The number of expectant mothers around the country diagnosed with influenza is on the rise and obstetrician-gynecologists say there's a good reason.

Pregnant women are basically working double time as they care for the fetus, doctors say.

"The women themselves are at greater risk for catching the flu and other viral infections simply because their immune system is decreased during pregnancy. The women themselves are at greater risk to all sorts of infections that are going around," said Dr. Dan Eicher, of Rose Medical Center in Denver.

Although there's no fetal risk associated with the vaccine, a flu shot is recommended only for women who are at least 13 weeks along.

"Women who suffer an influenza infection during pregnancy, particularly in the third trimester, are at high risk for developing serious complications that can impact their health and that of the baby," said Dr. Neil Silverman, of Cedars-Sinai Medical Center in Los Angeles. "Maternal vaccination during pregnancy has been demonstrated to transfer immunity from mother to fetus, which reduces the risks for a baby born during flu season."

Silverman said vaccination rates tend to be low for pregnant women, but he hopes the early start of this year's flu season will entice more expectant mothers to seek a vaccination.

"Being 10 weeks pregnant, I'm only in my first trimester, and my doctor advised me not to get it yet," said expectant mother Jenny Riojas.

As it turned out, Riojas came down with the flu last week and she found it hard to follow her doctor's orders to the letter.

"I was really restless. I could not sleep, so you're supposed to get as much rest as possible, but I was just laying in bed not actually sleeping 'cause your body is just so sore," Riojas said.

Doctors recommend pregnant women avoid friends and relatives who have flulike symptoms. And if they do happen to get sick, the women are told to take Tylenol and drink lots of liquids.

Health experts say a fetus generally isn't affected by the flu because the virus doesn't usually cross the placenta.