The 27-year-old broke the news to Us Weekly, saying that she and fiancé Roger Mathews were "super excited and super emotional" to discover the gender of their first child.
Among those sending well-wishes to Jenni via Twitter was her best friend and co-star Nicole 'Snooki' Polizzi, who said: "YAY finally I can go shopping with @JENNIWOWW for BABY GIRL THINGS!"
Snooki added that her son Lorenzo, one, is "so excited" about the impending arrival.
Coincidentally, Jwoww's pregnancy announcement has come while Snooki is promoting her new book Baby Bumps, which documents her pregnancy and experience of motherhood.
Snooki and fiancé Jionni LaValle welcomed their first child, Lorenzo, in August 2012.
Chatting to Reveal last May, Jwoww said: "Nicole is an amazing mum, but her life has changed – for the better. I'd like to be selfish for a little while longer before I decide to have babies though. We both want children, but one thing I love about Roger is that there is no pressure. Of course I'd love two or three kids in the next five years, but there's no rush."
Jenni revealed her pregnancy to fans on Christmas Day, saying that she and Roger couldn't have asked for a better Christmas gift.
"We wanted to share this exciting news with you all first because you have been a part of our lives these past few years and seen the love between Roger and me develop and blossom," she wrote. "We are so excited to share this new chapter of our lives with you as we become parents and create more memories with a new addition to our family!"
Jenni and Roger became engaged in September 2012 in a rather unique way: Roger popped the question while the couple were skydiving!
More celebrity babies coming! Star pregnancies announced in 2014:
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