The Authors Reply

Excerpt

We welcome the confirmation by Yang and Waldhoer of our results [1] using data from Austria. The authors go on to make three statements, which we agree with. One is that birthweight without regard to gestational age is a strong predictor of risk. This of course is true, due to confounding by gestational age. After stratifying by gestational age, birthweight becomes a remarkably feeble predictor of risk. (We apologize if there is any confusion over our occasional shorthand use of “birthweight” for “gestational-age-stratified birthweight.”) It is worth noting that, while birthweight is correlated with gestational age, there is no birthweight criterion that effectively defines preterm delivery. Defining “prematurity” as less than 2500 g was a confusion that polluted clinical and epidemiologic research for decades [2]. …