Many parents, and even some doctors, mistakenly believe that infants can ride facing forward as soon as their neck muscles are strong enough to hold their heads up. The problem isn't muscle strength but elastic vertebrae and ligaments which can permit an infant's spinal column to stretch as much as two inches. The spinal cord, however, can only stretch about inch before rupturing. Keeping the baby rear-facing until age one keeps the head from being propelled forward in a crash, preventing devastating spinal cord injuries. Most rear-facing child restraints can accommodate infants weighing up to 20 or 22 pounds.
Many models come with a removable base, which can be left in the vehicle once it is installed.
Rear-facing child safety seats extend forward in the vehicle, close to the airbag module, thus creating the potential for serious or fatal injuries from contact with a deploying airbag. For vehicles with passenger-side airbags and no back seat, the safest way to transport your infant is another vehicle. Most convertible seats are rated up to 30 or even 35 pounds rear-facing, a must for infants who exceed 20 pounds prior to their first birthdays. Because of their size, it may be difficult to fit some convertible seats in the rear seats of very small vehicles. As with all child safety seats, try it in your vehicle before you buy it.