H.L.
My ultrasound tech showed me three lines on the screen and was positive it was a girl... he was wrong- I had a boy!They can't be 100% certain (even if they claim it is obvious) If you really want to be certain, do the 4-D, or plan for both. Since you already have boys, look through the baby clothes and get out a few things just in case, but also get some "going home" outfits for a girl (don't cut the tags). All that being said, they are usually correct, so congrats!