The Jersey Shore star welcomed baby Lorenzo in August, just months after wrapping filming on her spin-off reality series Snooki & JWoww.
Polizzi tweeted a picture of herself and her son to fans on Friday (November 23), adding: "My favourite birthday gift... Best birthday ever with my fiancé @JLaValle and Lorenzo!!"
Snooki, who rose to fame with her hard partying on MTV, has since calmed down in the wake of her son's birth.
She recently revealed that she "already wants more kids" with partner Jionni LaValle in the near future.
With Snooki settling down and other breakout star The Situation sober, MTV recently confirmed that Jersey Shore will finish for good after the current sixth season ends.