US FDA warns, that pregnant women should not get videos of fetal ultrasound as souvenirs and should not use over-the-counter Doppler ultrasound heartbeat monitors, webmd.com reports.

Although both products are generally considered safe, they are approved for use only with a prescription. The increasing use of these devices for nonmedical reasons is raising concerns among health officials.

"Although there are no known risks of ultrasound imaging and heartbeat monitors, the radiation associated with them can produce effects on the body," Robert Phillips, a physicist with the FDA's Center for Devices and Radiological Health, said in an agency news release.

"When ultrasound enters the body, it heats the tissues slightly," Phillips said. "In some cases, it can also produce small pockets of gas in body fluids or tissues."

In some cases, when mothers get keepsake videos of their fetus, an ultrasound machine may be used for as long as an hour, Phillips said.

The FDA is also concerned about over-the-counter sales of Doppler ultrasound heartbeat monitors, which are used to listen to a fetus's heartbeat. The agency says these devices should be used only by or under the supervision of a health care professional.