Yolanda Favela has already seen her baby boy yawn and suck his thumb and knows he has a head full of hair — and she hasn't even met him yet.

Like many pregnant women, Favela visited an ultrasound center to view her unborn baby on a machine that captures 3-D and 4-D images. The practice allows parents to take home images, a DVD recording of the session and other souvenirs.

"It was amazing," Favela said after seeing her baby during her second visit to Stork 4D Imaging Studio in Aurora, Ill. "We made a connection with him. I know what he looks like. My husband says he looks like me."

But many in the obstetrics world aren't as excited about the trend. They have shunned so-called keepsake ultrasounds, citing a lack of regulation and scrutiny by doctors.

Ultrasound technology is generally considered safe by doctors, but it's unknown what prolonged and frequent ultrasounds could do to a fetus.

In December, the Food and Drug Administration renewed its advisory urging women not to seek ultrasounds outside their doctor's office or a hospital. In recent years several medical groups have denounced keepsake ultrasounds, including the American Congress of Obstetricians and Gynecologists, the American Medical Association and the American Institute of Ultrasound in Medicine.

Unique bonding experience

Despite the warnings, elective ultrasounds remain popular. Those who run the facilities say their ultrasounds are performed safely — mostly by technicians who used to work in medical settings — and provide a unique bonding experience. They also say clients are well-informed that a visit isn't for medical purposes.

After learning early on that they would add the first boy to their family of two daughters, the Favelas returned to Stork 4D to view clearer images. Favela said her doctor didn't express concern when she told him she planned to seek her first elective ultrasound to learn the baby's sex when she was about 15 weeks pregnant. That was more than a month before her doctor would tell her — which is another reason elective ultrasound centers are popular.

Dr. Whitney You, a maternal fetal medicine physician at Northwestern Memorial Hospital, said routine prenatal care usually doesn't involve conversations about ultrasound safety. However, if a patient brings up elective ultrasounds, she advises against them.

"The use of any medical equipment outside of its indicated use is dangerous for lots of reasons," You said. "We don't know what prolonged exposure can do to a fetus. To do something purely for entertainment reasons ... seems inappropriate."

Recreational ultrasounds could offer false reassurance to a pregnant mother, or, if something is wrong, the staff at a keepsake center wouldn't be equipped to help, You said.

The FDA agrees.

"Although there is a lack of evidence of any harm due to ultrasound imaging and heartbeat monitors, prudent use of these devices by trained health care providers is important," said Shahram Vaezy, an FDA biomedical engineer, in an agency advisory. "Ultrasound can heat tissues slightly, and in some cases, it can also produce very small bubbles (cavitation) in some tissues."

Despite the FDA warning, You has noticed an uptick in keepsake ultrasounds. She said she's not sure women are aware of the advisories, and those who are might think, "If a doctor can do them, why would it be unsafe in a mall or in a stand-alone facility where the pure focus is entertainment?"

'All about the memories'

Expectant parents use images from keepsake ultrasounds on key chains, jewelry, shower invitations and wall hangings, and also to create sculptures. Owners of the ultrasound centers also sell teddy bears stuffed with a sound box that plays the baby's heartbeat, which is recorded during the ultrasound session.

"We're all about the memories here," said Lori Dunkman, owner of the Belly Factory. Dunkman said she's a certified sonographer and opened her facility after working in a hospital. She also said she hires only people who are certified to perform ultrasounds.

Dunkman opened her business after seeing women disappointed with their hospital experience, which she said isn't as comfortable as her facility. Hospitals sometimes don't allow an expectant mother to see much on the screen. Technicians are more focused on taking measurements and other required tasks, Dunkman said.

"A lot of times [mothers] would walk away almost crying," she said. "They forget it's a medical exam. They just want to see that baby move. They want to bond with that baby."

Dunkman said she believes her ultrasounds are safe and no session is longer than 20 minutes — a precaution she has in place to prevent the ultrasound from causing any temperature changes.

The FDA warnings haven't affected business, she added. The Belly Factory, which charges $59 to $125 depending on the package, scans about 250 women a month, Dunkman said.