In the dark days after her son was born, Kelly Modro remembers lying in bed listening to her baby cry. Unable to get up, she'd think, "Oh, my God, what did I do?"

"At first I thought it was just the hormones readjusting, but the feelings didn't go away," said the 25-year-old Monaca resident of her postpartum depression. "I even thought our dog hated me for bringing a baby home. That's how irrational I was."

While the National Institutes of Health estimates about 15 percent of new mothers like Ms. Modro suffer from postpartum depression -- defined as depressive episodes that impair maternal function -- a major new study has found the numbers to be much higher and lasting longer than previously believed.

A national survey of 900 mothers by the nonprofit organization Childbirth Connection found that about a third reported that "their postpartum physical health or emotional health interfered at least 'some' with their ability to care for their baby."

At six or more months after birth, "substantial proportions of mothers were still feeling stressed (43 percent), had problems with weight control (40 percent), experienced sleep loss (34 percent), lack of sexual desire (26 percent) and backache (24 percent)," said the study, the largest of its kind to date.

The survey, titled "Listening to Mothers II Postpartum," has sought to shed light -- and generate hard data -- on a subject that many women have resisted talking about.

While most of the 4.3 million women who gave birth in 2007 -- the largest number in years -- bounded back from the stresses of delivery, a substantial number didn't, said Maureen Corry, executive director of Childbirth Connection, which seeks to improve the quality of maternal health care.

"It's a huge physical and emotional commitment to have babies, and I don't think the world or this country responds in a way that recognizes the importance and vulnerability that women experience at this time," she said.

Most women's postpartum care officially ends at the six-week visit to the OB-GYN. For women on public assistance, government-funded health insurance also runs out at six weeks.

The Childbirth Connection study found depression and other issues persisting for months afterward, exacerbated by "the inordinate amount of responsibility for child care these mothers must take on without support from husbands, partners or others," she said.

Still, in Pittsburgh, new mothers can receive more support than elsewhere.

Any woman who gives birth at Magee-Womens Hospital can participate in a five-year, $2.5 million study funded by the National Institute of Mental Health, the only large-scale research screening program in the country.

Mothers who score more than 10 points on a postnatal depression screening scale are eligible for home visits and referrals to mental health and other support services, said Dr. Katherine Wisner, director of the Women's Behavioral HealthCARE program at Western Psychiatric Institute and Clinic and a leader of the study, which has served nearly 5,000 women since its inception two years ago.

One of them was Ms. Modro, the Monaca mother.

"They called and told me I'd scored very high on the questionnaire and that they could send someone to my house to talk with me," she said. "I figured I had nothing to lose."

Her support system was weak: Her mother died when she was 17, and her husband, a nuclear engineer, works 10-hour days, six days a week. She ended up talking with the researcher for more than two hours, and two months after giving birth, she was seeing a therapist and starting medication.

"I felt relief right away," she said. The therapist represented "another female in my life I could go talk to about whether my decisions were rational or not -- like whether I should feel guilty about putting my baby down for a nap and letting him cry it out a little, which I'd never felt I could."

"It's the best thing I've done," she added.

There's another, more controversial finding in the Childbirth Connection study -- nearly 9 percent of those surveyed experienced birth-related post-traumatic stress disorder, or PTSD, which generally affects combat veterans and crime victims.

Dr. Cheryl Beck, a professor at the University of Connecticut School of Nursing and an adviser to the study, said research has found that a difficult or violent labor -- where a mother might think she or her baby will die, along with lack of communication by health care providers -- can trigger PTSD, whose symptoms include anxiety, flashbacks and a numbness to daily life.

"Some of these women have undergone tremendous trauma while on the operating table and have experienced a real lack of caring or attention by the health care providers," said Dr. Beck.

Dr. Wisner took issue with those findings, questioning whether the women had experienced a trauma prior to childbirth or whether the PTSD was birth-related.

"Let's just say I'm skeptical," she said.

While the study's recommendations contained the usual plea for more pregnancy-related benefits for U.S. women, legislation introduced in Congress for more research on postpartum depression and mood disorders has gone nowhere, Ms. Corry said.

"And any proposals for paid maternal leave aren't going to happen in this health care environment," she added.

"Still, it's important to get this stuff out to different audiences, clinicians, policy makers, mothers and insurers.

"We need to need to recognize that postpartum recovery goes on longer than six weeks."