Prenatal Stress Promotes the Development of Sensitivity

Background information

Prenatal stress is often viewed as a solely negative experience with numerous studies linking it to adverse child outcomes such as increased mental and physical problems.

Counter to this traditional viewpoint, Pluess and Belsky (1) proposed that prenatal stress enhances developmental plasticity, meaning that prenatal stress increases a child’s sensitivity to both positive and negative aspects of their postnatal environment.

Thus, this theory suggests that a prenatally-stressed child raised in a supportive environment would go on to display more positive functioning, such as greater social competence and less problem behaviour, but if raised in a stressful environment would develop greater problematic behaviour and lower social functioning.

Testing this theory can be difficult because the quality of the prenatal environment is often closely related to the one after birth.

Take, for instance, a pregnant mother under large amounts of stress due to factors such as poverty, an unstable relationship, or mental illness. Those same factors causing stress in the prenatal period are very likely to continue after the baby is born.

Thus, we may observe that prenatally-stressed children are more sensitive to adverse postnatal environments but not as easily determine whether they are more sensitive to positive ones.

Our study

Therefore, to test the theory of whether prenatal stress increases developmental plasticity, we decided to use an animal model in which we could control the quality of both the prenatal and postnatal environment (2).

We chose to use prairie voles because, unlike other common rodent models, they are bi-parental (both mother and father raise pups) and form social bonds which is more similar to humans.

Study design

For the experiment, pregnant voles were assigned to either a stress- or no-stress-condition. After pups were born, they were cross-fostered (switched to unrelated parents) and raised by parents known to either display high levels of parental care (positive environment) or low levels of parental care (negative environment).

Thus, there were four groups: 1) prenatally-stressed and high-parental care, 2) prenatally-stressed and low-parental care, 3) not-prenatally-stressed and high-parental care, and 4) not-prenatally-stressed and low-parental care.

Once the voles were adults, we tested them on a number of outcomes including anxious behaviour and stress reactivity.

Main findings

Results showed that prenatally-stressed voles raised with high-parental care had the lowest levels of anxious behaviour and stress reactivity.

However, if they were raised with low-parental care they had the highest levels of anxious behaviour and stress reactivity.

For voles that did not experience prenatal stress, the quality of parenting that they received did not predict their adult behaviour. In other words, they were not as sensitive to their postnatal environment.

Thus, the study supported the hypothesis that prenatal stress increases developmental plasticity.

General conclusion

Clearly more work needs to be done before we can say the same processes are occurring in humans.

However, this work suggests that prenatal stress may not be “all bad” but instead sensitizes children to both positive and negative aspects of their environment after birth.

If this were true, it would indicate that early interventions targeted at families experiencing high levels of stress during pregnancy may be especially effective at promoting child well-being.