Chicago - Traci Fries never dreamed that by helping to keep her baby safe from cot death she was contributing to a separate and growing medical problem.
From the nape of his neck to the top of his skull, the back of 10-month-old AJ Fries's head is perfectly flat.
The culprit, doctors told his mother, was putting AJ to sleep on his back - the increasingly common practice credited with a steep decline in crib deaths in the US.
Fries, 26, says she noticed the problem not long after AJ's birth and asked about it at every checkup. "The doctor kept saying, 'Oh, as he grows older it should fill back out.' It never did."
She has since been advised to see if her son needs to wear a special helmet to mould his head.
Skull flattening can occur because newborns' skulls are soft and malleable, which allows the growing brain to expand. The medical name is positional plagiocephaly, a condition some paediatricians had never heard of before the 1994 nationwide "Back to Sleep" campaign .
Usually harmless and easily treated, plagiocephaly has led at worst to needless tests and unnecessary operations, but some infants must wear plastic helmets, and in extreme cases surgery may be needed.
The American Academy of Paediatrics recommended periodically repositioning infants' heads while they sleep and allowing "tummy time" when they're awake. - Sapa-AP