The study has been published online in the journal Biological Psychiatry.
"Our results shape the argument that fetal exposure to cortisol - which may in part be controlled by the mother's stress level - and early caregiving experience combine to influence a child's neurodevelopment," said study author Thomas O'Connor, Ph.D., professor of Psychiatry and of Psychology at the University of Rochester Medical Center, and director of the Wynne Center for Family Research. "If future studies confirm these findings, we'll need to not only engineer ways to reduce stress in pregnancy, but we'll need to also promote sensitive caregiving by moms and dads."
To reach the conclusion, researchers recruited 125 women at an amniocentesis clinic in an urban maternity hospital, taking a sample of their amniotic fluid so that stress hormones in it could be measured. The mothers were at 17 weeks gestation on average; only mothers with normal, healthy pregnancies and subsequent deliveries were followed.
When their children reached 17 months of age, researchers administered a Bayley infant developmental scale test, which relies on puzzles, pretend play, and baby "memory" challenges to gauge youngsters' cognitive development. They also observed the baby and mother using the Ainsworth "Strange Situation" test, which judges childrearing quality, categorizing mom-baby pairs as either showing secure or insecure attachment to each other.
With cortisol levels, relationship quality results, and cognition scores in hand, researchers analyzed how the first two measures might influence the third. Indeed, for children showing "insecure attachment" to their mothers, a high prenatal cortisol level was linked with shorter attention spans and weaker language and problem-solving skills. But interestingly, for kids who enjoyed secure relationships with their moms, any negative link between high prenatal cortisol exposure and kids' cognitive development was eliminated.
"This is such refreshing news for mothers," O'Connor said. "Pregnancy is an emotional experience for many women, and there is already so much for mothers to be careful of and concerned about. It's a relief to learn that, by being good parents, they might 'buffer' their babies against potential setbacks."