"I thought it’d be very obvious that we would carry differently," Duncan, 27, tells PEOPLE. "I'm clearly extremely tall and hold a lot more muscle mass. Plus it was [my friend] Nat’s third pregnancy. It's my first."
Duncan, who is due with her first son on March 15th, wanted to show that every body is unique, and we shouldn't judge each other based on appearance.
Plus, women shouldn't be afraid of how their body will change when they start carrying a baby.
"It also shows women that pregnancy isn’t all about going from one extreme to another – women shouldn’t fear pregnancy," Duncan adds.
Duncan, a HIIT trainer and bodybuilder in Australia, hasn't had to change her workouts too much during her pregnancy.
"My approach to my fitness now [that I'm] pregnant has been a slow progression of modifying exercise after exercise as I get further into my pregnancy," she explains. "I've enjoyed training while pregnant and haven’t felt like it's more effort – it’s just a motherly instinct to taper particular movements as you feel the body change and ability lessen."
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"Besides having scrambled eggs instead of runny eggs, thankfully I didn’t have to change my diet," Duncan says.
She's enjoyed her pregnancy so much that she wants to add to the family – very soon!
"If all goes well, I plan to fall pregnant again this year," she says.