Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Epidemiology and Biostatistics

Supervisor

Dr. M. Karen Campbell

Abstract

Research suggests increased risk for adverse outcomes associated with late preterm (34-36 weeks) and early term (37-38 weeks) birth versus full term (39-41 weeks). However, it remains unclear to what extent these outcomes are associated with physiological immaturity or factors leading to or associated with early birth.

The first objective was to elucidate the role of gestational age in determining risk of poor neonatal outcomes in the context of biological determinants of preterm birth. A retrospective cohort study of singletons delivered at 34-41 weeks to London-Middlesex (Canada) mothers was conducted using perinatal and discharge abstract databases (N=38,807, 2002-2011). Modified Poisson regression showed increased risk for NICU triage/admission and respiratory morbidity among infants born late preterm and early term. The effect of gestational age was partially explained by biological determinants (infection and inflammation, placental ischemia and other hypoxia, other [diabetes/hydramnios]) acting through gestational age. Placental ischemia and other hypoxia exacerbated the effect of gestational age on poor outcomes.

The second objective was to elucidate the role of gestational age in determining risk of poor developmental outcomes in the context of proximal social processes. A secondary analysis of singletons delivered at 34-41 weeks was conducted using the National Longitudinal Survey of Children and Youth (N=15,099, 2-3 years; N=12,203, 4-5 years). Modified Poisson regression did not show increased risk for developmental delay or receptive vocabulary delay among children born late preterm or early term. Proximal social processes (parenting interactions, effectiveness, consistency) did not modify the effect of gestational age but were strong predictors of poor outcomes.

The third objective, secondary to central analyses, was to examine associations between biological determinants of preterm birth and gestational age among spontaneous singleton births (perinatal database; N=17,678). Multinomial logistic regression showed associations between these pathological processes and both late preterm and early term birth.

Poor neonatal outcomes among infants born late preterm and early term are due to physiological immaturity and also to biological determinants of preterm birth acting through and with gestational age to produce poor outcomes. Beyond the neonatal period, social factors are the most important influences on development in births close to full term.


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