The United Nations is growing increasingly concerned about the spread of so-called "baby boxes" for abandoned newborns, such as the one at St. Paul’s Hospital in Vancouver.

The Vancouver baby box is the only one in Canada, but the safe havens are increasingly common in Europe and UN officials say their existence is outdated and ineffective.

They are not literally boxes, but are places where a baby can be left safely and anonymously.

In some cases in Europe, men use the boxes to leave behind the babies of women forced into the sex trade.

Psychologist Kevin Browne of Britain's University of Nottingham completed a study of Europe's baby boxes, which backs a UN opinion that they violate the essential right of children to "be known and cared for" by their parents.

"There's no evidence that these baby boxes contribute to the reduction of infanticide or the reduction of abandonment," Browne said.

Browne said he was surprised to learn of the baby box at St. Paul's Hospital in downtown Vancouver, where just one child has been dropped off since its inception in 2010.

He said he worries that the anonymity of anyone who uses a box means the baby will have no medical history.

Dr. Geoffrey Cundiff, who founded the baby box at St. Paul's known as "Angel's Cradle", said the reality is that babies are abandoned all the time.

"If we can save one, to me, that is a program that is pragmatic — even if they don't know who their parents are," Cundiff said.

With files from the CBC's Jason Proctor