The combination of an expected condition with a such a severe disease shocked me, so I had to look it up.

http://en.wikipedia.org/wiki/Postnatal_depression  

Postnatal depression (also called postpartum depression and referred throughout this article by the acronym PPD) is a form of clinical depression which can affect women, and less frequently men, after childbirth. Studies report prevalence rates among women from 5% to 25%, but methodological differences among the studies make the actual prevalence rate unclear.[1]

Rates of PPD decreased as income increased...

Postnatal psychosis or PNP, is a mental illness, which involves a complete break with reality.

Only 1 to 2 women per 1,000 births (.1% to .2% of births) develop postnatal psychosis.

Our knowledge has surpassed our wisdom. -Charu Saxena.