You have a choice: 1) A single 20 amp circuit for all four (or more) receptacles in the four bathrooms, and the lights, fans, etc wired from a separate lighting circuit, which may include other rooms. 2) Four 20 amp circuits, one dedicated for each bathroom, including the lights, fan and maybe even a heater, too, if there is sufficient capacity. 3) A separate 20 amp circuit for each receptacle in each bathroom, with the lights and fan on any lighting circuit. 4) Two receptacles from two bathrooms on a single 20 amp circuit, 5) combinations of 3 and 4.
220.14(J) makes it clear these outlets are included in the residential general lighting load, and therefore are unlimited in the number allowed per circuit.
