Strange sensation in my stomach

Today I was sitting down, working on my laptop, and suddenly felt as if someone took their finger and jabbed it into the side of my stomach really hard. It didn't hurt, but startled the crap out of me! I'm only 9 weeks with didi twins so I know it's wayyyy too early to feel fetal movement, but it didn't feel like round ligament pain either. Anyone else had a weird muscle spasm like this before?