(Washington Post illustration; iStock)

Inequality has many roots, but a growing body of research suggests a startling, under-appreciated origin: what happened in the womb.

The idea that prenatal events cast a long shadow over the rest of life is not new; doctors have long counseled pregnant women not to drink or smoke because of the negative health consequences those behaviors can have on children. But in recent years, economists have become fascinated by the possible long-term health impacts of stressful events -- an exploration that began with a focus on famine in pregnancy, but grew to encompass the birth outcomes of being in utero during terrorist attacks, earthquakes, hurricanes and war.

Now, researchers are turning to more commonplace experiences of pregnant mothers -- how the death of a relative, having a home team in the Super Bowl or fasting during Ramadan affects children at birth and beyond. The researchers hope that if they can untangle how mild stress during pregnancy affects the future health of children, it might give them a clue about how more general everyday stress -- such as losing a job or living in poverty -- affects future generations, too.

The hope is that insight, in turn, could help explain whether the stress of poverty is itself a self-perpetuating force -- whether maternal stress is "one channel through which disadvantage is transmitted across generations," as economists Petra Persson and Maya Rossin-Slater write in a new working paper.

Family ruptures and Super Bowl upsets

In their new paper, Persson and Rossin-Slater examined nearly 300,000 births in Sweden between 1973 and 2011, in which a maternal relative died either before a pregnant woman's due date or in her child's first year of life. They found children who were in the womb when a relative died were 25 percent more likely to take medication for ADHD than those who were infants. Those children grew up to be adults who were 13 percent more likely to take prescription drugs for anxiety and 8 percent more likely to take drugs for depression.

Persson, from Stanford University, and Rossin-Slater, from the University of California, Santa Barbara, say that this could have potentially huge financial consequences, even if measured only by expenditures on prescription drugs -- an 8 percent decrease in depression medication spending in the United States, they estimate, could add up to $800 million based on 2008 spending.

The point isn't to make pregnant women paranoid about events they can't control, such as losing loved ones. Instead, they think the data may suggest that women and policymakers should be more attentive to stress during pregnancy, generally, and particularly the chronic stress of poverty, which could be putting kids at a disadvantage before they're even born.

"This would imply that policies aiming to alleviate the stress associated with economic disadvantage may help break the cycle of poverty," Rossin-Slater and Persson wrote in an email.

Another study, forthcoming in the Journal of Human Resources, analyzed birth outcomes in counties where the home team goes to the Super Bowl. Having a team in the Super Bowl isn't what most people would call a major stressor, but that's precisely why it appealed to Hani Mansour at the University of Colorado Denver, and colleagues.

"It's a mild event and that’s part of the design. We think mild events might be more policy-relevant," Mansour said. "More women might be exposed to say, something like a celebration than an earthquake."

The researchers found that women in their first trimester whose home team played in the Super Bowl had measurably different birth outcomes than pregnant women whose teams did not go to the championship. There was a small, 4 percent increase in the probability of having a baby with low birth weight when the team won. The chances of having a low birth weight baby were a bit higher when the team won in an upset, suggesting that surprise may have helped fuel the effect. There was little effect when the team lost.

The magnitude of the change was tiny, but what was striking to Mansour was that it was detectable at all, in studying Super Bowl history from 1969 to 2004. And low birth weight is, in turn, associated with lower earnings and educational consequences.

Inequality: a complex inheritance

There's a huge caveat to interpreting these studies. It's fascinating to discern patterns, such as a risk of cardiovascular health, diabetes, or even future earnings potential that appear to be shaped by experiences in the womb. But these studies are not experiments; after all, it would never be ethical to randomly separate pregnant women into two groups and subject some to stress, famine, or family tragedies and some not. That means researchers have to use natural experiments and existing data sets to explore their hypothesis. That leads to imaginative studies -- like the Super Bowl one -- but also means that they can't be certain that it's the prenatal experiences and not some other factor that explains the result.

But the motivation for these studies is a clear policy question: When can we most effectively intervene? Economists know that inequality is a complex inheritance, influenced by the neighborhoods where we live, the schools we attend and how we're raised, among many other factors. But there are growing questions about whether it starts even earlier.

"I think it’s coming at the heart of the question about inequality," Mansour said. "It’s not something that’s sprung up on us when we’re 18. ... The point is, inequality doesn’t just come up at some point -- for many people it starts at birth."

But that points to one last reason these less extreme events are of interest to economists. Many of the studies of prenatal shocks involve catastrophic or world-changing events. Those events come with other effects that may also contribute to any differences in babies' short- or long-term health, because they may increase pollution in the environment, cut off income, or make medical care inaccessible as societal infrastructure must be rebuilt from scratch. The milder events are more similar to the kinds of stressors that pregnant women face everyday and also don't often disrupt their daily routines so much that they instill other changes that could account for any differences.

Insulating pregnant women from normal and unavoidable situations like the death of a loved one or the Super Bowl is not practical or what either group has in mind. But the researchers think that the accumulating evidence that stress is associated with negative outcomes may spark a deeper consideration of avoidable stresses that could leave a deep imprint on future generations.

Meanwhile, researchers are continuing to try and answer the biggest question lurking behind all these fascinating patterns -- to understand the biology that could explain some of these findings.

More from Wonkblog:

The rules about who should get a C-section could be all wrong

Today's moms are working later into their pregnancies — and going back to work earlier, too

It's a retirement account, but for pregnancy