Big babies

So this has nothing to do with anything that I usually post on here, but two people I knew growing up just had their first children.  (Congratulations to both Winn families!)  Both babies were late.  Now why is it that they can have an under 7 lb (6 1/2 lb) baby when they’re late, and i get a 9 lb one?  I mean, seriously.  I blame my mother and her mother, they cursed me with big baby genes.  I don’t see how my grandmother (petite tiny thing) carried a set of twins that were both 6 lbs, and my little brother was 10 lbs.  I hope I defy all general trend and as I have more children the birth weight goes DOWN.