The mood of some women is disturbed by the change in their relationship with their husbands and the start of a new relationship with the baby. The situation becomes worse if they lack intimate friends to share their secrets and troubles. The universal expectation that a new mother should be happy further contributes to guilt and depression. Hormones also play a role. High levels of female sex hormones circulate in expectant mothers' blood, but drop precipitously within hours of delivery, contributing to biochemical depression.
Pregnancy also increases levels of endorphins, the body's feel-good chemicals.
Endorphin levels fall abruptly after delivery, adding to risk of depression. A history of depression increases risk. Women with postpartum depression are more likely to have had previous mental illnesses, depression during pregnancy, and a family history of mood disorders, especially bipolar disorder. Some authorities believe that postpartum depression is more likely if a woman is in conflict with her mother and dissatisfied with the care she received as a child. According to this account, a woman who feels deprived by her own mother and rejects her as a model may find that becoming a mother herself evokes disturbing memories, makes her resent her husband and child, and heightens her sense of being ill-prepared for the new role.