Postpartum psychosis is a severe psychiatric disorder that leads to hospital admission in about one woman per 1,000 deliveries. It coincide with the vulnerable period associated with becoming a mother and may, if untreated, lead to suicide and infanticide. Some risk factors for postpartum psychosis have been identified in previous research, such as primiparity and previous psychiatric disorder.

Knowledge on how postpartum psychosis is related to obstetric factors might be helpful in the clinical risk assessment of postpartum psychosis.

The aim of this large-scale follow-up study was to examine the association between postpartum psychosis and certain pregnancy and delivery complications and other obstetric variables, after adjustment for age, year of delivery and previous hospitalization for psychiatric disorder.

1,133,368 Swedish first-time mothers were included during a 29-year period yielding 1,413 hospitalized cases of postpartum psychosis. Several obstetric variables were analyzed separately after adjustment for possible confounders.

Respiratory disorder in the neonate, severe birth asphyxia, preterm birth, caesarean section, perinatal death and SGA infant were associated with an increased risk of postpartum psychosis. After adjustment for previous hospitalization for psychiatric disorder only preterm birth and acute caesarean section remained significant risk factors for postpartum psychosis (relative risks were 1.20 and 1.31, respectively).

The relative risk of postpartum psychosis among first-time mothers with previous hospitalization for psychiatric disorder was increased more than 100-fold.

Careful clinical risk assessments of postpartum psychosis are crucial among women with a history of psychiatric disorder whereas obstetric variables have a minor importance.