Generally it's true. I read it's because after your uterus has already stretched it stretches easier or there's more room so they can grow bigger. Dunno if that's true though lol.
But with me it was true, first baby was 5lb 15oz and second was 6lb 11oz, bith were born at the same gestation (according to scan dates anyway).
That's kind of why I hope this one comes early or on time... I don't mind going overdue at all I just don't want a giant baby haha. I'm used to having tiny newborns who stay looking 'newborn' for longer so it'll be a shock if I end up with a 9 or 10lb-er lol.
That said, I've seen a few 'new' babies recently (at the local shop, and my neighbour's) and they look tiny and when I ask what they weighed (at birth) it's been about 7lb something, and they were 3/4/5 weeks old and still looked tiny even though by then they must have weighed 9/10lb at least.
Today I saw my aunt's foster baby, and he looked tiny and felt so light, but he must be around the 10-11lb mark, possibly a bit more (he's not been weighed since he was 5 weeks old and only weighed 6lb 15 then lol, he's 11 weeks now so guessing he weighs at least 10lb now).