Goo goo Gaga! Lady Gaga and her fiancé, Michael Polansky, have recently welcomed their first child together, Page Six can confirm. Additional details, including the baby’s name, sex and date of birth, are not known at this time. However, the family of three was spotted out and about for the first time in Northern California. See the exclusive first pics, obtained by Page Six, here. The musician, 40, and the entrepreneur, 42 — who have been engaged since March 2024 — have kept a low profile in recent months, leading to online speculation on their relationship status. Reps did not respond to our request for comment. Gaga (real name:…