The health economics of macrosomia
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
High birth weight (also known as macrosomia) is a problem that has as of yet received little attention by health researchers, in particular, health economists. High birth weight is a concern mostly due to the increased difficulties it presents during birth for both the mother and the baby but there is also concern that high birth weight may continue to present negative effects later in the baby’s life. Many factors have been attributed as risk factors for high birth weight including mother’s age, ethnicity, parity, obesity, weight gain during pregnancy, infant gender, and gestation length. However, there is a dearth of careful analysis dedicated to determining the extent of causality of these risk factors where endogeneity concerns are present. In this thesis, I examine various issues surrounding high birth weight. I describe the situation in New Zealand (Chapter 2) to see if our experience with high birth weight reflects that found in international research. I analyse the relationship between socio-economic status and high birth weight (Chapter 3) to explore whether high socio-economic status has a unique effect on high birth weight compared to other health disorders in which it generally helps alleviate the incidence. I further investigate the relationship between obesity and high birth weight (Chapter 4) in an attempt to disentangle the causal effect of obesity on high birth weight risk from the mere correlation that has been well documented. I explore the possibility of vitamin and mineral supplements taken during pregnancy being a risk factor for high birth weight (Chapter 5), then address the potential endogeneity issues to identify a causal impact. Finally, I return to the definition of high birth weight (Chapter 6) and consider the optimal way to define the “problematic” weight threshold and whether this threshold should depend on gestation length or the ethnicity of the mother. My findings suggest that in New Zealand, the incidence of macrosomia varies by the ethnicity and weight group of the mother and the gender of the infant. Socio-economic status does seem to affect high birth weight risk but the nature of the relationship is complex. Obesity only appears to have a significant causal effect on high birth weight risk for women who are morbidly obese, but even for these women conventional estimation that disregards the endogeneity of obesity greatly exaggerates the effect. There does appear to be a correlation between iron supplementation and high birth weight risk but the relationship does not withstand controlling for endogeneity. My findings indicate that the currently accepted threshold used to define macrosomia is justified as it does consistently predict adverse health outcomes. However, flexible definitions which consider different grades of macrosomia or different thresholds for different ethnicities could improve on the current definition.