In late May 2008, across the state of Iowa, something weird started happening to newborns. For the next nine or so months, more babies across the state were born underweight, compared to the same period of previous years.

Not just any babies, though. There was no difference among babies born to white mothers. Infants born to Latina mothers, however, faced a 24% higher risk of entering the world smaller than they should have been.

What accounted for the difference? One compelling hypothesis to this puzzle, proposed in a study published (paywall) last year in the International Journal of Epidemiology, may help us anticipate the hidden, long-term toll on Americans’ health resulting from the brutal methods of US president Donald Trump’s immigration policies.

The ripple effects of stress

This wasn’t precisely a massive public health crisis. In absolute terms, the freak increase in Iowan infants born “low birth weight”—less than 5.5 pounds (2,499 grams)—translated to only a couple-dozen babies being born a few ounces lighter than normal.

But those lost ounces matter a lot in those first days of life. Underweight babies face higher risk of death in infancy, as well as of long-term health and academic problems.

The odd pattern also offered clues to a larger health phenomenon among Iowa’s Latino residents.

Babies are born too small when conditions in utero make it hard for them to grow. That includes high levels of stress hormones flowing from the mother’s body into the placenta. Like studying rings on a tree for signs of unduly harsh weather conditions, comparing the health of newborns born at different times, to similar women, offers an unusually precise way of gauging maternal stress at a certain point in time. And to the study’s authors, that time frame was clear: the risk of underweight babies born to Latinas was higher in the nine months after May 2008 than any other time between 2003 and 2013.

So what happened in May 2008 that might have stressed out pregnant Latinas across the state? The study’s authors point to the events that occurred that month in Postville, a tiny hamlet in the state’s northeast, where the US Immigration and Customs Enforcement (ICE) launched one of the largest federal worksite immigration raids in American history.

The Postville raids

On the morning of May 12, two Black Hawk helicopters thrummed in the sky overhead as some 900 federal officers in SWAT gear tumbled from black SUVs, storming the factory floor of was at that time the world’s biggest processor of kosher meat. US immigration forces cuffed the 389 workers, linked them by chains at the waist, and packed them into white buses with blacked-out windows. All but a few of the workers were Latino, most of them from two small towns in Guatemala. State and local media heavily covered the raid, as well as the ensuing terror that swept the tiny town in the days that followed—including young children left alone for up to 72 hours after their parents were arrested and panicked families seeking refuge in the local Catholic church.

The ICE raid affected Latinas on the basis of their identity alone.

Most of the Latinas across Iowa who gave birth to underweight babies in the months that followed weren’t directly connected to the Postville crackdown. What’s more, many faced no threat of deportation whatsoever, since they were US citizens. And yet some still experienced stress intense enough to stunt their babies’ growth, after controlling for maternal age, smoking habits, and other factors. This suggests that the ICE raid affected Latinas on the basis of their identity alone, says Arline Geronimus, a professor of public health at the University of Michigan who co-authored the study.

How might that happen? Consider the range of upsetting accounts and images that lit up TVs and social media in the weeks and months that followed.

The use of helicopters and SWAT gear, and the parades of shackled workers, cast Latinos as dangerous criminals—even though nearly all of the workers pled guilty to nothing more egregious than working under fake Social Security numbers used to pay taxes, which the plant’s owner had facilitated. Despite the pedestrian nature of the violations, the follow-through was as aggressive as the raid had been. Instead of being deported directly, as was the norm at the time, around 270 of the Agriprocessors workers, many of them breadwinners, were sent to prison for five months first.

Some Latinos in the area undoubtedly faced fears of violent, highly public arrest and detention in possible follow-up ICE raids. Spanish-language newspapers spread distressing eyewitness accounts and frightening images from Postville throughout other Latino communities in Iowa, many of them also built around agricultural plants. Rumors of impending raids and ICE going door to door roiled Latino communities throughout the state.

The ICE raids could have led to heightened economic fears on the part of the Latino community, too, as employers declined to hire Latinos lest their workforce’s ethnic makeup attracted ICE’s attention.

“When you think about that kind of massive stress response owing just to your identity—that’s pretty powerful.”

Then there’s the social stigma to consider. In the flurry of coverage, local media aired man-on-the-street comments about the Postville operation featured plenty of hostility not just toward migrants working illegally, but also toward “all the Mexicans” and casual speakers of Spanish. These included remarks like: “I don’t enjoy going to the grocery store or to the malls and all I am hearing half the time is spanish [sic] talk” and ”Those of you waiving [sic] the Mexican flag and proclaiming your unhappiness with the United States: Go there, live by their rules!”

That toxic confluence of factors likely made Latino communities feel more vulnerable, says Geronimus. “After this kind of raid there would also be the psychosocial impact of fear, anxiety, and depression,” she says. “When you think about that kind of massive stress response owing just to your identity—that’s pretty powerful.”

And though the research revealed these effects through the impact on newborns, it’s unlikely the Postville episode only affected pregnant Latinas. “Pregnancy is kind of a window—a concrete tangible measure —into what some of these frightening policies can do to people’s health,” says Geronimus, adding that other Latinos in Iowa likely suffered similar, though harder to measure, levels of stress.

The weathering hypothesis

Postville was the last massive, militarized workplace crackdown on immigrants for the next few years—until 2017, when Donald Trump took office.

Last year, ICE launched an aggressive new campaign of large-scale worksite raids. Targets so far include 7-Eleven stores, restaurants, suburban gardening centers, and meat-processing plants. Around 750 people have been arrested on the job so far this year, based on media reports (including, as it happens, 32 Latino men at a concrete factory in Postville).

Those operations have taken place alongside Trump’s policy of separating children from their parents at the US-Mexico border, which he put on hold in June only after the upsetting footage sparked public outrage.

Both policies explicitly aim to deter migration through fear. The propagandist benefit of these scare tactics is that their paramilitary intensity makes the targets seem like dangerous criminals, not lowly meat processors. That, alongside Trump’s exaggeration of the threat of criminal gangs like MS-13, feeds a stereotype: Anyone who looks like the people being publicly targeted in raids must be breaking the law.

Many Americans shrug off the undue cruelty of Trump’s immigration policies—as opposed to the norm for most of the past 15 years, arresting and deporting without the militarized fanfare—as the price individuals pay for breaking the law. But if the case of the Iowan babies is anything to go by, their fellow law-abiding Americans are suffering the toll too, says Geronimus.

This relates to the “weathering hypothesis,” which Geronimus began pioneering back in 1992. That hypothesis holds that cumulative exposure to discrimination and disadvantage erodes people’s health.

This phenomenon is hard to quantify because the effects are often complex and unfold over decades.The Postville raid offered a rare chance to measure what was essentially a natural experiment. That said, signs of a broader physiological impact of immigration crackdowns on Latinos turned up in another Geronimus study, this one published in the Journal of Health and Social Behavior in 2016. The study looked at different ethnic groups and socioeconomic classes in Detroit, analyzing the length of subjects’ telomeres—the protective caps on the ends of chromosomes, the shortening of which may indicate aging caused by stress.

Though she and her co-authors did not emphasize this point in their paper, Geronimus found that among Latino residents, the frequency of respondents’ worries about safety in their home or neighborhood was particularly associated with shortened telomeres. When they shared this unexpected finding with the community-based group with whom they partnered to conduct the study, the partners mentioned that data collection coincided with a period of heightened immigration enforcement.

The research is a reminder that while Trump’s “law and order” is likely costing Latino-Americans dearly, other residents pay a lesser price. Take, for instance, Sholom Rubashkin, the Agriprocessors CEO, who in 2009 was convicted of 86 counts of federal bank fraud. Due to the 27-year prison term given for his financial crimes, the charges of immigration and child labor violations documented in the 2008 Postville raid were dropped. But in December 2017, Rubashkin walked free. Trump had commuted his sentence.