When it comes to premature or low birth-weight babies, it's common for hospitals and parents to evaluate a newborn baby's car seat recline position to ensure that it's not compromising the child's breathing function. But full-term newborns may not be evaluated as closely.
For babies who don't have enough neck strength to hold their head upright, car seat recline angle is a delicate art that balances crash protection with comfort and breathing. If a car seat is too upright, a baby's head can flop forward, which can not only be uncomfortable, but could close off a new baby's airway—even in normal sized newborns.
Too much recline can also be dangerous, as it can allow the child's body to slide toward the top of the seat during a crash, exposing the head to injury, especially if the child is large and heavy.
Ideally, the back surface of a child car seat should be angled at around 45 degrees (about halfway back—not more) for a newborn, and can be adjusted to a slightly more upright position as the baby grows—up to about 30 degrees. Some seats, like the Baby Trend Flex-Loc car seat, for example, have started providing dual indicators. One gives recline level for babies weighing up to 20 lbs., and a second for babies weighing between 20 and 30 lbs.
In our most recent evaluations of the recline position of both infant and convertible car seat models designed to be used by newborns (see our car seats buying guide, and infant car seat Ratings and convertible car seat Ratings, available to subscribers), we took a close look at how well the recline-level indicators on each seat indicated appropriate recline position. Some seats' recline-level indicators showed the seats were correctly positioned when we determined that some were potentially too upright to keep a newborn's head sufficiently reclined. And some recline-level indicators showed that the seats were in the "correct" position over a range of reclined angles, leaving the exact (correct) position open to interpretation. Complicating matters further is the fact that if the seats of the vehicle aren't flat, they may not allow you to sufficiently recline your child's car seat without some additional bolstering under the "foot" area of the seat (a rolled towel or pool "noodle"), even after you've used the full range of the car seat's recline adjustment (if it has one).
So what's a parent to do? First, park the car on level ground when installing the car seat. Then use the car seat's manufacturer's instructions, paying close attention to the recline-level indicator on the seat, to find the correctly indicated setting for newborns. In addition, once you begin traveling with your newborn baby, we recommend you make the first few trips with him or her in the back seat, so you can observe firsthand whether the car seat is reclined enough. The baby's head should rest against the back of the car seat not only when they're asleep, but when they're awake, as well. The risk comes when the head flops forward so much that their neck isn't strong enough to lift it back up. Conversely, you don't want to recline it too far back (more than 45 degrees), which potentially increases the risk for injury in a crash.
If you're having trouble installing your seat, want someone to check your work, or think your seat may be overly upright, seek the help of a child passenger safety technician. Go to seatcheck.org or NHTSA.gov to find a child seat check event or station near you.