Do you know what brackston hicks contractions are?? and l probably spelt that wrong. This is Your body is practicing for birth, l would hope you are in the care of a doctor/gyno for your pregnancy , why not give him a call on the phone , or mention this on your next visit if it is bothering you, and tell him/her your worries.
Its your own heartbeat, its your decending aorta. If not PG this would be a sign of an decending aortic anurism but because the baby is where it is this is normal. :)
I'm 26 weeks and for the past two weeks or so, I've been having the pulsating feeling as well. I have a doctor apt coming up on the 19th so I'm going to ask her about it just to be safe. I don't have any pains or anything with it, it usually goes away in a few minutes, then my little boy goes back to kicking and squirming them goes to sleep. Maybe I'm feeling it now cause I'm farther along than they think? I've noticed that everyone in this post is feeling it closer to their due date.
Your abdominal aorta is very large and pulsates. Check your pulse and see if they match. As there is more blood circulating in your body, along with increased pressure from your uterus it is likely that you are feeling your own pulse.