Congratulations first off on your twins!!! About the spoitting you could be just spotting if their was intercourse involved right before you started spottinh. Some women will bleed slightly after sex for a couple days, nothing to worry about there. Another possibility is you could be one of those women who spot or bleed during their pregnancy, and no one ever knows why. Or the worst possible case would be the beginning signs of losing one of your babies, which I would say is the least possible to happen b cuz you had an us and saw heartbeats. I would not stress it unless yopur bleeding bcame more intense and accompanied cramping as well.