Stress in utero harms cognitive skills of poor children

A young girl walks through the streets past homes damaged by the February 27 earthquake on March 13, 2010 in San Pedro De Alcantara, Chile. (Credit: Joe Raedle/Getty Images)

Exposure to an acute stress in utero can have long-term consequences extending into childhood—but only among children in poor households, according to a new study.

The study, which took place in Chile, did not find the same effect among children in upper- or middle-class families.

“These children performed worse on a diverse set of skills critical for educational success, including arithmetic reasoning, verbal fluency, spatial analysis, logical thinking and problem-solving skills,” says study leader Florencia Torche, sociology professor in the Stanford University School of Humanities and Sciences.

Torche also found that while middle- and upper-class families have the resources to mitigate the effects from the event, disadvantaged children without extra help can fall up to half a year behind, according to the research in Demography.

The ability to catch up depends on the family’s socioeconomic resources, she finds.

“This is a troubling finding because it shows that acute stress exacerbates disadvantages that poor children already face,” Torche says.

Stress doesn’t occur on its own

While previous research has examined the effects of chronic stress, little is known about the long-term consequences of an acutely stressful event during pregnancy, says Torche. An acute stress a pregnant woman could experience include witnessing a violent event, falling victim to a crime, almost suffering a serious injury, or losing a job.

But because stress is often correlated with other challenging situations—like family turmoil, relationship difficulties, or financial problems—it can be difficult to study, says Torche. That’s why she used a disaster event to create a natural experiment: a 7.9 magnitude earthquake that occurred June 13, 2005, in Tarapaca, Chile.

“If we want to disentangle the effect of stress from these other common correlates, we need to isolate it,” Torche says.

“It was only when I broke the results down by socioeconomic status that I found a very strong negative effect among the most disadvantaged families.”

Unlike most natural disasters with devastating consequences—such as property damage, long-term displacement, or public health emergencies—the losses from the Tarapaca earthquake were relatively small: 11 people died, 130 were injured, and 180 homes were destroyed. With limited spillover effects that could have influenced health outcomes of a mother and her unborn child, Torche was able to more clearly isolate the direct impact of an acute stress on pregnant women.

Torche then combined birth records with a random sample of 591 children whose mothers experienced the earthquake during their pregnancy and compared that data with a control group of 558 randomly selected children born in the same time period in Chilean counties the earthquake didn’t affect.

Torche has closely studied these children since birth. Her 2011 study found that exposure to an acute stress during pregnancy increased the number of preterm births.

“Given that preterm birth is associated with health and developmental problems during childhood, this finding provided initial evidence that prenatal exposure to acute stress could have negative consequences for children,” she says.

Half a year behind

Here, Torche checked in with these children who were now 7 years old and starting school.

With a team of trained field researchers, Torche conducted a series of cognitive tests with each child in the treatment and control groups.

“The effect of prenatal exposure to an acute stressor emerged only among the most disadvantaged members of society.”

They assessed abilities such as verbal comprehension, spatial reasoning, memory, and how quickly children processed information needed to perform a task.

At first, Torche found no statistically significant effects when she looked at the results for the entire sample. But as she dug deeper into the data, she made a striking discovery: only the children from poor households showed negative effects. There was no effect on children from middle- and upper-class families.

“It was only when I broke the results down by socioeconomic status that I found a very strong negative effect among the most disadvantaged families,” she says.

Torche then broke it down even further. Because poor children face a range of educational disparities, how did disadvantaged children who experienced the earthquake compare to poor children in the control group who did not?

Torche found a difference that amounted to more than half a year of cognitive development. In other words, a low-income child in the second grade who experienced stress in utero was performing closer to a first-grade level.

Access to resources

After establishing an unequal effect of stress, Torche conducted a set of qualitative interviews to understand why children from middle- and upper-class families were unaffected. At the time of these interviews, the children were mostly 9 years old and in fourth grade.

In their interviews, upper- and middle-class parents shared that they constantly assessed their children’s strengths and weaknesses. If a child showed signs of struggling in any way, they mobilized resources to intervene. This included hiring tutors, signing up for structured activities, and interacting more with teachers and the school to help their child inside and outside of the classroom.

Racial health disparities start early in life

“While some disadvantaged families have also resorted to the assistance of experts and educators, and have requested institutional support, they face substantial barriers in terms of time, economic resources, and, equally important, access to social networks and mastery of cultural resources to effectively negotiate with institutions for advantages for their children,” Torche writes in the paper.

Torche notes that this finding shows that class-based parental responses that minimized effects of prenatal stress could further exacerbate social class disparities.

This research is yet another piece of evidence that shows the importance of supporting disadvantaged women and their children, Torche says.

“The effect of prenatal exposure to an acute stressor emerged only among the most disadvantaged members of society. Given that these women are particularly vulnerable, and less likely to have access to health care, increasing access to health care and sources of support for this population is an important task,” she says.

Source: Stanford University