Wellington, Dec 10 NZPA - Health officials have failed to push hard enough to get across the cot death safety message that babies should not share bed with adults or siblings, says an expert in the field.

"The 'softly-softly' approach has not worked," said Professor Ed Mitchell of Auckland University's paediatric department. A major concern over campaigning against bed-sharing had been that it could reduce breastfeeding, or mother-infant bonding.

"At the risk of alienating lactation consultants, Māori, and others, I believe a different, stronger and no-nonsense approach should be taken," he said today in the New Zealand Medical Journal.

Three researchers, Christine McIntosh and Alistair Gunn of Auckland University and Shirley Tonkin of the Cot Death Association, today published research in the journal arguing that some babies die in bed-sharing cases not because an adult has rolled on them, but because their jaw has been pushed backwards and their airway has been blocked by the tongue.

"This is certainly plausible and is more likely than overt `overlaying'; that is unlikely except in the rare situation that the parent is so intoxicated that they are unaware that the infant is beneath them," said Prof Mitchell.

But he noted other dangers were thermal stress and head covering, with the latter associated with a very high risk of sudden infant death syndrome (SIDS), even in infants sleeping alone.

Dr McIntosh, a senior registrar, said half the modern cot deaths in New Zealand involved co-sleeping, but her team's research showed it was not necessary to cover the face, or squash the body of a baby to restrict breathing and cause oxygen deprivation.

Because the joints at the side of the jaw were not fully formed in young babies, it could be easily displaced upwards and backwards pushing the tongue into the upper airway.

This could happen with just the infant's head rolling forward so that the chin pushed against its own chest.

Similar cases of oxygen deprivation had been seen in premature infants placed in semi-upright infant car seats, and there was evidence of full-term babies restrained in car seats with similar problems which could be related to forward slumping of the head on to the chest and pressure on the chin.

"On present evidence, all parents should be advised to sleep their baby in a cot or similar next to their parent's bed, until baby is at least six months of age," said Dr McIntosh.

Prof Mitchell said that Wellington coroner Gary Evans had recommended to the director general of health that public health advice be strengthened to make it clear that bed-sharing by adults and siblings with infants under six months exposed the infant to the risk of death.

"The issue now is how best to give this message," he said. "The current advice has been given so quietly it has not been heard.

"A recent survey found that only 46 percent identified bed sharing as a risk for SIDS, compared with 84 percent for sleep position and 73 percent for smoking."