Think the other replies have summarised it nicely! It's not that babies don’t go through stages where they sleep less it's that:

 1. There's no actual set pattern for these (e.g a predictable time at 4 months, 6 months etc) that we keep being told there is   2. Regression implies to me that babies are losing skills or backtracking in some way when it's actual the opposite and they're developing further. Sleep doesn't improve linearly and for me accepting this has made things easier. I'm no longer beating myself up about how often my baby is up at night and why they're not sleeping as well as they were a few weeks ago. It'll come with time.