Convertible car seats are designed to be versatile and adaptable to accommodate a wide range of child ages and sizes. Many convertible car seats are suitable for use from birth, and they have two modes: rear-facing mode for the first 2-4 years, and then forward-facing mode after that. Important to note that convertible car seats will not work on strollers, and are not as portable as infant car seats. They are meant to stay installed in the car, and you will have to unbuckle and move baby into a bassinet / newborn approved stroller or a baby carrier. Convertible car seats are heavy and more cumbersome to install and reinstall so they stay in the car.
When using a convertible car seat for a newborn, it's essential to ensure that the seat is properly installed and that your baby meets the minimum weight and height requirements specified by the car seat manufacturer. Additionally, it's recommended to use any included infant inserts or support cushions to provide extra comfort and support for a small baby.
However, some convertible car seats may accommodate a newborn in terms of weight and height, but they may not offer a good fit for every newborn. For example, the harness straps need to be even with or below the baby’s shoulders. If they aren't, then the car seat doesn’t fit the baby - even if the baby is the appropriate size and weight. Just something to keep in mind!