The reality star, 23, confirmed her happy baby news over the weekend, telling US magazine InTouch Weekly that it had been a surprise pregnancy but very much welcomed.
"We still can't believe it. It was a huge shock but we are very excited" she said.
This will be Maci's first child with partner Taylor McKinney.
Maci is also mum to son Bentley, six, whose dad is her ex-boyfriend Ryan Edwards. That pregnancy was documented in the MTV reality show 16 and Pregnant and its popular spinoff Teen Mom.
She told InTouch the pregnancy had come as a surprise to them as she was diagnosed with polycystic ovary syndrome after Bentley's birth, which can make it more difficult to become pregnant.
Maci isn't the only Teen Mom star who has announced a pregnancy this year: fellow show star Catelynn Lowell announced her pregnancy back in August.
It will be her second child with long-time boyfriend Tyler Baltierra. MTV viewers will know their first child, daughter Carly, was put up for adoption following her birth as the young couple felt it was in her best interests.
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Stars who announced pregnancies in 2014 - pictures below!
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