Peripartum onset is defined as starting anytime during pregnancy or within the four weeks following delivery. There is no longer a distinction made between depressive episodes that occur during pregnancy or those that occur after delivery. Nevertheless, the majority of experts continue to diagnose postpartum depression as depression with onset anytime within the first year after delivery.The criteria required for the diagnosis of postpartum depression are the same as those required to make a diagnosis of non-childbirth related major depression or minor depression. The criteria include at least five of the following nine symptoms, within a two-week period:
Feelings of sadness, emptiness, or hopelessness, nearly every day, for most of the day or the observation of a depressed mood made by others
Loss of interest or pleasure in activities
Weight loss or decreased appetite
Changes in sleep patterns
Feelings of restlessness
Loss of energy
Feelings of worthlessness or guilt
Loss of concentration or increased indecisiveness
Recurrent thoughts of death, with or without plans of suicide

Differential diagnosis
Postpartum blues
Postpartum blues, commonly known as "baby blues," is a transient postpartum mood disorder characterized by milder depressive symptoms than postpartum depression. This type of depression can occur in up to 80% of all mothers following delivery. Symptoms typically resolve within two weeks. Symptoms lasting longer than two weeks are a sign of a more serious type of depression. Women who experience "baby blues" may have a higher risk of experiencing a more serious episode of depression later on.
Hyperglycinemia may refer to one of two related inborn amino acid disorders that are characterized by elevated levels of glycine in the blood. Propionic acidemia, also known as "ketotic glycinemia"
Glycine encephalopathy, also known as "non-ketotic hyperglycinemia"