I never heard that & I certainly hope not bc I spend so much time laughing! But it might be different for you since you have stitches..
I highly doubt that laughing hard could hurt the baby. They are so protected in there right now that a natural thing such as laughing, sneezing, coughing, vomiting.. etc is perfectley safe. I wondered the same thing about coughing like a maniac when I had a cold but everyone said I was crazy. I'm sure your doctor told you what things to avoid since you had your stitch placed and its doubtful laughter was one of them. Good Luck to you