Postpartum depression is a very common thing to happen after a woman has a baby.  It doesn't happen to everyone and there are different forms of severity of it that can happen.

Many times this happens because of the changes in the body.  After the baby is born there are hormone changes as the body goes back to how it used to be.  The thyroid at times can stop producing as much as it normally does causing depressed feelings.  A woman can be tired after having the baby which can lead to this.  Appetite and the body are completely differently for awhile.  There can also be guilt for not being as close to the baby anymore.  All these can add up into this condition.

If your wife has this, there are some things that you need to do as the husband to make sure that she is more comfortable.

First of all, recognize that this condition is real.  Many expect that after the pregnancy is over that everything will go back to how it used to be.  This is a real condition that can last a few months after the baby is born.

Be sure that you do what you can to help take care of the baby.  Your wife might need time alone or time to do other things than just take care of the baby.  Helping makes things easier.

Try not to get into arguments or fights over pointless things.  It's not the best scenario to be getting into an argument especially if it's something that is trivial.

Be careful that you don't come across as critical.  Saying things about her getting over it or whatnot can come across as cruel.  Choose your words wisely.

If the condition continues to last, she doesn't eat, or there are threats of things like suicide, get her to a doctor.  A doctor will be able to safely diagnose the problem and offer medical solutions for it.