Kristin Cavallari let all of us know she's making sure she stays fit during her second pregnancy Saturday.

She showed off her modest yet growing baby bump on Instagram while working out at the gym. The former The Hills Star also added the caption, "Gym selfie....baby bump getting big!"

Cavallari glowed in black leggings, a black scoop-neck top with sleeves that went just past her elbow. Her hair was up with loose strands hanging in front of her ear. She added a pop of color with pink, white and black Nike sneakers.

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The proud mom also shared her 27th birthday celebration on Instagram earlier this month. She and husband, Chicago Bears quarterback, Jay Cutler, went out to enjoy "mock-tails", since the expecting mother can't drink alcohol. She posted a picture of her and Cutler toasting it up. She included the caption, "Thank you for all the birthday love!"

Cavallari, who is also mom to 1-year-old Camden, announced that she was four months pregnant back in November. She dished about what she is craving and confessed that her sugar fixes are the worst.

"I had a really heavy sugar phase there for a few weeks, and literally my husband had to cut me off of sugar because I broke out the worst I've ever broke out my enter life, so basically I poised myself. My body was in shock, but I had that with Camden as well."

She hasn't revealed the sex of the new baby, but said at this point she has no preference.

"I honestly don't care, I mean there's great things about both. Another boy would be fun, Cam would have a little buddy and then I'd be the woman of the house...but of course I want a little girl so I don't know. Either one would be great."