Wow, it's kind of like reading slashdot - you go to the linked article and it says something *totally different* than the summary! Anyway, women pregnant with boys don't gain more weight - the article indicates that they consume extra calories, which, rather than causing additional weight gain, end up accounting for the larger size of newborn boys.
This is not a surprising finding. It would have been a metabolic mystery if women were able to produce larger male newborns without consuming additional calories.