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.

The primary objective of this study was to evaluate the associations between psychosocial stressors, urine sugar levels, and subsequent birth outcomes, specifically high birth weight babies and Caesarean section births. In a prospective cohort study, 506 Black and White women of childbearing age were followed for the duration of one pregnancy in Tuscaloosa and Mobile counties in Alabama from 1990 to 2001. Participants were interviewed twice throughout pregnancy, during the first and third trimesters, respectively, and birth outcome data were collected via medical chart reviews. Six percent (6.1%) of the women in the sample had a high birth weight baby, and 18.4% received a C-section during childbirth. Adjusted logistic regression results indicate that urine sugar levels are predictive of high-weight births, with women who have higher urine sugar levels were more than three times likely to birth a high weight baby compared with women who have no detectable urine sugar spill (OR 3.25; 95% CI 1.30, 8.10). In addition, the interaction of familial social support throughout pregnancy, physical or verbal abuse during the second and third trimesters, and ethnicity is significantly associated with increased risk of having a high birth weight baby. For C-section, single participants are over two times less likely to receive a C-section during childbirth compared with currently married participants (OR 0.46; 95% CI 0.21-1.00). Examining structural equation modeling results; pathways leading from urine sugar levels, physical or verbal abuse during the latter half of the pregnancy, and a mother's social support among White participants are indicative of high weight births (R² = 0.65). White abused women who receive their mother's social support are more likely to have a high birth weight baby compared with both White and Black women who are not abused and receive the same amount of social support. Recommendations to public health practitioners include primary prevention through promotion of familial support during pregnancy, secondary prevention through urine sugar screening at every prenatal visit, and direct intervention by identifying and inquiring about instances of suspected abuse during pregnancy.

OBJECTIF: Chez les Autochtones, la relation entre le degré d'éloignement et les issues de naissance est inconnue. L’objectif de cette étude est d’évaluer cet impact parmi les Premières Nations du Québec. MÉTHODE : Nous avons utilisé les données vitales de Statistique Canada pour la province du Québec pour la période 1991-2000. L’ensemble des naissances géocodées parmi les communautés des Premières Nations groupées en quatre zones en se basant sur le degré d'éloignement a été analysé. Nous avons utilisé la régression logistique multi-niveaux pour obtenir des rapports de cotes ajustés pour les caractéristiques maternelles. RESULTATS : Le taux de naissances prématurées varie en fonction de l’éloignement de la zone d’habitation (8,2% dans la zone la moins éloignée et 5,2% dans la Zone la plus éloignée, P<0,01). En revanche, plus la zone est éloignée, plus le taux de mortalité infantile est élevé (6,9 pour 1000 pour la Zone 1 et 16,8 pour 1000 pour la Zone 4, P<0,01). Le taux élevé de mortalité infantile dans la zone la plus éloignée pourrait être partiellement expliqué par le fort taux de mortalité post-natale. Le taux de mort subite du nourrisson est 3 fois plus élevé dans la zone 4 par rapport à la zone 1. Cependant la mortalité prénatale ne présente pas de différences significatives en fonction de la zone malgré une fréquence élevée dans la zone 4. La morbidité périnatale était semblable en fonction de la zone après avoir ajusté pour l’âge, l’éducation, la parité et le statut civil. CONCLUSIONS : Malgré de plus faibles taux d’enfants à haut risque (accouchements prématurés), les Premières Nations vivant dans les communautés les plus éloignées ont un risque plus élevé de mortalité infantile et plus spécialement de mortalité post-néonatale par rapport aux Premières Nations vivant dans des communautés moins éloignées. Il y existe un grand besoin d’investissement en services de santé et en promotion de la santé dans les communautés les plus éloignées afin de réduire le taux de mortalité infantile et surtout post-néonatale. / OBJECTIVE: It is unknown whether Aboriginal birth outcomes may be affected by the degree of community remoteness. We assessed community remoteness and birth outcomes among Quebec First Nations. METHODS: We used Statistics Canada's vital data for the province of Quebec, 1991-2000. Postcode geo-coding linkage was used to identify all births in First Nations communities (reserves). Communities were grouped into four zones based on the degree of remoteness. Multilevel logistic regression was used to obtain the ORs adjusting for maternal characteristics. RESULTS: Preterm birth rates rose progressively from the most remote (5.2%) to the least remote (8.2%) zone (P<0.001). In contrast, infant mortality rose progressively from the least remote (6.9/1000) to the most remote (16.8/1000) zone (P<0.01). The excess infant mortality in the more remote zones could be largely explained by the high postneonatal mortality. Postnatal SIDS was 3 times higher in the most remote compared to the least remote zone. Perinatal mortality was highest in the most remote zone but the differences were not significant across the four zones. Similar patterns were observed after adjusting for maternal age, education, parity and marital status. CONCLUSIONS: Despite lower rates of preterm deliveries, First Nations living in more remote communities suffered a substantially higher risk of infant death, especially postneonatal death, compared to First Nations living in less remote communities. There is a greater need for improving maternal and infant health in more remote Aboriginal communities.

OBJECTIF: Chez les Autochtones, la relation entre le degré d'éloignement et les issues de naissance est inconnue. L’objectif de cette étude est d’évaluer cet impact parmi les Premières Nations du Québec. MÉTHODE : Nous avons utilisé les données vitales de Statistique Canada pour la province du Québec pour la période 1991-2000. L’ensemble des naissances géocodées parmi les communautés des Premières Nations groupées en quatre zones en se basant sur le degré d'éloignement a été analysé. Nous avons utilisé la régression logistique multi-niveaux pour obtenir des rapports de cotes ajustés pour les caractéristiques maternelles. RESULTATS : Le taux de naissances prématurées varie en fonction de l’éloignement de la zone d’habitation (8,2% dans la zone la moins éloignée et 5,2% dans la Zone la plus éloignée, P<0,01). En revanche, plus la zone est éloignée, plus le taux de mortalité infantile est élevé (6,9 pour 1000 pour la Zone 1 et 16,8 pour 1000 pour la Zone 4, P<0,01). Le taux élevé de mortalité infantile dans la zone la plus éloignée pourrait être partiellement expliqué par le fort taux de mortalité post-natale. Le taux de mort subite du nourrisson est 3 fois plus élevé dans la zone 4 par rapport à la zone 1. Cependant la mortalité prénatale ne présente pas de différences significatives en fonction de la zone malgré une fréquence élevée dans la zone 4. La morbidité périnatale était semblable en fonction de la zone après avoir ajusté pour l’âge, l’éducation, la parité et le statut civil. CONCLUSIONS : Malgré de plus faibles taux d’enfants à haut risque (accouchements prématurés), les Premières Nations vivant dans les communautés les plus éloignées ont un risque plus élevé de mortalité infantile et plus spécialement de mortalité post-néonatale par rapport aux Premières Nations vivant dans des communautés moins éloignées. Il y existe un grand besoin d’investissement en services de santé et en promotion de la santé dans les communautés les plus éloignées afin de réduire le taux de mortalité infantile et surtout post-néonatale. / OBJECTIVE: It is unknown whether Aboriginal birth outcomes may be affected by the degree of community remoteness. We assessed community remoteness and birth outcomes among Quebec First Nations. METHODS: We used Statistics Canada's vital data for the province of Quebec, 1991-2000. Postcode geo-coding linkage was used to identify all births in First Nations communities (reserves). Communities were grouped into four zones based on the degree of remoteness. Multilevel logistic regression was used to obtain the ORs adjusting for maternal characteristics. RESULTS: Preterm birth rates rose progressively from the most remote (5.2%) to the least remote (8.2%) zone (P<0.001). In contrast, infant mortality rose progressively from the least remote (6.9/1000) to the most remote (16.8/1000) zone (P<0.01). The excess infant mortality in the more remote zones could be largely explained by the high postneonatal mortality. Postnatal SIDS was 3 times higher in the most remote compared to the least remote zone. Perinatal mortality was highest in the most remote zone but the differences were not significant across the four zones. Similar patterns were observed after adjusting for maternal age, education, parity and marital status. CONCLUSIONS: Despite lower rates of preterm deliveries, First Nations living in more remote communities suffered a substantially higher risk of infant death, especially postneonatal death, compared to First Nations living in less remote communities. There is a greater need for improving maternal and infant health in more remote Aboriginal communities.