Dart Center for Journalism and Trauma

Postpartum mood disorders are common, but usually not extreme. Experts say about 80 percent of new mothers experience feelings of anxiety and sadness, commonly known as the baby blues, in the first two weeks after birth.

Postpartum depression is more severe and can appear anytime in the first year. Mothers may have difficulty sleeping, despite exhaustion. They may feel detached from their child and guilty because of it. They may have trouble coping, and struggle with feelings of isolation and inadequacy.

Many feel deeply ashamed.

"We are told that pregnancy and childbirth should be the happiest time of your life, but that's a cultural myth," said Diana Lynn Barnes, a clinical psychologist and specialist in postpartum mood disorders in Woodland Hills, Calif. "It's a very tumultuous time in the life of a woman, and one of the most stressful periods in her life. It's a developmental crisis and needs to be treated as such."

As a result, women tend to hide or minimize their symptoms. When they do bring them up, doctors and others sometimes make things worse by dismissing them as normal adjustment problems.

Women with histories of depression or mood disorders, and those who have had trouble with severe premenstrual syndrome symptoms — both of which Carol had — also appear to be more vulnerable to postpartum depression.

Postpartum psychosis is much rarer, and more typically happens soon after delivery, although a depression can also escalate into a full-blown delusional mindset, experts said.

Although researchers don't fully understand the brain chemistry of postpartum depression, many believe it to be biologically based and triggered in part by the massive drop in hormones that occurs after delivery.

Once the placenta is delivered, the levels of estrogen and progesterone drop precipitously. By one week out, levels of progesterone drop from 20 to 30 times their pre-pregnancy levels to next to nothing. The level of estrogen plunges to less than 1 percent of its pregnancy level.

These hormones act in part on the limbic system, the part of the brain that governs our most basic drives — appetite, sex, aggression, memory and the menstrual cycle — essentially the functions that sustain and protect life. Disrupting the regulation of these functions can prove deadly. About 5 percent of patients with postpartum psychosis kill themselves. About 4 percent kill their babies, a phenomenon that some believe drove Andrea Yates to drown her five children in June 2001.

No one knows how many patients with diagnosed postpartum depression, but not psychosis, also kill themselves.