Postpartum depression is classified as major depressive disorder with postpartum onset. It can last weeks to months. Perinatal depression includes prenatal depression, "baby blues," and postpartum depression (postpartum psychosis involves abrupt onset of psychotic symptoms; although relatively rare, it is a medical emergency).
The common feature of all of these disorders is the presence of sad, empty, or irritable mood, accompanied by somatic and cognitive changes that significantly affect the individual's capacity to function. What differs among them are issues of duration, timing, or presumed etiology.
Differentiating major depressive disorder from bipolar disorder is important, as treatment with antidepressants may adversely affect a person with undiagnosed bipolar disorder.
F32.9 – Major depressive disorder, single episode, unspecified
35489007 – Depressive disorder