I had a contraction at my 12 week scan believe it or not! And the sonographer said we have contractions all throughout pregnancy, we just dont' feel them until later on. There are triggers for contractions (like orgasm) but I am still not sure if they are called BH from early on.
I had a contraction last night and it was very painful, I wondered if BH were painful. You'd think on pregnancy 3 I'd know, but I don't! I do know my friend said she would cry with BH contractions as they hurt so much..