It's tempting to over-bundle a sleeping baby during cooler months, but experts warn against it, saying it's one of the risk factors for Sudden Infant Death Syndrome, or SIDS.

"The crib should have nothing in it but the baby. So there should be no blanket, no bumper pads, nothing just the baby," says Dr. Rachel Moon from the Children's National Medical Center.

Pediatrician Rachel Moon, a Washington-based SIDS researcher, says doctors are still unsure what causes the syndrome.

"For whatever reason it seems that they stop breathing suddenly, they may not be able to arouse as well when they are sleeping because most of these babies do die while they're asleep."

For that reason, doctors encourage parents of newborns and babies up to one year of age to follow safety tips.

"Number one sleep your baby on the back, number two sleep your baby in a crib next to your bed, number three don't smoke."

Doctor Moon says there is no evidence that special mattresses or baby positioners prevent SIDS.  But she reports pacifiers, which can change the way a baby sleeps, have been effective in reducing the risk.