Mittens are not a necessity for babies.
Mittens seem to be a necessity as parents want to protect their newborn from feeling cold or scratching their own face with their fingernails. Mittens are not a necessity for babies as they need to explore with their fingers - grab and feel skin - a sensory experience which helps to boost their brain structure. Also there is a risk of choking hazard when using mittens. Some hospitals now discourage mitten wearing, so don't be surprised if you notice this trend in the hospital where you deliver.
Though some baby don't really scratch themselves much, some may really grab and pull at their faces. Remember to file nails down and keep an eye on your baby but avoid mittens. Note you can file but cannot clip nails for the first couple of weeks because their finger skin is part of their nails in the beginning. Another solution to avoid scratches is to wear the long sleeved shirts that have the fold over sleeves feature to cover their hands only if needed.
If you want to put mittens on, make sure your baby is being supervised and doesn't put hands in the mouth.