The reality star confirmed her pregnancy by posting a picture of her blossoming baby bump to Instagram on Wednesday (6 August) evening.
Catelynn added the caption: "It's official. Four months."
Rumours that Catelynn and boyfriend Tyler Baltierra were expecting a child had been circulating for weeks.
The couple rose to fame on MTV series 16 and Pregnant, which was followed by spinoff Teen Mom. Viewers watched as Catelynn gave birth to their daughter Carly and the couple decided to give her up for adoption as they felt it was in the baby's best interests.
Catelynn, now 22, met Tyler in music class when they were both twelve. They began dating a year later then, when Catelynn was sixteen, they discovered she was pregnant.
"We couldn't give Carly the future she deserved and so we chose adoption. We stand behind our decision," said Catelynn.
"But I'm not 16 any more. We're ready for a baby,"
Catelynn and Tyler are still in contact with their adoptive daughter but have admitted the restrictions placed on their contact with her can be frustrating.
Catelynn said recently: "It's like, I gave you something you could never have and I wanted so deeply, but couldn't at that time. I'm jealous. They spend every day with her."
Last month, Tyler marked his nine-year anniversary with Catelynn by posting a sweet message to Twitter.
"It's been the best 9 years of my life with @CatelynnLowell HAPPY ANNIVERSARY BABE! Love you more than words can explain #MiddleSchoolSweet."
Congrats to Catelynn and Tyler!
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