The incidence of deaths related to sudden infant death syndrome (SIDS) dropped by 40 percent during the 1990s, and experts feel they're close to understanding how problems like brain abnormalities may make certain infants vulnerable in certain situations, such as sleeping facedown.

But as long as the cause of SIDS remains unknown (it still claims about 2,700 lives a year), most parents will worry as they put their baby down to sleep. Fortunately, researchers have identified ways that, while they can't guarantee full protection, will reduce a child's risk of SIDS:

1. Put your baby to sleep on her back

"This is vital," says Marian Willinger, Ph.D., special assistant for SIDS at the National Institute for Child Health and Human Development in Bethesda, Maryland. "We have evidence it definitely cuts the risk." A stomach sleeper is more likely to wiggle facedown into bedding or other items that could cover the mouth and nose and block breathing. (Sleeping on the side is safer than on the stomach, but not as good as the back.) Some parents worry that a back sleeper could choke on spit-up, but that fear appears to be unfounded: Studies have found no increase of choking episodes among babies put to sleep on their backs.

2. Place your baby on a firm mattress

Putting your baby to sleep on a plush surface, such as a waterbed, sheepskin or cushion, risks having her mouth and nose covered by the soft or pliable material.

3. Remove the soft items

Keep fluffy blankets and quilts, compressible bumper pads, stuffed animals and other soft items out of the sleep area to keep a child's head from being buried or covered.

4. Stub out

Put out the cigarettes -- preferably before pregnancy, because prenatal smoking contributes to SIDS. And don't light up later -- though exposure to secondhand smoke after birth plays a lesser role in SIDS, says Willinger, it does raise a child's risk of other illnesses, including asthma and ear infections.