I often get contacted for newborn photos after the baby has arrived and in those cases, I don't always have available appointment slots.  It breaks my heart to turn parents away.  It is best to schedule your newborn session at least one month before your due date and even better if you can do it in your 2nd trimester.  We newborn photographers schedule by due date (limiting bookings to ensure space for all of the babies when they arrive) and slots fill up.  I offer a special incentive for booking early too.  Ask me about it.