CDC study finds unsafe bedding leading cause of sudden unexpected infant deaths By Kelly Hayes Hiccups could play an important role in an infant's brain development, a new study suggests. WASHINGTON - A study from the U.S. Centers for Disease Control and Prevention found that the leading cause of sudden unexpected infant deaths (SUIDs) in the U.S. is an unsafe sleep environment — which includes soft bedding like blankets, pillows and bumper pads — despite repeated health messages about safe sleep practices. The study, published Tuesday in the journal "Pediatrics," aimed to better understand the causes of SUIDs. The term includes all unexpected infant deaths, such as those without a clear cause — referred to as "SIDS" — and those from a known cause, like suffocation.