How much does stress affect the baby?

Life has been really straddle lately. Crazy mother, dying father, husband who isn't built to handle all this, but he's trying. And trying to pass my real estate exam even bough it seems retaining any information while pregnant is futile. Does stress affect the baby in the womb? Has anyone seen this first hand? I'm trying to stay calm, but even when I breathe and smile I know inside I'm hurting.