These seats are distinguished by a carrier that can be separated from a base that's installed in the car. Because of the convenience that the carrier offers in transporting a smaller baby, they are the first choice for most new parents. We also recommend these as a first seat because they typically provide a better fit for newborns and the installation of the separate base can prove easier for parents. Many models also have features that accommodate smaller newborns or preemies with weight limits as low as 4 lbs. (See our infant car seat video.)
In the past, infant seats were commonly used until the child reached 1 year of age, typically around 22 lbs. But extensive research has shown the benefits of keeping your child rear facing for longer. And Consumer Reports, as well as the American Academy of Pediatrics, now recommend using a rear-facing seat until a child reaches age 2 or when your baby reaches the seat's height and weight limits. (See our infant car seat Ratings, available to online subscribers, for a range of tested models.)
Weight limits for some models are still at 22 pounds, but more models now offer higher weight limits, with some up to 40 lbs. depending on the model to allow rear-facing use. But when considering weight and height limits together our observations indicate that your baby is more likely to outgrow an infant seat for height well before weight. Even though most seats can accommodate babies up until they reach between 30 and 35 lbs., those same seats also have height limits of 32 inches or less. Using growth charts developed by the Centers for Disease Control for babies, an average (50th percentile) baby reaches between 30 and 35 lbs. somewhere between the ages of 2 ½ and 4, but that same baby is likely to reach a height of 32 inches sometime around the age of 18 months. A child is often also too tall for a seat when their head is less than one inch from the top of the carrier's shell. In either case, what that means is that for most people in order to keep your child in the safest rear-facing orientation until the age of 2, your next seat will need to be a convertible seat used in its rear facing mode.
Many car-seat manufacturers offer a "travel system," including an infant car seat, a base, and a stroller or frame that you snap the infant carrier into. Many stand-alone strollers can accommodate infant car seats from various manufacturers. The upside of a travel system is that they're often a good value. But it's worth noting that these systems can be bulky. If you have to negotiate subway stairs, or your trunk is small, a separate car seat and seat-carrier frame or compact stroller might be a better choice.