Narrator: This is Science Today. Ask any new mother what she most wants and you're likely to get the same answer: more sleep. Dr. David Claman is the director of the sleep center at the University of California, San Francisco. He says that physical and hormonal changes, as well as huge changes in the daily routine, mean that recently pregnant women sleep less than just about any other group.

Claman: In general, there are a number of studies showing that women with children, both during pregnancy and after the children are born, have a lower sleep efficiency-which means they're generally awake more often at nighttime, but there are usually additional responsibilities which disturb sleep to some degree.

Narrator: According to Dr. Claman, this sleep deprivation in new mothers may have serious psychological consequences.

Claman: In general the worst time in pregnancy is the immediate post-partum period. How much this may or may not contribute for women who end up having postpartum depression is not known but obviously we think that this is an important factor.

Narrator: For Science Today, I'm Larissa Branin.