Try this.
First, get a sitter for the child you now have.
Buy a bottle of the non alcoholic "Welches sparkling grape drink"
Preferably you, cook her a REAL nice candle light dinner with all the trimmings. The flowers "COOKIE" suggested would be best, in the form of a hand held bouqet, and dont forget to have a nice crystal vase to put them in after the tears have subsided, and place them in the middle of the table.
During the dinner, play some of her favorite songs that you have burned to a CD for her to keep afterwards.
After dinner take her to a movie she wants to see, theater, whatever.
Then As you start to leave the movie or whatever, get down on one knee, in front of her and everyone else there and tell her how you feel about her, and the child that you 2 are about to have, and how you are blessed with them all.
That should start the tears again. They love that stuff. The rest of the night is left up to you. So what do ya think?