There are a few unknowns about postpartum depression, including how and why it starts, although researchers have ideas, casting suspicion on hormones, caring for the child, and the physical changes women experience. As for how long it can last, the medical literature lists a one-year period from birth. The American Academy of Pediatrics, in its screening recommendations for new mothers, end the screenings when the child is six months.

A large, recently published study now reports that a mother’s depression symptoms may last for at least three years. And not just for new mothers.

The National Institutes of Health study, led by Diane Putnick, PhD, began in 2008 and followed 5,000 women in New York State for three years after they gave birth. Researchers found that 25% of the women had high levels of depression at some point during those three years. Some of the women’s levels of depression stayed high throughout the study period. Moms who had gestational diabetes during the pregnancy or a past history of mood disorders, such as depression or bipolar disorder, were found to be at risk of having the highest levels of depression, the study showed.

The researchers assessed the women, but did not diagnose them, with a five-item screening questionnaire,

This is not the first research study to look at symptoms of depression in mothers beyond the first six months after childbirth. A study of 1,677 Finnish families demonstrated that both mothers and fathers can experience chronic depression for at least two years after the birth of their children. A 2015 study out of Brazil found that for almost 25% of the over 3,000 mothers enrolled, depressive symptoms stayed consistent from pregnancy through two years after the birth of their children.

Postpartum depression can be mistaken for the “baby blues” that some moms experience after giving birth, but baby blues do not usually last more than two weeks. Symptoms of postpartum depression can include severe mood swings, uncontrollable crying, sleep difficulties, extreme tiredness, or thoughts or feelings that make it hard to function.

The take home

If you have an infant at home and think you may be experiencing postpartum depression, call your doctor. If you have thoughts of harming yourself or your baby, seek professional help immediately. You can call 911, the National Suicide Prevention Lifeline at 1-800-273-TALK (8255), or someone close to you who can help you get the help you need.