The actress, who plays Betty in the AMC series, gave birth to a son named Xander Dane in September. She confessed that she drew on the emotions she felt during her pregnancy for the role.
"I was on such a rollercoaster of emotions - I found it really therapeutic to go to work and to be able to channel all these mood swings into Betty," Jones told People. "It was really great, actually."
Jones went on to say that viewers will see a change in Betty's wardrobe.
"We didn't do anything specifically for me because of my post-baby [body]," she added. "But Betty's had style evolution."
The actress recently insisted that her character's actions are justifiable, given how she has been treated.
The fifth season of Mad Men premieres tonight (March 25) at 9pm on AMC. It will be broadcast in the UK on Sky Atlantic on March 27.
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