It was ultimately fatigue that best predicted which women would develop postpartum depression.

One of the problems with postpartum depression is that women usually aren't diagnosed until the disease is already established. If a woman's health care provider knew early on that a patient was slipping down this slope, he or she could intervene. It may not take much to screen for it, either - the questions in the fatigue test that we used took about two to three minutes to answer.

All mothers are tired right after having a baby - it helps them get the rest that they needs to recover and heal from the physical and mental stressors of childbirth. But for most women, fatigue steadily fades within the first two weeks of giving birth.