Hot temperatures can make any of us unhappy. But they can be dangerous for pregnant women. Too much heat, and not enough fluids can actually cause an expectant mother to go into premature labor.

Dr. Terri Edersheim, of New York Hospital, explains, "Pregnancy is a time when you need a lot more fluid than you ordinarily do. You have the demands of the amniotic fluid. Pregnant women have an extra blood volume. Their kidneys are working overtime."

All of those situations also make their body temperature higher, which can be dangerous without liquids.

Doctors recommend 10 to 12 glasses of water a day for pregnant women, just to maintain their normal hydration state.