What could this be!??

I'm 12 weeks and 3 days (second trimester) So last night I was all comfortable when all a sudden I got a strong ripping abdominal cramp that lasted for maybe 15-20 seconds and it came and went and then I felt fine. It freaked me out but does anyone know if it's just round ligament pain dues to everything stretching making room or if I should be worried? I feel refectory fine and I've had no bleeding to accompany the pain I had experienced last night so if anyone else has some insight or previous experience that would help me so much!