Pregnancy weight

I was looking through the threads on baby and bump, I came across a thread about weight gain week by week. On there someone had posted a link to a site that tells you how much weight you should have gained by such and such week.
Well I thought ok I know I'm under what I should be but didn't think I was that under. I am almost 28 weeks and have gained 9lbs, last time I weighed myself a few days ago. Now on this site it said I should have gained about 16lbs by now. That's more then what I gained with my son my entire pregnancy with him.

Now I know every pregnancy is different, and everyone will gain the weight differently, but do you believe in the pregnancy weight gain charts?
The ones that tell you should gain this by this.
I believe in some sense they are a good guideline, but I also think it just gives us more to worry about. If your over the max gain weight you worry you've gained to much, being under the minimum makes you worry that you've not gained enough.

I watched a baby programme today and on there on of the nurses were saying not gaining enough weight can cause the baby to have IUGR.
Now my son was born with IUGR, and I only gained 15lbs with him. Do that make it my fault he had IUGR? I know my height can be a factor, being 5ft short means baby would not have a lot of room to grow, so in that sense, it's just another factor to being my fault for the reason that my son was born with IUGR.
So if I was to look at those factors that it would make it my fault.
Other things that can cause IUGR are smoking and drinking, but I don't do either, so I know it was not because of that.
I am around smokers pretty much all the time, but I am sure that wouldn't be a factor.

With pregnancy I am finding that weight seems to be one of the biggest worry for us. whether it's because we are worried about not gaining enough or we're gaining to much.
I think the big list of foods that we can and can't eat doesn't really help.