The gap didn't hold steady. It widened.
Among the 380,000 births tracked across the United States between 2012 and 2022, a pattern emerges that is both familiar and newly alarming: the poorer a mother's household, the worse her baby's chances at a healthy start. A study published in JAMA Pediatrics has put hard numbers to what many clinicians have long suspected, and one of those numbers has researchers particularly worried.
The rate of low birthweight among lower-income mothers climbed from 7.2% in 2012 to 9.4% in 2022 — a jump of more than two percentage points over a decade. Among higher-income mothers, the same figure crept from 5.7% to 6.3%. The gap, in other words, did not hold steady. It widened. And that widening, researchers say, was driven almost entirely by worsening outcomes among families already struggling.
About 37% of the mothers in the study were classified as lower-income, defined as living below 200% of the federal poverty level. Across nearly every measure of newborn health — preterm birth rates, average birthweight, length of pregnancy — these women fared worse than their higher-income counterparts. The consistency of that gap across all ten years of data is striking on its own. The acceleration of the low-birthweight disparity makes it more urgent.
Emily Dore, a postdoctoral fellow at Harvard T.H. Chan School of Public Health and the study's lead author, called the growing gap in low birthweight both surprising and especially concerning. The increase, she noted, was not a broad societal trend pulling all families in the same direction — it was concentrated among those with the least financial cushion.
Megan Reynolds, a sociologist at the University of Utah and a coauthor of the study, offered a framework for understanding why. By the time a pregnant woman walks into a doctor's office, she has already been shaped by everything outside it — the stability of her housing, whether she had enough to eat, the chronic low-grade stress of financial precarity. That stress, Reynolds argues, is not metaphorical. It is physiological. It gets under the skin, she says, and causes the body to malfunction. Health care, in her view, explains only a small fraction of health disparities. The rest lives in the conditions of daily life.
Preterm birth — delivery before 37 completed weeks of pregnancy — is one of the leading causes of infant illness and death in the United States. Babies born early and underweight carry elevated risks of serious health complications, developmental delays, and challenges that can persist across a lifetime. Knowing whether those rates are rising or falling, and for whom, requires consistent, long-term data collection.
The researchers drew their data from the CDC's Pregnancy Risk Assessment Monitoring System, known as PRAMS, a national survey that has tracked maternal and infant health since the 1980s. Reynolds described it as a treasure — one of the only datasets that captures not just what happens at birth, but the full circumstances surrounding it. That makes a recent development particularly troubling: in the spring of 2025, the CDC's PRAMS office was shuttered indefinitely, leaving the program's future uncertain.
The authors are explicit about what they hope the research accomplishes. They want policymakers to treat social policy as health policy — to recognize that income support, food assistance, and anti-poverty programs are not peripheral to maternal and infant health but central to it. The generosity of those safety nets varies considerably from state to state, and the study suggests that in many places, they are not doing enough.
Daniel Collin and Rita Hamad of the Harvard School of Public Health also contributed to the research, which was supported by grants from the National Institutes of Health. The question now is whether the data infrastructure needed to track these trends — and the political will to act on them — will survive long enough to matter.
Notable Quotes
Worrying about housing, food access — the stress from financial hardship gets under the skin and causes the body to malfunction. Health care only explains a small share of health disparities.— Megan Reynolds, sociologist at the University of Utah and coauthor
The growing gap in low birthweight was surprising and especially concerning, particularly because it was largely driven by increasing rates among lower-income families.— Emily Dore, postdoctoral fellow at Harvard T.H. Chan School of Public Health and lead author
The Hearth Conversation Another angle on the story
What's the core finding here that separates this study from general knowledge that poverty affects health?
It's the trajectory. We already knew lower-income mothers had worse outcomes. What this shows is that the gap in low birthweight specifically got larger over ten years — and the movement came from the bottom, not the top.
Why does low birthweight matter so much as a metric?
It's a signal that travels far into a child's life. Babies born underweight face higher risks of developmental delays, serious illness, and long-term health challenges. It's not just a number at birth — it's a forecast.
The researchers keep pointing away from health care as the explanation. What are they pointing toward instead?
The conditions before the clinic visit. Housing instability, food insecurity, the chronic stress of not having enough — these shape a body long before any doctor is involved. Reynolds calls it stress getting under the skin and causing the body to malfunction.
Is there a policy mechanism that actually addresses that?
The study points to income support and food assistance as partial buffers. But the researchers are careful to note that how much those programs help depends heavily on which state you're in. The safety net is uneven.
What's the significance of the PRAMS database being shut down?
It's the only national system that captures both what happens at birth and the social circumstances surrounding it. Without it, researchers lose the ability to track whether things are getting better or worse — and for whom. The study itself is an argument for why that data matters.
So the research is partly making a case for its own data source?
Implicitly, yes. Publishing findings from PRAMS right as PRAMS is being shuttered is not a coincidence. It's a demonstration of what disappears when the infrastructure disappears.
What would it actually look like to treat social policy as health policy?
It would mean evaluating anti-poverty programs partly by their effect on birth outcomes. It would mean a housing subsidy or a food benefit showing up in a pediatric health conversation. The researchers want that boundary to dissolve.