I have been advised that if the 'tightenings' are consistent with quite severe pain that doesn't ease on rest then it's best to seek advice. I get them the most when I have been excercising or excerting myself. The pain I get is like a dull ache in my lower abdo a bit like when my period is due, but it does ease off after a couple of seconds/minutes. Hope this is of some help, but if in doubt I have found triage midwives at my local hospital fantastic for putting your mind at rest!
I've been having this the last week or so and wondered what it was. Bump goes tight like junior is pushing up right at the front and it feels all odd. Not painful, but enough to make you go 'ooh' kind of thing.
As I was typing I had one and my bump was so tight,rock hard and distorted you could almost see the shape of the baby - very weird! I also have a fibroid on the outside of my uterus that sticks out during a BH making me even more lumpy -very attractive I don't think!!!