"Jionni and I were trying to have our second baby since November, so every month we kept taking tests," the 26-year-old Snooki & JWoww star toldUs Weekly.
Polizzi, who previously starred in Jersey Shore, already has a 19-month-old son Lorenzo with LaValle and had said she wants her kids to be close in age. The new baby, however, will not change the couple's wedding plans.
"I'm due in the fall around my wedding time. Busy year!" Polizzi added.
"I can clarify that our wedding is still on, and we are madly in love with each other. We've waited long enough and cannot wait."
Polizzi told Us she's trying to stay as fit as possible during her pregnancy.
"I also want to look somewhat in shape for my wedding. So along with still being a healthy pregnant woman, I still want to be strong and fit!" the reality TV star explained.
"[I'm] still working out with my trainer, safely, obviously, and being more conscious of the bad foods I eat. I refuse to be in labor again for 27 hours, and being active definitely helps that."
Polizzi and LaValle, 26, broke the news of their engagement and the first pregnancy in March 2012.
Fellow Snooki & JWoww star Jenni "JWoww" Farley, who is Polizzi's best friend, is also pregnant right now with her first child. Farley revealed she was pregnant in December 2013 with fiance Roger Mathews. Farley, 27, is having a baby girl.
"Jenni and I always talked about being pregnant together," Polizzi told the magazine. "I'm so excited to go through this experience with my best friend!"