Prenatal Stress and Cognitive Function: A Natural Experiment

It is well-documented that stress can jeopardize prenatal development. In fact, past studies have found a negative correlation between the amount of stress a mother experiences during pregnancy and the future cognitive abilities of her child. Since a child’s cognitive abilities can heavily influence his or her life outcomes, it is crucial that researchers understand the underlying mechanisms driving this association. However, because there are many factors—from shared genes to family wealth—that are correlated with both maternal stress and academic success, it is difficult to assess cause and effect without a randomized controlled trial. In other words, in order to determine causation with regard to prenatal stress, a researcher would need to set up an experiment in which he or she randomly assigned life stressors to pregnant women. Of course, this experimental design is neither ethical nor feasible, so the connection has gone unexplored.

In a recent study, researcher Florencia Torche attempted to evade this obstacle by identifying the closest thing possible to the random assignment of stress: a natural disaster. She used a 2005 earthquake in Chile to represent a stressful event that affected some parts of the country more severely than others. Since this event was unpredictable and affected families across a wide variety of locations and income levels, the earthquake essentially acted as a mechanism to randomly assign a group to a major stressor. Torche identified mothers who were in their first trimester of pregnancy during the earthquake and compared two groups: 558 women in a region that barely felt the impact of the earthquake, and 591 in the area that experienced the most severe shock. Then, she measured the cognitive function of these mothers’ children by performing a series of tests from the Wechsler Intelligence Scale about seven years after their births.

When Torche first analyzed the data, she found no significant difference between the cognitive function of the children in the two groups. However, when she grouped the mothers by socioeconomic status, a compelling pattern emerged. Torche identified the mothers by their highest level of education and sorted them into three groups: those with less than a high school diploma, those who had a high school diploma, and those who had some college. In the group that had not finished high school, children from the region with the highest earthquake impact showed significantly lower cognitive outcomes than those from the region that experienced little impact. This was the only socioeconomic group that showed a significant difference between the two regions. In other words, while all of the mothers had experienced prenatal stress, only the children of the least-educated mothers showed a significant long-term negative effect.

In her analysis, Torche considered a few different explanations for this finding. She proposed that the socioeconomic differences could have aligned with varied levels of exposure to the earthquake’s effects or differing levels of sensitivity to the stress. However, Torche ultimately attributed the pattern to differences in parental responses to their children’s behavior. She suggested that well-educated and advantaged parents might observe the effects of prenatal stress on their children and use their resources to compensate. For example, these parents might have spent more time reading with their children or hired a professional psychologist for support. On the other hand, perhaps poor and less-educated parents may not have been able to compensate for their children’s disadvantage, as their resources were limited.

The results of this study suggest that prenatal stress can indeed have adverse effects on children that might impact their future life outcomes, particularly in disadvantaged families. Policymakers who shape women’s health services should consider the implications of Torche’s study while reflecting on the long-term impacts of those programs in low-income communities.

Article source: Torche, Florencia. “Prenatal Exposure to an Acute Stressor and Children’s Cognitive Outcomes.” Demography 55, no. 5 (2018): 1611-1639.

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