A study of nearly 1,900 fatal police encounters and millions of birth records in California suggests that police killings of unarmed black people may affect the health of black infants before they are even born.

Pregnant black women who lived near the site of such officer-involved fatalities had their babies sooner than mothers who weren’t exposed to such incidents during their pregnancies, researchers found. What’s more, those infants had significantly lower birth weights — a risk factor for future health problems.

The findings, published this week in the journal Science Advances, point to the ways police killings of unarmed black Americans affect the community at large, even over multiple generations.

“We often think about police violence as having these individual-level consequences,” said Kristin Turney, a sociologist at UC Irvine who was not involved in the new research. “But this paper is really innovative because it shows that police violence has spillover effects. … It can affect people even in utero.”


In the wake of the well-publicized police killings of Michael Brown, Eric Garner, Freddie Gray, Tamir Rice and many others, scientists have begun to explore how such violence ripples beyond the original victim. For example, a 2018 study in the Lancet linked police killings of unarmed black men with an increase in mental health problems for black people living in the same state.

Joscha Legewie, a sociologist at Harvard University, has studied the ways that aggressive policing can lead to poor academic performance. He collaborated on a study this year in the American Sociological Review that linked aggressive policing surges by the New York Police Department to poorer test scores for the African American students in the areas the police targeted. He also knew that many of the health disparities black children face start even earlier — beginning at birth, if not sooner.

Children born with a low birth weight — defined as anything under 2,500 grams, or about 5.5 pounds — are at greater risk for learning disabilities, delayed motor and social development and other health problems, according to the Centers for Disease Control and Prevention. In the United States, the risk of low birth weight is nearly twice as high for black infants as it is for white and Latino infants, according to the March of Dimes.


Legewie wanted to see whether living with the threat of police violence could be a contributing factor.

To probe this question, he examined 3.9 million California birth records from 2007 to 2016, including more than 246,000 for black infants. The detailed records allowed him to extract health data about the babies as well as information about where their mothers lived.

He combined this data with records from the Fatal Encounters database, a journalist-led system that collects publicly available information on police violence. A total of 1,891 officer-involved killings were included in the analysis, all of them occurring in California between 2005 and 2017; 164 of those cases centered on unarmed black victims.


Legewie discovered that when an unarmed black person was killed within a kilometer of a black woman’s home during the first or second trimester of pregnancy, her infant’s birth weight was significantly lower compared with black mothers who were not exposed to such events. The difference ranged from 50 to more than 80 grams, depending in part on how far along the pregnancy was at the time of the killing. (No link was seen in the third trimester.)

There was no link between birth weights and police killings of black people who had been carrying weapons, Legewie found. Moreover, police killings of either armed or unarmed whites and Latinos did not have a significant effect on the birth weights of white or Latino infants, respectively.

“This finding indicates that the effect is race specific and driven by perceptions of discrimination and structural racism instead of general threats of crime and violence,” he wrote in the paper.

Legewie repeated the analysis multiple ways to double-check the results. He compared the results between women who experienced these nearby episodes of police violence during pregnancy to women who experienced it after their babies were born. Only exposure during pregnancy was linked to low birth weight, he found.


To control for differences among mothers, he also focused on black women who experienced these events during one pregnancy but not others. Again, infants born after a nearby police killing of an unarmed black person had lower birth weights, but their siblings did not.

In his analysis, he also made sure to control for other confounding factors, such as the general level of poverty and other violence in the area.

No matter how he analyzed it, the results still held.

“This is an important finding and a very intuitive one,” said Amanda Geller, a sociologist at New York University who was not involved in the work. “The fact that it is so clear and so clearly, methodologically, rigorously documented is really important.”


Evidence has mounted that young men, particularly young black men, are more vulnerable to violent police encounters. For instance, a study published in August in the Proceedings of the National Academy of Sciences found that black boys and men were 2.5 times as likely to be killed by police as their white counterparts.

But the new findings suggest that the effects of police violence can influence black children before they’ve had a chance to encounter law enforcement.

While Legewie did not study the physiological mechanisms that might be at play, he said it’s likely that the stress experienced by the pregnant women as a result of these violent events was affecting the birth weight of their children.


Geller agreed.

A mother’s proximity to a police killing, she said, “could potentially hammer home what it means to be raising a black child in America.”

Ultimately, the findings point to the need to treat police violence as a public health issue — one that should be addressed by doctors and institutions treating or assisting black mothers-to-be, said Florencia Torche, a sociologist at Stanford University.

“Providing easy access to support and assistance to try to compensate for the potential negative effects of this type of exposure is good social policy,” said Torche, who was not involved in the study. “It supports the health and well-being not only of the current generation of adults who are exposed, but also of the next generation.”


The next step, researchers said, would be to further explore exactly what physiological stress mechanisms were at work within the bodies of pregnant women — and perhaps to see how these effects manifest in birth record data from other states.