I do the same thing as you, when participating in a conversation I don't stop to think I just blurt out whatever is on my mind, over the years I've learned to accept this as a part of me, you would not believe how many times I've embarrassed myself by doing this. I've done it some many times that embarrassment is just a part of my life now, I've got so used to it that it hardly ever bothers me anymore.

If you want to learn a little more about it, there's a link below that I have found to be useful. I've had this printed out and stuck on my desk at work to remind me. It doesn't bother me anymore but I am conscious that it may have a detrimental effect on my career so I do try to curb the impulse to speak before thinking at work and this helps.

Do You Talk to Think or Think to Talk? | Fast Company | Business + Innovation