London - Experts studying cot deaths advise parents not to share a bed with their babies in the first eight weeks of life.
It had previously been assumed that under normal circumstances sleeping with your baby was safe and even beneficial.
Only when a mother smoked or had been drinking or taking drugs was the practice thought to be dangerous.
It is now thought all bedsharing could be unsafe for very young infants in the first eight weeks of life.
Joyce Epstein, director of the Foundation for the Study of Infant Deaths (FSID), said: "The safest place for a baby to sleep is in a separate cot in the parents' bedroom."
A European study published in The Lancet medical journal looked at 745 cot-death cases, confirming a range of other risk factors.
They included babies being placed face down, having their heads covered in bedding, and sleeping under a duvet. Smoking in the home was also linked to cot death.
Six out of 10 of all cot death cases in Europe could probably be attributed to lying babies on their front or side, said the researchers.
Experts point out that the use of a sleeping bag avoids the risks associated with using a duvet and may also reduce the risk of a child overheating or sweating, and by restricting a child's movement ensures its head does not become covered.
Professor Robert Carpenter, from the London School of Hygiene and Tropical Medicine, who took part in the study, said: "It is safest if a baby sleeps in a cot, in the parents' room."
He added that smoking during pregnancy, and by either parent in the vicinity of the child once it was born, substantially increased the risk of cot death.
FSID says a baby should be placed with feet at the bottom of the cot to avoid it wriggling down and covering its head. Blankets should be tucked in firmly, and no higher than the shoulders.
The overall advice to parents is as follows:
- Cut out smoking during pregnancy. Fathers should stop smoking at this time too.
- Do not let anyone smoke in the same room as your baby.
- Place your baby on its back to sleep.
- Do not let your baby get too hot.
- Keep your baby's head uncovered - place your baby with its feet to the foot of the cot.
- Preferably sleep your baby in a cot in your bedroom for the first six months.
- Do not share a bed with your baby if you or your partner are smokers, have been drinking alcohol, take medication or drugs that make you drowsy, or feel very tired.
- Do not bed-share if your baby is less than eight weeks old.
- Do not sleep with a baby on a sofa, armchair or settee - this is considered very dangerous.
If your baby is unwell, seek medical advice promptly. - Sapa-dpa