In the days after Jane Roper stopped breastfeeding her 13-month-old twin girls, her mood slumped. She took no joy in the things she normally loved, lost her motivation and found it difficult to concentrate.

Over the next few weeks, things got worse. Finally Roper, who had experienced depression before, sought help.

"It was absolutely a shock," said Roper, 37, a blogger and author of the forthcoming "Double Time."

"I had thought, and worried, about depression immediately postpartum and I was ready," she continued. "To my delight, I didn't have any kind of postpartum depression -- until I weaned my daughters."

In recent years, public health professionals, researchers and the media have bestowed greater attention upon postpartum depression, broadly defined as depression that begins within the first year or so after a woman gives birth. The Centers for Disease Control and Prevention now tracks it, and recent estimates suggest that anywhere between 9.8 and 21.3 percent of mothers in the U.S. report regular, postpartum depressive symptoms.

But the frequency with which women experience depressive episodes when weaning their babies is far less understood. Researchers have yet to examine the connection between weaning and depression in depth.

"The intersection between lactation and mood is important, and it is extremely understudied," said Dr. Samantha Meltzer-Brody, director of the perinatal psychiatry program at the UNC Center for Women's Mood Disorders. "There are definitely people who report mood symptoms associated with lactation."

In November, Meltzer-Brody worked on an overview paper on that very topic, published in the Journal of Women's Health.

Much of the piece focused on the connection between failed lactation and depression, citing estimates that only 13 percent of women in the U.S. actually achieve the six months of exclusive breastfeeding that is widely recommended. According to Meltzer-Brody, women who are forced to wean -- because of work or milk production problems, for example -- may have profoundly different psychological experiences than those who choose to stop breastfeeding when they feel ready.

And yet, both failed lactation and depression may involve the same fundamental mechanisms, which are complex and difficult to tease apart.

One major contributing factor may be actual physiological changes taking place in the body. Breastfeeding stimulates the production of hormones such as oxytocin, known colloquially as "the love hormone." Mothers' moods may plummet in its absence.

In addition, many women may experience a profound sense of grief and loss when they wean.

"We don't have the data that measure oxytocin levels with breastfeeding and weaning. It's certainly plausible that losing that is going to make people feel physically bad, independent of any cognitive sadness they're experiencing," said Dr. Alison Stuebe, an OBGYN and assistant professor of maternal and child health at the University of North Carolina and one of Meltzer Brody's co-authors.

"Research on pregnancy has been focused on the effects of pregnancy on the baby," she said. "The mom kind of disappears from the radar."

At present, some of the most powerful anecdotal reports on weaning and depression may come from the blogosphere.

Last week, Joanna Goddard, author of the popular lifestyle blog "A Cup of Jo," detailed her own struggles in a post called "The Hardest Two Months Of My Life." Rather than feeling liberated by weaning, Goddard wrote, she felt tired and sad, and quickly spiraled downward. Her mother and husband recognized the dip and encouraged her to get help, but Goddard cancelled a therapy appointment, because, she told HuffPost, she felt "too overwhelmed" to go. Weeks later, she managed a visit, but only one; she was simply too tired to continue.

"I wish I had committed to seeing a psychiatrist or psychologist, since that might have helped me feel more supported and comforted," Goddard said. "But during my depression, I didn't feel confident that they would be able to help -- I didn't think anything would help."

Susan Schade, a writer and 39-year-old mother of three, also blogged about her experience with depression and weaning. She said that it left her with what felt like the "worst PMS" she'd ever experienced. Schade was tired, nauseous, easily irritated and felt unexplained sadness. Reluctantly, she shared her feelings with a friend, who confessed she'd undergone something similar herself.

"I never sought out professional help," Schade said. "I never felt like I was a danger to myself or children. The extent of my mood swings were sadness and irritation, and they seemed to vanish as quickly as they appeared."

Indeed, the challenge for many moms may be knowing when sorrow over no longer breastfeeding their babies has tipped into more serious territory.

"Probably, a lot of what people are experiencing is a hormone change that's making them feel down, and they feel they have just lost a special relationship," said Dr. Tiffany Field, a pediatrics research professor at the University of Miami School of Medicine. "It's normal to feel sad about that. But if you're feeling changes in your activities and your sleep and they last for a few weeks, that's when you probably want to get help."

Currently, the diagnostic standard used by mental health professionals in the U.S. does not recognize depression that occurs postpartum or post-weaning as separate diagnoses.

"One way to approach the problem is to identify high-risk times in a person's life, and that would include pre- and postpartum," explained Dr. Lloyd Sederer, medical director of the New York State Office of mental health and HuffPost's mental health editor. "At these times, prevention and early intervention are critical, even if no one credible has actually proven what is happening in the brain, the hormonal system and the mind."

As long as research looking at the "what" and "why" behind depression and weaning remains relatively scant, then, the best mothers may be able to hope for is that awareness of the potential connection spreads.