Postpartum, or postnatal, depression affects a significant proportion of women after they have had a baby. It usually develops in the first four to six weeks after childbirth, although in some cases it may not develop until several months later.

Symptoms of postpartum depression include low mood, fatigue, anxiety, irritability, feeling unable to cope and difficulty sleeping, but it is often undetected and commonly under-diagnosed. It is important for postpartum depression to be recognized as soon as possible so treatment can begin.

Studies report that postpartum depression affects somewhere between one in 20 and one in four mothers. It is distinct from the so-called “baby blues,” which is a transitory state of tearfulness suffered by about half of postnatal women within about three to four days of birth. Baby blues tends to last from a few hours to several days, and there is no established link to a higher likelihood of postpartum depression.

Many people believe that postpartum depression (PPD) is caused by changes in hormone levels during and shortly after pregnancy, but this idea is disputed by some experts. Other possible triggers include inability to breastfeed (if it was hoped for), a history of depression, abuse, or mental illness, smoking or alcohol use, fears over child care, anxiety before or during pregnancy, background stress, a poor marital relationship, a lack of financial resources, the infant’s temperament or health problems such as colic, and especially lack of social support.

Genes may also play a role in predisposing women to postpartum depression. In a recent study, researchers investigated whether susceptibility can be explained by certain genetic variants. Elizabeth Corwin, PhD, of the University of Colorado-Denver, looked at three categories of genes known to code for proteins associated with depression in the general population.

But they found that “the contribution of genetic polymorphisms to the development of postpartum depression” remains unclear. “Much more research is required to understand the heritability of postpartum depression,” they write.

Clearer results have been found in studies of brain chemistry following birth. A team from the University of Toronto, Canada, explains that estrogen levels drop 100- to 1000-fold in the days following birth. Changes in estrogen levels are associated with levels of an enzyme called monoamine oxidase A (MAO-A).

The team measured MAO-A in the brain among 15 women at four to six days after birth. They saw that, “MAO-A total distribution volume was significantly elevated (by a mean of 43 percent) throughout all analyzed brain regions” compared with 15 comparison women.

They believe this mechanism could contribute to mood changes. “Our model has important implications for preventing postpartum depression and for developing therapeutic strategies that target or compensate for elevated MAO-A levels during postpartum blues,” they conclude.

Sleep, or lack thereof, has often been put forward as a possible trigger for postpartum depression. Researchers at the University of Melbourne in Australia investigated the link. They measured sleep and mood during the third trimester of pregnancy and again a week following birth, in 44 women at low risk for postpartum depression.

“After delivery, both objective and subjective night-time sleep significantly worsened with decreased total sleep time and sleep efficiency,” they report, “while daytime napping behavior significantly increased.”

Just under half (46 percent) of the women experienced a deterioration in mood, linked to subjective night-time sleep, sleep-related daytime dysfunction, and daytime napping behavior. “The perception of poor sleep, and the conscious awareness of its impact during wake-time, might share a stronger relationship with the occurrence of immediate postpartum mood disturbances than actual sleep quality and quantity,” they conclude.

Last year, experts reviewed the reliable evidence on the link between postpartum depression and diet. They write, “One biological factor given increasing consideration is inadequate nutrition. Credible links between nutrient deficiency and mood have been reported for folate, vitamin B-12, calcium, iron, selenium, zinc, and n-3 fatty acids.”

The n-3 essential fatty acids have received the most attention, they explain. “Numerous studies have found a positive association between low n-3 levels and a higher incidence of maternal depression,” they report. “In addition, nutrient inadequacies in pregnant women who consume a typical Western diet might be much more common than researchers and clinicians realize. Depletion of nutrient reserves throughout pregnancy can increase a woman’s risk for maternal depression,” they conclude.

Overall, the factors that put women at higher risk for postnatal depression are similar to those that put people at higher risk for depression at other times. Despite all of the research, PPD can start for no obvious reason, and conversely, a woman with any of these factors will not definitely have postpartum depression.

Sheila M. Marcus, MD, of the University of Michigan urges health care providers to assess risk for postpartum depression before or during pregnancy, and discuss the subject with the mother. “Routine depression screening, particularly at prenatal care visits, is paramount,” she states.

“Once a woman experiences postpartum depression, she is at risk for depression relapses with or without additional pregnancies,” she writes, adding: “Antidepressant treatments, interpersonal therapy, and behavioral treatment are often helpful strategies.”