"Pregnant women are already undergoing a lot of physiological changes," said Dr. Eric Coris, associate professor of family medicine at the University of South Florida College of Medicine in Tampa. "Blood volume expands and sometimes blood return is not as good, so they may get swelling in certain parts of the body."
Increased blood flow and hormone changes that occur during pregnancy can make women feel hotter, and the swelling can have that same effect. As a result, women need to drink plenty of water.
Pregnant women with borderline high blood pressure also need to carefully monitor salt intake.
"Your doctor will know if it is summer swelling or something much more serious, like preeclampsia, starting to develop," said Dr. Kim Hoover, an obstetrician at the University of Alabama at Birmingham. Preeclampsia is a condition that occurs when a woman develops high blood pressure and has protein in the urine during the late second or third trimester of pregnancy. It can cause serious complications for the mother and the baby.
Besides staying indoors where it's cool, experts have advice for others who need or want to venture outside.
"People who are bedridden and don't have access to water and are not in an air-conditioned area are at highest risk of developing heat stroke," said Slovis.
Athletes who are exercising for a long period of time should drink at least 8 to 10 ounces of water every 15 minutes. If they are exercising for 30 to 60 minutes or longer, Coris says they should drink sports drinks to help replenish the salt lost through sweating.
"Salt helps the body hold on to fluid and as your sweat rate goes up, you're losing salt as well," Coris said.
But doctors also say people who are diabetic or hypertensive should be careful with sports drinks since they may contain sugar and salt.
It's also important to be aware of the signs of heat stroke, including a shallow pulse, dizziness or fainting, fever with a severe headache, loss of consciousness or signs of confusion.
"Heat stroke is the biggest danger related to heat," said Slovis.