) than income in influencing maternal health outcomes.

The study, published in the National Bureau of Economic Research, analyzed almost all infants born to first-time mothers in California between 2007 and 2016. Researchers utilized a combination of California birth records, hospitalizations, and death records, as well as parental income data from the Internal Revenue Service tax records and the Longitudinal Employer-Household Dynamics file to understand infant and maternal health inequity further.

Despite being one of the wealthiest nations globally, the United States lags behind other countries in terms of infant and maternal health indicators, Sarah Miller, PhD, one of the study’s authors and an associate professor at the Ross School of Business, said in a public statement.

This observation comes amid alarming maternal mortality rates in the US. In 2022, the Commonwealth Fund found that the US has one of the worst maternal mortality rates in the developed world. Pregnant people in the US face over twice the risk of dying from childbirth or pregnancy-related complications compared to women in other OECD countries.

“There have been a lot of papers and analysis showing that if you compare the US to other wealthy countries, we do quite poorly in terms of infant and maternal health,” Miller said. “And there's a lot more inequality, particularly race-based, in the US than in other countries. Income is potentially a really important factor in this, but it's been hard to nail that down because birth certificate data doesn't have any information on family income.”

READ MORE: Maternal Health Disparities Need Data-Driven, Community-Based Approach

“What we're bringing to the table is this new dataset, which links birth certificates to income data so we can actually see how rich families’ kids and moms are doing compared to poor families’, and how that interacts with other disparities like race,” Miller explained.

Unveiling an unexpected finding, the study showcased that infants born to the wealthiest 20 percent of families have poorer health outcomes than those from the lowest income bracket. These babies from the top 20 percent face a higher likelihood of being born premature and with a low birth weight—15 percent and 27 percent higher, respectively—increasing their risk for early medical complications.

The researchers posited that age could have factored into that finding.

“Higher-income women were having their first birth at an older age, or those that had their first births at an older age were higher income,” Miller explained. “And the fact that they had more multiple births suggests that maybe there was some fertility assistance that was responsible.”

“The thing that we found really interesting was that although we found much higher rates of preterm and low birth weights among the very wealthiest families, they also had the very lowest infant mortality,” Miller said. “So even though babies were being born with these very high-risk factors at very high rates, they were also the most protected.”

Miller highlighted that the pattern of poorer babies having better health outcomes shifts when examining infant mortality, the most severe indicator of infant health. Infants born to families with the highest income have mortality rates half those in the lowest income group, with 1.8 deaths per 1,000 births compared to 3.7 deaths per 1,000 births, respectively.

Additionally, the maternal mortality risk for impoverished mothers was three times higher, even when treated in the same hospitals. Past studies have shown similar findings; even within the same hospitals, Black patients were more likely than White patients to experience adverse patient safety events, highlighting racial health disparities.

While the impacts of race and maternal health outcomes are well known, the researchers were curious whether this effect would vanish among the wealthiest Black families.

Theoretically, Black families should have equal access to premium healthcare that White families receive for their children. However, the study discovered that although higher income does improve maternal and infant health over time, it isn’t enough to counteract the effects of race.

The findings showed that babies born to non-Hispanic Black mothers experience the worst health outcomes across all income levels.

For Black women, preterm birth rates ranged from 11.5 percent to 14.6 percent, and low birth weight rates varied between 10.9 percent and 14.3 percent. In comparison, preterm birth rates range from 8.1 percent to 11.3 percent for non-Hispanic White mothers. Low birth weight rates range from 6.2 percent and 9.7 percent for that same racial group.

Miller noted that the research could not identify a specific reason for these disparities.

“These patterns don't seem to go away if we account for hospital quality, age, or multiple births,” Miller said. “We can't pin down a specific cause. That's definitely for future work.”

Miller emphasized that the research highlights that interventions focused on improving infant and maternal health in the United States should also focus on racial groups rather than being exclusively focused on low-income families, as has been the case in the past.

"There was hope that targeting low-income individuals would close racial gaps. However, achieving that goal solely through this approach will be challenging,” she expressed.