11/22/2011 05:15 pm ET Updated Dec 07, 2011

Consistency Of A Mother's Psychological State Vital To Child Development, New Study Shows

Developing infants can sense what their mothers are feeling, but in an unusual twist, authors of a new study suggest it isn't necessarily a woman's mental state that matters -- i.e. whether or not she's depressed -- but rather the consistency of the woman's psychological state before and after she gives birth.

The new study, slated for publication in the December issue of Psychological Science, examines how maternal depression impacts babies' mental health and motor skills. Researchers from the University of California, Irvine, followed 221 pregnant women through pregnancy and for a year following birth. They split the moms into several groups: women with no depressive symptoms, women with depressive symptoms both before and after pregnancy, and women with symptoms either before or after pregnancy -- but not both.

The researchers found that what mattered most was consistency. Development was best among babies whose moms experienced either no depressive symptoms, or who were depressed both before and after birth.

"The findings were really strong," said Curt. A Sandman, a professor in psychiatry and human behavior at UC Irvine and one of the study's authors. "Neither prenatal or postnatal depression had an impact on infant mental and psychomotor development. What mattered was whether or not there was congruence."

According to the researchers, the mechanism whereby a pregnant woman communicates her psychological state to her fetus is a mystery. It's possible that maternal stress and depression expose the fetus to elevated levels of stress hormones, they write.

But whatever the mechanism, Sandman argued that the findings suggest fetuses are somehow perceptive to their mothers' psychological state, and as they grow, gather information to prepare themselves for the environment they are likely to face. Indeed, research has suggested that depression can impact how women parent -- often in a negative way.

Dr. Ruta Nonacs, author of "A Deeper Shade of Blue: A Woman's Guide to Recognizing and Treating Depression In Her Childbearing Years," said women often follow one of two patterns: They are either less responsive to their babies, or they have greater anxiety and a tendency to hover and worry.

"During the first year of a child's life, moms play a hugely important role in helping babies develop," Nonacs said. "There's a certain synchrony between mother and child -- a child behaves a certain way, and a mom behaves in response to that. If we throw depression into that, communication between the mother and child gets to be a lot more complicated."

And this, Sandman said, is why consistency in terms of a mother's psychological state might matter.

"Even if the mothers were depressed, the fetus is collecting information to prepare for life after birth," he explained. "They're making accurate predictions about what they're going to encounter."

But the researcher cautioned that his findings do not mean that moms who are depressed before pregnancy should stay that way; rather, they should get screened for depression and get treatment early on. Estimates have suggested that nearly 15 percent of pregnant women have a new episode of depression during pregnancy, and that the same percentage have a new episode during the first three months postpartum.

In a joint report, the American College of Obstetricians and Gynecologists and the American Psychiatric Association agreed that the decision to continue or change medication for depression is one that should be made between a physician and patient, and that there is "no universal 'best answer' for all women." ACOG does not recommend universal screening, but says it should be strongly considered.

Experts caution that the new study should be considered against others that suggest a child's development is affected more by a mother's psychological state -- whether or not she is depressed -- than by the consistency of that psychological state.

"This model is very different from the prevailing approach that has found that stress during pregnancy or especially after the child is born is associated with negative developmental outcomes," said Dr. Steven Meyers, a professor of psychology at Roosevelt University and a Chicago-based clinical psychologist.

"Research to date has found that children whose mothers are depressed generally experience more problems than children whose mothers aren't depressed," he said, "regardless of whether the mother's depression matches her prenatal emotional state."