Over half of mothers experience mild mood changes after having a baby. Some women feel anxious, irritable, or sad starting around days 3-4 postpartum; this feeling is sometimes called the "baby blues" and will go away on its own. About 1-2 of every 10 women experiences postpartum depression (PPD) after delivery. These symptoms last longer than the baby blues (at least two weeks) and include low mood, sleep and appetite changes, fatigue, hopelessness, concentration problems, and anxiety, among others. Other postpartum psychiatric disorders include postpartum obsessive compulsive disorder, postpartum anxiety, and exacerbation of other underlying mental illnesses.

Postpartum psychosis (PP) is rarer and more severe than PPD and typically starts in the first few days or weeks after giving birth with mood changes including depression, mania, or a mixture of the two before progressing to psychosis. Symptoms can vary a lot and change very rapidly, even over the course of hours. Rarely, symptoms might start later than a few weeks after childbirth. PP should always be treated as a medical emergency, and most women who experience it will need to be treated in the hospital. About 1 in 1000 women will experience postpartum psychosis, and although a history of bipolar disorder is the most significant risk factor we know about, up to half of women will have no psychiatric history prior to their first episode of PP. We don't know very much about what causes PP, but we do know that a mixture of genetics, pregnancy hormones, and clinical circumstances all play a role.