title: Parametric modelling of neonatal mortality in relation to size at birth.
abstract: We use a richly parameterized model to analyse the effects of shortness and thinness at birth on neonatal mortality in Swedish live-born singletons. The model captures the hazard of neonatal mortality according to the function alpha x exp(-gamma x t) + delta, where t represents age. Covariates are allowed to simultaneously influence the initial excess hazard, the rate of decay, and the long-term hazard. Among term newborns, birth length for gestational age had a stronger effect on the long-term hazard and a weaker effect on the initial excess hazard than the Ponderal index. The initial excess hazard associated with a low Ponderal index tended to decay quickly. Among preterm newborns, a higher birth length for gestational age was associated with lower initial and long-term hazards, and with a faster rate of decay of the initial excess hazard. In contrast, the Ponderal index was not associated with the long-term hazard. We discuss the interpretability of the model and its potential use in neonatology and medical demography. We also compare the model to a Cox model with time-dependent covariates.
authors.affiliation: Clinical Trials Centre, Faculty of Medicine, University of Hong Kong, Hong Kong SAR, PR China. cheungyb@graduate.hku.hk
authors.forename: Y B
authors.initials: YB
authors.lastname: Cheung
authors.forename: P S
authors.initials: PS
authors.lastname: Yip
authors.forename: J P
authors.initials: JP
authors.lastname: Karlberg
mesh_terms: D000704:Analysis of Variance; D001719:Birth Certificates; D001724:Birth Weight; D001824:Body Constitution; D001827:Body Height; D015992:Body Mass Index; D005314:Embryonic and Fetal Development; D005260:Female; D005865:Gestational Age; D006801:Humans; D007226:Infant Mortality; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D016013:Likelihood Functions; D008297:Male; D015233:Models, Statistical; D016016:Proportional Hazards Models; D012042:Registries; D012307:Risk Factors; D012727:Sex Characteristics; D017678:Sex Distribution; D016019:Survival Analysis; D013548:Sweden / Q000453:epidemiology; D013997:Time Factors