"My BIRTHDAY GIFT this year is EXTRA SPECIAL," Bayleigh, 29, wrote to her followers.
"Being a mom is all I've wanted for as long as I can remember. I used to dream of being a wife and a mother & now I am living those dreams."
Bayleigh also shared pictures from a maternity shoot she had with her 27-year-old husband.
In one image, Bayleigh stands topless while Chris kisses her growing baby bump, and they're both rocking nothing but blue jeans.
Bayleigh waited quite some time to announce her pregnancy given she's already eight months along.
"I can't believe I'm going to be a mommy in a few weeks," Bayleigh added in her post.
Chris also gushed about the pregnancy on his own Instagram account, sharing photos of his wife.
"To have a baby coming in GENERAL... is a blessing. But to have a baby with my favorite person in the universe? It makes it even better," Chris wrote.
Chris also mentioned Bayleigh's birthday, writing, "To Bay, I'm so blessed to have a kid with you. I love how open we are, how much we communicate, and everything we've been through... HAPPY BIRTHDAY TO YOU."
Chris promised in his post to give his unborn child "the world."
"Everything I do is for YOU!" he added. "You will have the best life ever, I swear. THE BEST LIFE EVER!!!! We'll see you in a few weeks. Cheers to our baby. I love you forever!"
It's widely reported Bayleigh and Swaggy got married in a quiet, secret ceremony with family in February 2019 after meeting and falling in love on Big Brother's 20th season.
Although Swaggy was evicted from the Big Brother house early on, he and Bayleigh bonded over their shared trauma, when they went through a miscarriage together.
Bayleigh experienced the miscarriage while living in the jury house, and Swaggy was apparently very supportive during the difficult and emotional time.
The couple got engaged during the show's finale in September 2018, and three months after the proposal, Chris and the former Miss Missouri USA purchased their first home together and moved into a raised ranch-style house.
"My first pregnancy didn't happen the way that I had dreamt it. It was an unplanned and sudden surprise," Dayton continued in her Wednesday post.
"But, as soon as I found out I was pregnant that baby was the only thing that mattered to me at all. When I lost it, I was devastated. I never really recovered from the loss. I just didn't feel like I could do anything right."