Bedding such as thick blankets, quilts, and pillows can block an infant’s airway, leading to unintentional sleep-related suffocation. This type of bedding can also increase the risk of sudden infant death syndrome (SIDS), the unexplained death of a child within the first year of life.
Infants should be placed to sleep alone, on their backs, on a firm sleep surface, such as on a mattress in a safety-approved crib, covered by a fitted sheet. Soft objects, toys, crib bumpers, quilts, comforters, and loose bedding should be kept out of a baby’s sleep area. The baby’s bed should also be placed in the room where parents sleep.
NICHD’s Safe to Sleep campaign advises against blankets or other coverings, and recommends other actions caregivers can take to help babies sleep safely.
Source - https://www.nih.gov/news-events/nih-research-matters/unsafe-infant-bedding-use-still-common