While non-medical ultrasound scans offer parents an irresistible sneak peek, the practice may not be entirely benign, according to a report published Tuesday in the British Medical Journal.

Dramatic improvements in technology, from the fuzzy Polaroids of the past to the current 3-D photographs, have shifted ultrasound from its original medical intent, the report says.

But the report notes that the U.S. Food and Drugs Administration, the American Institute of Ultrasound in Medicine and the French Academy of Medicine have all expressed reservations about ultrasound scans for non-medical purposes. The FDA suggests that casual exposure to ultrasound should be avoided, particularly during pregnancy.

Health Canada also cautions parents, saying ultrasounds should only be performed for diagnostic purposes. The federal agency also suggests fetal ultrasounds should only be performed when the expected medical benefits exceed any foreseeable risks.

"Recently, some businesses have started promoting the use of fetal ultrasound machines for the sole purpose of making videos of babies in the womb as a keepsake for parents," the federal agency says on its website. "In this setting, the ultrasound provides no information about the baby's health."

Millions of diagnostic ultrasounds performed in Canada

Diagnostic fetal ultrasounds can detect birth defects, movement, size, age and health of the infant in the womb. Health Canada says millions of diagnostic scans have been performed over the past few decades and have posed no confirmed health risk to either the mother or child.

But the federal agency cautions that there may be some evidence to suggest the scans have a biological effect on the fetus.

The BMJ report suggests that medically untrained staff may not be equipped to deal with certain crises such as if they discover a birth defect. The article acknowledges that ultrasound scans can help parents develop a sense of bonding and attachment to their child.

A study released in 2004, however, suggested that exposure to multiple ultrasound examinations in the first 18 weeks of pregnancy had no impact on growth and development.

Researcher John Newnham, of the University of Western Australia at King Edward Memorial Hospital in Perth, compared children who had been exposed to five ultrasound scans with children who had undergone one. Newnham found that there were no differences in speech, language, behaviour or neurological development between the two groups of children.