"Carrycots" or " infant car beds" are used for children that cannot sit in a regular baby seat, such as premature infants or infants that suffer from apnea. A carrycot is a restraint system intended to accommodate and restrain the child in a supine or prone position with the child's spine perpendicular to the median longitudinal plane of the vehicle. Carrycots are designed to distribute the restraining forces over the child's head and body, excluding its limbs, in the event of a big crash. It must be put on the rear seat of the car. Some models can be changed to face forward after the baby has reached the weight limit which is normally about 15-20 kilograms (33 to 44 lb).