You can chose to do or not do this soon after it is born (within a week), within a few months after it is born, or only when necessary. However, it may be necessary for a birth certificate so check with your registry to cover your bases.
If CPS becomes an issue, often they just want the baby to see a pediatrician to ensure it is receiving "proper medical care." So it might be a good idea to get a newborn checkup just to have that under your belt.
Here is the story my unassisted birth with my twin girls.
Go to Birthing Methods Menu