Pregnancy and childbirth can be a hormonal rollercoaster of the euphoric kind — except when they're not. There are many new mothers for whom the ride takes a considerably darker turn toward depression and anxiety.

New mothers experiencing postpartum anxiety or depression may feel angry and irritated with their infants. Their depression can make them feel detached, even withdrawn, and they may have trouble forming a bond with their babies.

These disturbances of mood are complicated by the fact that women are expected to enthusiastically embrace their new motherhood, and this makes it hard for women to feel they can discuss the feelings they're having openly.

The amygdala is usually hyperactive in anxious and depressed people, but for the women with PPD, the amygdala can actually be less activated.

The mood and emotional disorders that arise during pregnancy or shortly after giving birth have largely been ignored by clinicians and researchers. Even though postpartum depression (PPD) and postpartum anxiety affect nearly 1 in 10 women, they are still treated as extensions of major depression and generalized anxiety disorder, respectively.

Recently, postpartum depression (PPD) has been recognized as a distinct diagnosis in the DSM, the text that sets the criteria for diagnosing mental conditions. “Perinatal depression,” is listed as a subset of major depression in the DSM. Postpartum anxiety, estimated to be just as prevalent as PPD, has yet to be recognized in the DSM.

Now, a new study has found that postpartum depression and postpartum anxiety produce different effects in the brain from other forms of depression and anxiety.

“If you think that 10%-20% of women during pregnancy and the postpartum period will suffer from depression and/or anxiety, and then you realize there are only 20 publications looking at the neurobiology of these illnesses, it's quite shocking,” Jodi Pawluski, one of the authors of the new study, said in a statement.

“Motherhood really can change the mother, which is something we often overlook,” said Pawluski. “It is not always a happy time, and we need to understand that, talk about it, and figure why it can trigger mental illnesses in so many women. If we can improve the health and well-being of the mother, we will improve the health and well-being of the child and family.”

When the team compared fMRI scans of neural activity in women with PPD to those of people with major depression who had not given birth, they saw distinct patterns for new mothers with PPD. For example, the amygdala is usually hyperactive in anxious and depressed people, but for the women with PPD, the amygdala can actually be less activated.

Postpartum mood disorders do not only affect mothers. Their infants are also affected. Children of depressed mothers have higher medical claims than do children of healthy women. They have more medical office and emergency department visits than do children of non-depressed mothers. The authors estimate the annual cost of not treating a mother with depression, in lost income and productivity alone, to be $7,200.

The study is published in Trends in Neurosciences.