Is Birth Weight on the Causal Pathway to Infant Mortality: Maternal Age?

Timothy B. Gage, University at Albany, State University of New York (SUNY)
Fu Fang, University at Albany, State University of New York (SUNY)
Erin O'Neill, University at Albany, State University of New York (SUNY)
Howard Stratton, University at Albany, State University of New York (SUNY)

It is a common theoretical view that (low) birth weight is a correlate of adverse birth outcomes but not on the direct, causal pathway to infant mortality. On the other hand, U.S. national policy for reducing infant mortality is to reduce low birth weight. The development of covariate density defined mixtures of logistic regression, a non-linear structural equation like model, allows a formal test of this issue. This paper determines if maternal age influences birth outcomes directly, and/or indirectly through birth weight in four populations. The results indicate that a) maternal age has direct effects on infant mortality, b) maternal age influences the birth weight distribution, but c) the effects on birth weight have no effect on mortality, that is the birth weight specific mortality curve shifts to compensate for changes in the birth weight distribution. This is consistent with the theoretical view that birth weight may not be causal.