Outting babies to sleep on their backs may not prevent cot deaths, a specialist claims today.

The fall in cot deaths seen around the world over the last two decades may instead be the result of the natural variation witnessed in all diseases, a review of research indicates.

The number of cot deaths has halved in many countries since 1991 when campaigns were launched to persuade parents to put babies to sleep on their backs rather than prone. The measure is credited with saving the lives of thousands of babies over the intervening years and has become known as one of the simplest, most effective interventions in the history of child health.

But Dr P N Goldwater, a specialist in infectious diseases at the Women and Children's hospital in North Adelaide, Australia, casts doubt on the effectiveness of this measure.

Writing in Archives of Diseases in Childhood, Dr Goldwater says cot deaths in Sweden are rising again to the levels experienced in the early Seventies, long before the Back to Sleep campaign began.

He claims figures from Australia show a similar picture although the figures do not go back as far as they do in Sweden.

He says that if doctors and parents continue to follow the current practice of putting babies to sleep on their backs, and cot death rates continue to rise then, "reappraisal of sleep position in relation to a rising Sids [sudden infant death syndrome] will be necessary." Dr Goldwater argues that doctors are still mystified by cot death. He suggests that babies who sleep on their fronts may be more liable to take in bacteria on the surface of the sheet or mattress on which they sleep. Sleeping prone may also raise the baby's temperature, encouraging the production of potentially lethal bacterial toxins.

The theory is rejected by a leading British specialist who says putting babies to sleep on their backs has saved nearly 10,000 lives in Britain in the past decade.

Peter Blair, from the Institute of Child Health at the University of Bristol, says in a commentary in the journal that Dr Goldwater's argument is based on small sets of data which ignore the real fall in cot deaths. Although the causes of cot death are still not understood, observation has demonstrated that the research which led to the Back to Sleep campaign has been a "resounding success".