"I just love his little mouth. And that nose. Isn't that the cutest little nose? I just want to kiss him!"

Wendy Gibson is cooing over her new baby the way any mother would, except for one thing: He hasn't been born yet. Gibson, 35, is at a Brentwood, Tenn., strip mall, sitting on a bed at a chain store called Fetal Fotos, watching as an imaging specialist guides an ultrasound transducer wand over her bulging belly. She's getting her first look at her latest child, now in his 26th week of gestation. "Seeing your baby before it's born," says Gibson, the mother of three girls. "It blows my mind."

Gibson isn't the only mom-to-be anxious to behold the life growing within her. Ultrasound has been used as a diagnostic tool by doctors and their pregnant patients since at least the mid-'60s. But in recent years, imaging studios with names like A Peek in the Pod and Womb with a View have popped up in shopping centers around the country, where for fees ranging from $50 to $300 expectant parents can buy souvenir albums of ultrasound images so detailed they can make out facial features and count fingers and toes. "It was the high point of my pregnancy," says Gayla Murphy, 37, who visited Anticipation Ultrasound Studio in Tulsa 28 weeks into her first pregnancy. "I've told a lot of people to go."

Despite the enthusiasm of ultrasound studio clients, however, critics in the medical community say the technology shouldn't be taken so lightly. Experts say that even low-level exposure to the sound waves used by ultrasound can cause jarring of the fetus and raise temperatures in utero, the results of which have not been systematically studied on humans. Dr. Roy Filly, chief of diagnostic sonography at the University of California, San Francisco, Children's Hospital, cautions that while ultrasound devices are appropriate for medical use, "it's not good to use a sophisticated diagnostic instrument as a toy to entertain people."

According to Dr. Dan Schultz, acting director of the FDA's Center for Devices, ultrasound is generally regarded as safe. But some studies suggest it can influence the development of a fetus's bones and organ systems in utero, he says: "We're concerned that there's some degree of risk." Others worry about parents finding out about their child's birth defects at a strip mall rather than in the presence of trained medical staff.

Still, franchise operators insist ultrasound is safe, and there have been no reports of harm to a baby as a result. "We do it very carefully," says Dr. Leon Hansen, founder of Fetal Fotos, the nation's largest chain. According to Hansen, his studios have training programs for technicians, don't let any clients have excessive numbers of scans and require that mothers visit a doctor before the procedure. "Show me one case where the outcome of pregnancy has been harmed by what we've done," says Hansen. "Patients are grateful to have us here."

As if to prove his point, Wendy Gibson, for one, seems unable to stop marveling at the photos of her baby boy. "Nine months of pregnancy is so long," she says. "It's just incredible to see him at the halfway point."

Susan Schindehette. Eileen Finan in Brentwood