Well, it doesn't mean much. It means when they run a measuring tape over the outside of your tummy, they get a measurement that is larger than the average measurement for 30 weeks, by a little bit. But averages, of course, include people who are over the mark and people who are under the mark. And measuring from the outside isn't the best way to assess what is on the inside.
By the way this doesn't indicate one way or another that your baby is bigger than average. I actually measured average to smaller than average with all 3 of my babies and they all came out (naturally mind you) at over 9lbs each! In fact with my first, they did an u/s at 37 weeks because they thought I looked too small for dates and that I might have IUGR (intra uterine growth retardation) - she came out 3 weeks later at 9lbs 1oz. So don't believe everything they measure - and also some drs measure differently each time they measure even! They are measure roughly from your pubic bone to the top of your uterus and you should measure 30cm for 30weeks and 31cm for 31 weeks etc so if it's off by a cm or 1/4 of an inch then it's not a problem...I wouldn't give it a second thought. Unless it was a drastic loss or gain then it would be worth considering. Sounds to me like you're right on track for your dates! Good luck!
i am measuring 34 cm at 30weeks pregnant. is there any major concern
I'm pretty sure if you are measuring 34cm that means you are measuring 34 weeks. It isn't a big concern since there is some room for error in measuring this way. It could mean that your baby is a little bigger or it could mean that you have some extra fluid, both reasons really aren't a cause for concern.
Anytime you have a question or concern you should ask your dr, that's what they are there for, they will be able to explain it better than anyone else!
My sister measured 4 weeks ahead with her last pregnancy and I measured 2 weeks ahead with my last, we both ended up with 9 1/2 pound babies, so it can vary a lot from women to women.