The first year with each of my three children was very hard. I was exhausted and sleep-deprived. Add a colicky baby, or a lack of emotional support, and you have a one-way ticket to the blues. Motherhood is most disorienting for first-time moms. Not surprisingly, they are at unusually high risk of post-partum emotional problems.
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. Finally, a history of depression increases risk. Oddly, until recently, mental health professionals have paid scant attention to post-partum depression.