Epidemiology Seminar

Olga Basso, PhD

Associate Professor, Department of Obstetrics & Gynecology and the Department of Epidemiology, Biostatistics & Occupational Health, McGill University

Implications of using a fetuses-at-risk approach when fetuses are not at risk

Monday, 5 October 2015

4:00 pm - 5:00 pm – McIntyre Medical Building

3655 promenade Sir William Osler – Meakins – Rm 521

ALL ARE WELCOME

SYNOPSIS:

It is accepted that fetuses, not babies, are at risk of antepartum stillbirth; however, several studies examine the gestational-age- specific rates of postnatal endpoints (such as neonatal death) using fetuses as the denominator, rather than live births. Such fetuses-at-risk (FAR) approaches are appealing because many of the events relevant for infant health occur during prenatal life, and gestational time is treated as time at risk. FAR analyses also generally avoid “paradoxes” often seen when using births as the denominator, whereby exposures that are overall harmful appear protective at preterm weeks. Advocates of extending the FAR approach to encompassing postnatal outcomes claim that it provides a causal framework for perinatal epidemiology, in contrast with the “conventional” formulation based on live births at each week. Using simple examples, I will show how, when examining postnatal endpoints, using fetuses as the denominator inevitably leads to estimates that do not quite reflect the effect of length of gestation, nor that of a given exposure, on outcome. The broader issue of conditioning on specific events when studying the effect of exposures in reproductive epidemiology will also be discussed.

OBJECTIVES:

1. To illustrate the difference between the types of denominator used in perinatal epidemiology to estimate gestational-age-specific rates of a given endpoint.
2. To highlight the implications of using fetuses as the denominator for outcomes that can only be ascertained after birth
3. To discuss the broader consequences of conditioning (or not) on specific events when measuring the effect of an exposure.

BIO:

Olga Basso is Associate Professor at McGill University, with a joint appointment at the Department of Obstetrics and Gynecology and the Department of Epidemiology, Biostatistics, and Occupational Health. Her main interest is in reproductive epidemiology, with a focus on trying to disentangle the contributions of complex risk factors on child health.  Her work addresses both substantive and methodological issues.