The reality star was given the beautiful diamond band by fiancé and long-time partner Tyler Baltierra – and couldn't wait to show it off on Instagram.
Alongside a close up image of the ring, she said: "Babe got me a new engagement ring. I wasn't expecting this at all."
Catelynn explained the ring was extra special as it has a "baby diamond on the bottom to represent our new little girl."
She added: "Thank you so much Tyler. I love you!"
Catelynn and Tyler are expecting a child together at the start of the New Year. They announced the pregnancy back in August, confirming it would be a baby girl.
This is Catelynn's second pregnancy.
Viewers of MTV reality show 16 and Pregnant and its spinoff notranslate>Teen Mum will know that she and Tyler decided to put their first daughter, Carly, up for adoption after her birth, deciding it was in the child's best interests.
They were just 16 at the time of Carly's birth.
Catelynn recently said: "We couldn't give Carly the future she deserved and so we chose adoption. We stand behind our decision. But I'm not 16 any more. We're ready for a baby."
Over the weekend, another Teen Mum star announced they were pregnant: Maci Bookout. The reality star - who is mum to son Bentley, six - is expecting a baby with boyfriend Taylor McKinney.
More celebrities who announced pregnancies in 2014:
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