Sharing a bed with a baby who is less than eight weeks old may increase the risk of cot death, research has found.
Current advice: Put your baby to sleep on its back
It had been thought it was safe to share your bed with a newborn provided you didn't smoke, drink or take drugs.
But the Foundation for the Study of Infant Deaths (FSID) has changed its advice to new parents on the back of the latest research.
Cot death experts from across Europe collaborated on The Lancet study, which focused on 745 cases.
FSID director Joyce Epstein said: "The safest place for a baby to sleep is in a separate cot in the parents' bedroom.
How to cut the risk:
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
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
If your baby is unwell, seek medical advice promptly
"Today, FSID will start alerting parents to the fact that research has found
a link between cot death and bedsharing with babies under eight weeks of age."
The researchers found a two-week-old child sharing a bed with non-smoking parents was at two-and-a-half times the risk of cot death they would be if sleeping separately.
At eight weeks they were at one-and-three-quarters the risk.
The study did not look at why sharing a bed with a small baby might increase the risk of cot death - further research is required to pin the reasons down.
It also confirmed a range of other risk factors that were already known such as babies having their heads covered in bedding, and sleeping under a duvet.
However, the researchers estimated that as many as six out of 10 of all cot death cases in Europe could probably be attributed to laying babies on their front or side, rather than their backs.
The room in which the baby sleeps should be between 16 to 20°C
At this temperature, a baby wearing a nappy, vest and babygro with one sheet will normally require two blankets as well
Blankets should be added or removed if the room is colder or hotter than recommended
Check the baby to ensure they are not too warm, as overheating can increase the risk of cot death
Professor Robert Carpenter, from the London School of Hygiene and Tropical Medicine, took part in the study.
He said: "Our analysis shows that the risk of cot death may be substantially reduced by taking a number of simple steps, most crucially ensuring the infant is put to sleep on its back, with no bedding other than a jumpsuit or Babygro, or in a well-fitting cotton or acrylic sleeping bag of not more than two or three tog.
"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.
"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.
The study, carried out by experts working for European Concerted Action on Sids, compared the home environments of cot death babies with those of 2,400 healthy infants.
Seven babies a week are thought to die from cot death in the UK.
A Department of Health spokesperson, said its advice was due to be updated, and the new research would be taken into consideration.