I've heard this from people, but I'm not sure it's really true. My older brother and I weighed the exact same (except I was 3 inches shorter!

)
Also, when the doctors give you an idea it really is just an estimate. I had two different doctors say that DD was close to 7 1/2 lbs. She was born 5 1/2 lbs. My doctor said that he usually doesn't say how much he thinks it is because it really is just a guess.