"It's hard to believe I will be a mom of 3 in just a few short weeks. I owe so much to my babies...they have changed me in so many ways for the better," Kristin said in the caption.
The former reality star announced in May that she and her husband, Chicago Bears quarterback, Jay Culter, were expecting another child together. The pair, who has been married since 2013, are parents to two boys: 3-year-old Camden and 17-month-old Jaxon.
In July, the couple revealed the gender of their third baby, which will mean Kristin won't be the only girl in the house anymore!
This past year, the fashion designer wrote a new book, "Balancing In Heels," which chronicles her life as a wife and mother.
"I talk about my journey to mommy-hood, my pregnancies, and how these little guys have made me who I am today in#BalancingInHeels," she said in her Instagram post. "The mommy and wife chapters are incredibly raw and real-I don't sugarcoat anything. I can't wait for u guys to read it!"
"Balancing In Heels" won't be available until 2016, but Kristin told fans they can preorder it at BalancingInHeelsBook.com.