It is common practice in perinatal epidemiology to calculate gestational-age-specific or birth-
weight-specific associations between an exposure and a perinatal outcome. Gestational age …

Preterm delivery is a powerful predictor of newborn morbidity and mortality. Such problems
are due to not only immaturity but also the pathologic factors (such as infection) that cause …

For many research questions in perinatal epidemiology, gestational age is a mediator that
features the causal pathway between exposure and outcome. A mediator is an intermediate …

Prospective and retrospective cohorts and case-control studies are some of the most
important study designs in epidemiology because, under certain assumptions, they can …

We thank George Davey Smith1 for his thoughtful comments on our paper2 and for drawing
attention to his previous use of a negative control exposure. We agree with his interpretation …

Abstract Purpose of Review Human reproduction is a common process and one that unfolds
over a relatively short time, but pregnancy and birth processes are challenging to study …

The 'birthweight paradox'describes the phenomenon whereby birthweight‐specific mortality
curves cross when stratified on other exposures, most notably cigarette smoking. The …

Infants of women who smoke during pregnancy have lower birthweights and have been
observed to have higher rates of perinatal mortality than infants of non-smokers. It is not …

Low birth weight (LBW) infants have lower infant mortality in groups in which LBW is most
frequent. For example, in 1991, US infants born to smokers had higher risks of both LBW …

The epidemiologic study of pregnancy and birth outcomes may be hindered by several
unique and challenging issues. Pregnancy is a time-limited period in which severe cohort …