Alessandra Ambrosio is pregnant with her first son, and she showed off her growing baby bump recently in a bikini. The supermodel turned 31 on Monday, and her picture was a way of saying thanks. She wrote to her Facebook fans, "Thank you all for the wonderful birthday wishes! Have a great weekend everybody!" We marked her milestone as well — check out Alessandra's best bikini pictures from over the years. Alessandra's off on vacation during a break from work. Alessandra also showed another recent photo from the beach to announce that she and fiancé Jamie Mazur are expecting a boy. Their new addition will make daughter Anja Mazur a big sister for the first time.