"Because January Jones is so slender to begin with, and didn't pack on that much weight, the show apparently had to resort to some of the makeup tricks they used on Elisabeth Moss during Peggy's pregnancy late in season 1, plus a non-pregnant body double for the bath scene," he continued.
When she got out of the tub it was an obvious double. The rest of SUndays show was a suit. They even put a pudgier schnoz on her.
Gotta say. That season opener was some of the best TV on these days.