not rly, it is an American study, so it should target Americans, However it is a valid concern/hypothesis that women which give birth younger tend to be of lower health overall due to various socioeconomic conditions.
Ah, but this does not claim to be a study of what age is the optimal for US women to be pregnant in given the current health care system; it supposedly makes a more general claim (or at least, that's what its title says).
