Meghan Markle took her fetus for a night on the town Tuesday -- hitting the famous Polo Bar restaurant for dinner with her pal Serena Williams ... and we've got the video.
Her Royal Highness had a busy day -- she flew into New York for her baby shower at The Mark Hotel earlier in the day ... where friends like Abigail Spencer and Jessica Mulroney helped celebrate the mom-to-be.
Afterward, it was off to Ralph Lauren's Polo Bar -- famous for its $20 "RRL Hot Dog" -- which comes with Sauerkraut, Sweet Relish & Mustard on a Toasted Brioche.