(SIDS, or crib death), sudden, unexplained death during sleep of apparently healthy infant; most common cause of death for infants between 2 weeks and 1 year of age; in U.S. about 1.5 of every 1,000 babies die of SIDS; exact reason for fatal illness unknown, but research indicates increased risk for infants who sleep on their stomachs (face-down), those who are wrapped tightly in blankets, those who have colds or fevers, and those placed on soft mattresses filled with natural fibers (such as kapok) in overly warm bedrooms. see also in index Apnea