A proportional hazards model with time-dependent covariates and time-varying effects for analysis of fetal and infant death.
Am J Epidemiol. 2004 Aug 1;160(3):199-206.
A proportional hazards model with time-dependent covariates and time-varying
effects for analysis of fetal and infant death.
Platt RW, Joseph KS, Ananth CV, Grondines J, Abrahamowicz M, Kramer MS.
Department of Pediatrics, Faculty of Medicine, McGill University, Montreal,
Quebec, Canada.
robert.platt@mcgill.ca
Birth-weight- and gestational-age-specific perinatal mortality curves intersect
when compared by race and maternal smoking. The authors propose a new measure to
replace fetal and infant mortality and an analytic strategy to assess the effects
of risk factors on this outcome. They used 1998 data for US Blacks and Whites.
Age-specific post-last menstrual period (LMP) mortality rate was defined as the
proportion of deaths (stillbirth, perinatal death, or infant death) at a given
age post-LMP. The authors used extended Cox regression with time-varying
covariates and hazard ratios to model the effects of race and smoking on post-LMP
mortality. Perinatal mortality rates (conventional calculation) for Blacks and
Whites showed the expected crossover. However, analyses of post-LMP mortality
showed no crossover. For the Black-White comparison, a hazard ratio of 1.72
(95% confidence interval: 1.67, 1.77) was obtained. The hazard was higher for
smokers than for nonsmokers, but the hazard ratio increased from 1.09 (95%
confidence interval: 0.98, 1.22) at 22 weeks to 1.82
(95% confidence interval: 1.72, 1.92) at 40 weeks. The hazard ratio associated
with birth was also time dependent: higher than 1 for preterm gestation and
lower than 1 for term gestation. The increasing adverse effect of smoking with
gestational age suggests an accumulating effect of smoking on mortality.
Modeling post-LMP mortality eliminates the crossover paradox for race and
maternal smoking in a single statistical model.
PMID: 15257989 [PubMed - in process]
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