O'Connor goes on to note a couple important nuances of the study. The first is that the amniotic (in-utero) cortisol studied could result from two sources, and it's hard to pinpoint which. It might, for instance, be passed along the placenta from an anxious mother to her unborn baby - or it could be created and excreted directly by a stressed fetus itself.

"While many large-scale studies have observed that prenatal stress may influence child development, our particular study sheds some light on the 'how'," O'Connor said. "Still, much more research is needed to better pinpoint the exact mechanisms behind a mother 'transferring' her stress to her unborn baby."

This study plays into the much larger theory of "fetal programming," which suggests that events in the womb may prime the developing child for long-term health and developmental outcomes. Past studies, for instance, have found a pregnant mother's diet can sway a child's long-term risk for heart disease, diabetes and obesity. Along with diet, prenatal stress has emerged as another large-looming factor in such programming.

"Our results support this emerging theory," said London-based study co-author, Vivette Glover, Ph.D. "In neurology, the idea emerging is that unborn children sense their mothers' stress hormone levels, programming them for greater watchfulness. We're trying to determine whether or not that sensitivity comes with greater anxiety during childhood, and if so, what we can do about it."

The team's next study will revisit these same children when they turn 6; at that point, researchers hope to give the group a battery of more definitive tests to see how the interplay between in-utero cortisol levels and sensitive parenting pans out in the long-term. Those tests would include imaging studies of the children's brains, looking to see if the higher cortisol levels may be linked to anatomical changes.

Source: University of Rochester Medical Center