- Email: [email protected]
Longitudinal Rates and Risk Factors for Adverse Birth Weight Among First Nations Pregnancies in Alberta
OBSTETRICS
Longitudinal Rates and Risk Factors for Adverse Birth Weight Among First Nations Pregnancies in Alberta Richard Thomas Oster, PhD, Ellen Louise Toth, MD Department of Medicine, University of Alberta, Edmonton, Alberta
Abstract Objective: We wished to identify the prevalence, longitudinal trends, and associated risk factors for various birth weight categories by First Nations ethnicity in the province of Alberta. Methods: We performed a retrospective analysis of administrative data for the years 2000 to 2009 inclusive. Age-adjusted prevalence trends for high birth weight (HBW; > 4000g), very HBW (> 4500g), low birth weight (LBW; < 2500g), and very LBW (< 1500g) were compared via average annual percent change analyses. Logistic regression analysis was used to determine risk factors. Results: First Nations ethnicity was a significant independent predictor of HBW (OR 1.82 [95% CI 1.75, 1.89]), very HBW (OR 2.35 [95% CI 2.18, 2.52]), and very LBW (OR 1.35 [95% CI 1.23, 1.48]), but not of LBW (OR 0.98 [95% CI 0.93, 1.03]). However, HBW prevalence decreased and other birth weight categories remained stable over time in First Nations populations. Gestational diabetes and maternal weight 91 kg were potentially manageable risk factors for HBW. Potentially manageable risk factors for LBW included pregestational renal disease, hypertension, and maternal weight 45 kg, as well as smoking, illicit drug dependence, and alcohol consumption. Conclusion: Although HBW, very HBW, and very LBW remain more common in Alberta First Nations populations than in the general population, their prevalence is not increasing.
Résumé Objectif : Nous souhaitions identifier la prévalence, les tendances longitudinales et les facteurs de risque connexes pour ce qui est de diverses catégories de poids de naissance chez les populations des Premières Nations dans la province de l’Alberta. Méthodes : Nous avons mené une analyse rétrospective des données administratives pour les années 2000 à 2009, inclusivement. Les tendances, corrigées en fonction de l’âge, de la prévalence pour ce qui est du poids de naissance élevé (PNÉ; > 4000 g), du poids de
Keywords: Birth weight; Indigenous population; Aboriginal population; Epidemiology; Longitudinal; Retrospective study; North America Received on June 4, 2015 Accepted on July 25, 2015 http://dx.doi.org/10.1016/j.jogc.2015.10.011
naissance très élevé (PNTÉ; > 4500 g), du poids de naissance faible (PNF; < 2500 g) et du poids de naissance très faible (PNTF; < 1500 g) ont été comparées par l’intermédiaire d’analyses de la modification annuelle moyenne en pourcentage. Une analyse de régression logistique a été utilisée pour déterminer les facteurs de risque. Résultats : L’ethnicité « Premières Nations » a été un facteur prédictif indépendant significatif de PNÉ (RC, 1,82; IC à 95 %, 1,75, 1,89]), de PNTÉ (RC, 2,35; IC à 95 %, 2,18, 2,52) et de PNTF (RC, 1,35; IC à 95 %, 1,23, 1,48), mais non de PNF (RC, 0,98; IC à 95 %, 0,93, 1,03). Cependant, la prévalence du PNÉ a connu une baisse et les autres catégories de poids de naissance sont demeurées stables avec le temps au sein des populations des Premières Nations. Le diabète gestationnel et le poids maternel 91 kg ont été des facteurs de risque potentiellement gérables en ce qui concerne le PNÉ. Parmi les facteurs de risque potentiellement gérables en ce qui concerne le PNF, on trouvait la maladie rénale prégestationnelle, l’hypertension, le poids maternel 45 kg, le tabagisme, la dépendance aux drogues illicites et la consommation d’alcool. Conclusion : Bien que le PNÉ, le PNTÉ et le PNTF demeurent plus courants au sein des populations albertaines des Premières Nations que dans la population générale, leur prévalence n’est pas en hausse. Copyright ª 2016 The Society of Obstetricians and Gynaecologists of Canada/La Société des obstétriciens et gynécologues du Canada. Published by Elsevier Inc. All rights reserved.
J Obstet Gynaecol Can 2016;38(1):29e34
INTRODUCTION
W
e have shown recently in a large longitudinal administrative dataset that high-risk pregnancies and poor outcomes are more common among First Nations women than in the general population in the province of Alberta.1 First Nations are Canada’s most populous Aboriginal group, and similar poor outcomes have been found for Indigenous women in international settings.2 In our previous analysis (which was focused on diabetes in pregnancy epidemiology) we noted a disproportionately JANUARY JOGC JANVIER 2016
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higher risk of both low birth weight (LBW) and high birth weight (HBW) among infants born to First Nations women.1 Birth weight is a key determinant of morbidity and mortality in both infancy and early childhood, and can also affect health outcomes in adult life.3,4 However, there is little information about the epidemiology of birth weight in First Nations populations because longitudinal changes have not been rigorously explored, and data on risk factors are limited. The purpose of this study was to gain a better understanding of the epidemiology (prevalence, longitudinal changes, and associated risk factors) of various birth weight categories in the province of Alberta, particularly among First Nations. Our overall aim was to provide knowledge that could lead to better pregnancy care/interventions and lowered risk of adverse birth weight outcomes. METHODS
We conducted a secondary analysis of anonymized administrative records, and therefore informed consent was not required. Data for the years 2000-2009 had been previously acquired from the Alberta Perinatal Health Program (APHP). In Alberta, the APHP collects and stores perinatal data from the provincial delivery record for all hospital births and registered midwife-attended home births. Delivery record information obtained from prenatal records and/or from the patient is recorded by a health care provider (usually a nurse) on the delivery record when a pregnant woman presents for delivery. For each variable included in the analysis, data were complete or nearly complete (available for 97% to 100% of pregnancies). In addition to birth weight, maternal risk factors explored included age, parity, ethnicity, pre-existing hypertension, gestational diabetes (GDM), pre-existing diabetes, diabetes retinopathy, proteinuria, chronic renal disease, pregestational weight (defined as either 45kg or 91kg), anemia, multiple gestation, illicit drug dependence, smoking use (at any time during pregnancy), alcohol use (at any time during pregnancy), history of abortion, history of preterm infant, history of neonatal death, history of stillbirth, history of Caesarean section, history of fetal anomaly, history of small for gestational age (SGA) neonate, and history of large for gestational age (LGA) neonate. A detailed description of all of the included variables is provided in our previous publication, as are statistical comparisons of these variables between First Nations and non-First Nations populations.1 In the years 2000-2009 there were 433 445 pregnancies in Alberta. Only records with gestational age 20 weeks were included in the analysis. Records with missing birth weight data were not
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included. A total of 426,945 pregnancy records were analyzed. Three distinctive populations of Canadian Indigenous people are recognized in Canada: First Nations, Métis (mixed blood), and Inuit. In Alberta, there are approximately 116,670 First Nations people and 96,865 Métis people, representing approximately 3.3% and 2.7% of the provincial population, respectively.5 Only approximately 1600 Inuit people live in Alberta. First Nations and Inuit individuals whose Nations have engaged in Treaties are granted “registered Indian” or Treaty status, under the federal Indian Act of Canada. The Alberta Health Care Insurance Plan Central Stakeholder Registry file includes an identifier for such individuals. Thus, to determine First Nations ethnicity, the data were sent to Alberta Health and matched via the Personal Health Number. Women delivering in Alberta with a First Nations identifier (First Nations or Inuit) were considered “First Nations”, whereas all other women (including First Nations individuals without Treaty status and Métis individuals) were considered “nonFirst Nations”. All statistical analyses were performed using STATA version 11 (StataCorp LP, College Station, TX) and Joinpoint version 3.5.1 (Informer Technologies Inc., Rockville, MD) statistical software. We categorized infants based on their birth weight as either normal birth weight (2500g4000g), HBW (> 4000g), very HBW (> 4500g), LBW (< 2500g), and very LBW (< 1500g). Annual age-adjusted prevalence values and 95% confidence intervals (CIs) of the four birth weight categories were compared (using csquare analysis) by ethnicity. For the prevalence calculations, the denominator was the total number of pregnancies for which data on that variable were available for the specific group of interest. The numerator was the total number of pregnancies for which the criteria for the variable of interest were met, for the specific group of interest. Average annual percent change (AAPC) values and 95% CIs in birth weight prevalence over time were calculated. The AAPC provides a summary measure of the trend over a pre-specified fixed interval. An AAPC with a P value of < 0.05 was considered to be a statistically significant change over time. Statistical modelling using multivariable purposeful logistic regression was used to evaluate the relationships between the various birth weight categories and possible explanatory variables.6 Briefly, independent variables with a P-value < 0.20 in the univariate linear regression analysis were fitted in a multivariable model. Variables with a P-value > 0.05 were removed, and the potential confounding effect of each variable was assessed. Odds
Longitudinal Rates and Risk Factors for Adverse Birth Weight Among First Nations Pregnancies in Alberta
Figure 1. Age-adjusted prevalence of adverse birth weight categories over time in Alberta by ethnicity
HBW prevalence First Nations
Very HBW prevalence First Nations
Non-First Nations
25
15
Rate, %
Rate, %
20
10 5 0
5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
Year
Year
LBW prevalence First Nations
Very LBW prevalence First Nations
Non-First Nations
Non-First Nations
3.5
12
3
10
2.5
8
Rate, %
Rate, %
Non-First Nations
6 4
2 1.5 1
2
0.5
0
0 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
Year
Year
ratios (ORs) and 95% CIs were calculated. The linear assumptions of continuous variables and potential interaction effects were assessed.
1.23, 1.48]). First Nations ethnicity was not a significant predictor for LBW in the full adjusted model (OR 0.98 [95% CI 0.93, 1.03]).
Ethics approval for the study was provided by the Human Research Ethics Board of the University of Alberta.
For non-First Nations infants, significant decreases in prevalence over time were observed for both HBW and very HBW; however, LBW prevalence increased significantly over time (Figure 1, Table 1). HBW prevalence also decreased significantly but other birth weight categories remained stable over time among First Nations infants (Figure 1, Table 1).
RESULTS
Compared to non-First Nations, infants born to First Nations women had significantly higher (P < 0.01) overall age-adjusted prevalence values for HBW (11.0% [95% CI 10.89, 11.07] vs. 17.7% [95% CI 17.59, 17.82]), very HBW (1.6% [95% CI 1.60, 1.67] vs. 4.2% [95% CI 4.15, 4.27]), LBW (7.1% [95% CI 7.07, 7.22] vs. 8.8% [95% CI 8.73, 8.90]), and very LBW (1.6 [95% CI 1.55, 1.62] vs. 2.6% [95% CI 2.56, 2.66]). After adjustment for other mediating variables in multivariable logistic regression, First Nations ethnicity remained a significant independent predictor of HBW (OR 1.82 [95% CI 1.75, 1.89]), very HBW (OR 2.35 [95% CI 2.18, 2.52]), and very LBW (OR 1.35 [95% CI
For First Nations women, the final adjusted multivariate models for each birth weight category are shown in Table 2. GDM and pre-gestational maternal weight 91 kg were potentially manageable risk factors for HBW among First Nations women. There was a significant interaction effect between pre-gestational weight 91kg and GDM for very HBW. The OR for very HBW in women with both GDM and pre-gestational weight 91kg was 5.07 (95% CI 3.73, 6.89) compared to women
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Table 1. Average annual percent change (AAPC) in the age-adjusted prevalence of birth weight categories among pregnancies in Alberta, 2000-2009 (n [ 426 945). Values are AAPCs (95% CI) First Nations (n ¼ 28 286)
Non-First Nations (n ¼ 398 659)
High birth weight
2.1 (3.3, 0.8)
2.4 (2.8, 2.1)
Very high birth weight
0.3 (2.3, 1.8)
3.6 (5.0, 2.1)
Low birth weight
0.7 (1.6, 3.0)
1.1 (0.6, 1.6)
Very low birth weight
0.2 (3.0, 3.6)
0.7 (0.7, 2.1)
without GDM and without weight 91kg. Thus, there is an additive effect of pre-gestational weight 91kg and GDM on very HBW. Smoking, illicit drug dependence, and alcohol consumption were negatively associated with HBW. Potentially manageable risk factors for LBW included pregestational renal disease, hypertension, and maternal weight 45 kg, as well as smoking, illicit drug dependence, and alcohol consumption. Pre-gestational maternal weight 91 kg was negatively associated with LBW.
DISCUSSION
Our study confirms an increased prevalence and risk of HBW in First Nations populations compared to nonAboriginal populations.2,7e9 We report the same 82% increased risk of HBW after adjustment for other predictors as was shown by systematic review and metaanalysis for Canadian Aboriginal populations compared to non-Aboriginal populations.2 Much of the epidemiology of HBW in First Nations has been examined among the James Bay Cree populations of northern Quebec, with rates of 34.3%,7 36.5%,10 37.2%,11 and 36.1%12 being reported. Little is known about the prevalence of HBW in western provinces. Our observed rate of HBW in First Nations in Alberta (17.7%) is considerably lower, and similar to that reported in First Nations in Manitoba (20.1%).8 That the prevalence of GDM is notably lower among Alberta (6.1%)1 and Manitoba (6.9%)8 First Nations compared to the prevalence among the James Bay Cree (18.6%)11 may partly explain the lower risk of HBW. GDM has been shown to be a strong risk factor for HBW in First Nations populations,7,8,10 as has maternal
Table 2. Significant adjusted multivariate predictors of birth weight categories among First Nations women in Alberta (n [ 28 286). Values are odds ratios (95% CI) Age 17*
HBW (n ¼ 4903)
Very HBW (n ¼ 1075)
-
-
LBW (n ¼ 2206) 0.76 (0.62, 0.94)
Very LBW (n ¼ 640) -
Age 35*
-
-
1.61 (1.39, 1.87)
1.48 (1.16, 1.90)
Parity (0)†
-
-
1.07 (1.02, 1.13)
-
Male sex
1.45 (1.36, 1.54)
1.62 (1.42, 1.84)
-
-
Multiple gestation
-
-
16.31 (14.00, 19.00)
8.93 (7.18, 11.12)
Chronic renal disease
-
-
3.18 (1.23, 8.18)
7.80 (2.72, 22.40)
Pre-existing hypertension
-
-
3.44 (2.39, 4.94)
2.45 (1.35, 4.44)
Gestational diabetes mellitus
1.70 (1.49, 1.94)
2.18 (1.77, 2.68)§
Pre-gestational weight 45kg
-
-
1.82 (1.010-2.99)
-
Pre-gestational weight 91kg
2.32 (2.14, 2.53)
2.76 (2.40, 3.18)§
0.54 (0.46, 0.64)
0.52 (0.39, 0.71)
Drug dependant
0.56 (0.47, 0.67)
0.63 (0.44, 0.89)
2.05 (1.76, 2.39)
1.64 (1.24, 2.16)
Smoker
0.66 (0.62, 0.71)
0.62 (0.54, 0.70)
1.29 (1.17, 1.43)
-
Alcohol
0.88 (0.78, 0.99)
-
1.45 (1.26, 1.67)
1.34 (1.05, 1.72)
History of abortion
-
-
1.40 (1.20, 1.63)
2.03 (1.61, 2.55)
History of neonatal death
0.65 (0.44, 0.95)
-
1.55 (1.11, 2.17)
2.35 (1.47, 3.78)
History of stillbirth
0.72 (0.56, 0.93)
-
2.18 (1.73, 2.74)
3.05 (2.18, 4.27)
History of preterm
0.77 (0.71, 0.83)
0.72 (0.61, 0.84)
1.76 (1.59, 1.94)
1.30 (1.09, 1.55)
History of LGA
4.48 (3.74, 5.38)
5.88 (4.69, 7.36)
0.29 (0.16, 0.52)
-
History of SGA
0.41 (0.23, 0.75)
-
3.64 (2.60, 5.09)
-
History of Caesarean section
0.82 (0.74, 0.91)
-
1.24 (1.09, 1.42)
-
LGA: large for gestational age; SGA: small for gestational age. *Compared to age 18-34. †
Compared to parity ¼ 1 or 2.
§
Significant interaction effect between pregestational weight 91kg and gestational diabetes.
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-
-
Longitudinal Rates and Risk Factors for Adverse Birth Weight Among First Nations Pregnancies in Alberta
obesity.10,11,13 Our large dataset and access to numerous potential confounders allowed for robust multivariable logistic regression analyses, showing for the first time a significant additive effect of both maternal GDM and maternal obesity on very HBW risk in First Nations infants. Such women were five times more likely to have a very HBW infant. We were encouraged by the significant decrease in HBW and stability of very HBW longitudinally among infants born to First Nations women in Alberta. To our knowledge, the only other examination of trends in a Canadian Aboriginal population has been in a recent study of Quebec First Nations. In this group, a slight upward trend was observed for HBW rates; the rates were approximately 18.2% in 1981-1989 and 19.8% in 2000-2008.9 In the same study, inequalities in very HBW between First Nations and non-First Nations expanded as rates increased for First Nations from approximately 5.4% to 7.5%.9 In Alberta, the prevalence of GDM has not increased for First Nations women between the years 2000 and 2009,1 perhaps explaining to some degree the lack of increase in HBW and very HBW. Our finding that First Nations ethnicity is not a predictor of LBW after adjusting for confounders supports data from the same recent systematic review and meta-analysis, which found no increased risk of LBW for Canadian Aboriginal populations compared to the non-Aboriginal population.2 We also show that in contrast to the nonFirst Nations population, LBW is not increasing in Alberta First Nations, which supports data from northern Quebec First Nations where no increase was seen over a 10 year period.14 However, rates appear to be higher in Alberta (8.8%) than in British Columbia Bella Coola First Nations (5%)15 and northern Quebec Cree First Nations (2.4%).10 Our study is the first to examine very LBW in a First Nation population, and the first to examine longitudinal trends in very LBW in an Indigenous group. We found First Nations infants were significantly more likely to have very LBW compared to non-First Nations, yet rates have not increased over time. In contrast, data from the early 2000s in the United States showed no difference in the prevalence of very LBW among American Indians (1.3%) and their Caucasian counterparts (1.2%).16 For the general population of Alberta we report significant decreases in HBW and very HBW longitudinally. This supports data from large national studies, including National Center for Health Statistics data in the United States suggesting that overall birth weights have decreased (by 52g) between 1990 and 2005 in the United States17 and Canadian Vital Statistics data indicating a decrease in HBW
prevalence (from 16.8% to 14.4% among infant males and 10.6% to 8.8% among infant females between 2000 and 2007).18 This decrease in HBW despite continued increases in rates of obesity and diabetes,19,20 and falling smoking rates,21 cannot be explained by our study and requires further investigation. It has been suggested that declines in gestational age at birth may partly explain the declines in HBW.17 However, trends are not consistent across nonAboriginal populations in Canada, because the prevalence of HBW actually increased significantly from 16.2% to 17.5% between 1992 and 2005 in Newfoundland and Labrador22 and from 7.1% to 9.2% between 1981-1989 and 2000-2008 in Quebec.9 Canada has the lowest national rate of LBW of the G7 nations,23 but rates remain higher than those in Scandinavian nations.18 In the 2012 general Canadian population, LBW occurred in approximately 6.2% births nationally; rates have remained relatively stable over the past three decades based on Vital Statistics data.23 However, geographical differences are apparent, as we report a slightly higher prevalence of LBW among the general Alberta population (7.1%), with rates increasing over time. Similarly, Simonet et al.14 found the rate of LBW increased between 1991 and 2000 from 5.5% to 7.6% in nonAboriginal communities in northern Quebec. The observed ethnic (First Nations vs. non-First Nations) disparities may be underestimated. Our findings cannot be generalized to non-registered First Nations individuals and Métis individuals, as these individuals could not be identified and were included in the non-First Nations population group. The contributions of access to health care, lifestyle, gestational weight gain, social environment, socioeconomic status, and other potential contextual predictors to the logistic regression models could not be assessed. We hypothesize that ethnic disparities in these factors likely contributed to the increased risk of various birth weight categories in the First Nations infants. CONCLUSION
Our study is the first to rigorously explore the age-adjusted prevalence of birth weight categories longitudinally in a First Nations population. Although HBW, very HBW, and very LBW remain more common in Alberta First Nations than in non-First Nations, it is encouraging that their prevalence is not increasing. Earlier and better management of both maternal obesity and GDM in First Nations women could lead to less HBW infants. Strategies to decrease LBW risk should aim to reduce smoking, illicit drug dependence, and alcohol consumption among pregnant First Nations women, and to improve pre-gestational
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renal disease and the identification and management of hypertension. ACKNOWLEDGEMENTS
This study was funded in part by the Canadian Institutes for Health Research, Institute of Aboriginal Peoples Health. This study is based on data provided by the APHP and Alberta Health. The interpretation and conclusions contained herein are those of the researchers and do not necessarily represent those of the Alberta Perinatal Health Program, Alberta Health, or the Government of Alberta. Neither the Alberta Perinatal Health Program, nor Alberta Health, nor the Government of Alberta expresses any opinion in relation to this study. REFERENCES 1. Oster RT, King M, Morrish DW, Mayan MJ, Toth EL. Diabetes in pregnancy among First Nations women in Alberta, Canada: a retrospective analysis. BMC Pregnancy Childbirth 2014;14:136.
9. Auger N, Park AL, Zoungrana H, Fon Sing M, Lo E, Luo ZC. Widening inequality in extreme macrosomia between Indigneous and non-Indigenous populations of Quebec, Canada. Aust N Z J Public Health 2013;37(1):58e62. 10. Willows ND, Sanou D, Bell RC. Assessment of Canadian Cree infants’ birth size using the WHO Child Growth Standards. Am J Hum Biol 2011;23(1):126e31. 11. Brennand EA, Dannenbaum D, Willows ND. Pregnancy outcomes of First Nations women in relation to pregravid weight and pregnancy weight gain. J Obstet Gynaecol Can 2005;27(10):936e44. 12. Armstrong IE, Robinson EJ, Gray-Donald K. Prevalence of low and high birthweight among the James Bay Cree of northern Quebec. Can J Public Health 1998;89(6):419e20. 13. Oliveira AP, Kalra S, Wahi G, McDonald S, Desai D, Wilson J, et al. Maternal and newborn health profile in a First Nations community in Canada. J Obstet Gynaecol Can 2013;35(10):905e13. 14. Simonet F, Wilkins R, Luo ZC. Temporal trends in Inuit, First Nations and non-Aboriginal birth outcomes in rural and northern Quebec. Int J Circumpolar Health 2012;71. 15. Thommasen HV, Klein MC, Mackenzie T, Grzybowski S. Perinatal outcomes at Bella Coola general hospital: 1940 to 2001. Can J Rural Med 2005;10(1):22e8. 16. Mathews TJ, Menacker F, MacDorman MF. Centers for Disease Control and Prevention, National Center for Health Statistics. Infant mortality statistics from the 2002 period: linked birth/infant death data set. Natl Vital Stat Rep 2004;53(10):1e29.
2. Shah PR, Zao J, Al-Wassia H, Shah V. Knowledge Synthesis Group on Determinants of Preterm/LBW Births. Pregnancy and neonatal outcomes of Aboriginal women: a systematic review and meta-analysis. Womens Health Issues 2011;21(1):28e39.
17. Donahue SM, Kleinman KP, Gillman MW, Oken E. Trends in birth weight and gestational length among singleton term births in the United States: 1990-2005. Obstet Gynecol 2010;115(2 Pt 1):357e64.
3. Barker DJ, Winter PD, Osmond C, Margetts B, Simmonds SJ. Weight in infancy and death from ischaemic heart disease. Lancet 1989;2(8663):577e80.
18. Health Canada. The Well-being of Canada’s Young Children. Available at: www.dpe-agje-ecd-elcc.ca/eng/ecd/well-being/sp_1027_04_12_eng.pdf; 2011. Accessed March 8, 2015.
4. Oster RT, Luyckx VA, Toth EL. Birth weight predicts both proteinuria and overweight/obesity in a rural population of Aboriginal and non-Aboriginal Canadians. J Dev Orig Health Dis 2013;4(2):139e45.
19. Twells LK, Gregory DM, Reddigan J, Midodzi WK. Current and predicted prevalence of obesity in Canada: a trend analysis. CMAJ Open 2014;2(1):E18e26.
5. Statistics Canada. National Households Survey, 2011. Aboriginal Peoples in Canada: First Nations people, Métis, and Inuit. Available at: http://www12. statcan.gc.ca/nhs-enm/2011/as-sa/99-011-x/99-011-x2011001-eng.pdf; 2011. Accessed February 26, 2015.
20. Oster RT, Johnson JA, Hemmelgarn B, King M, Balko SU, Svenson L, et al. Recent epidemiologic trends of diabetes mellitus among status Aboriginal adults. CMAJ 2011;183(12):E803e8.
6. Bursac Z, Gauss CH, Williams DK, Hosmer DW. Purposeful selection of variables in logistic regression. Source Code Biol Med 2008;3:17.
21. Reid JL, Hammond D, Burkhalter R, Rynard VL, Ahmed R. Tobacco Use in Canada: Patterns and Trends. Waterloo, ON: Propel Centre for Population Health Impact, University of Waterloo; 2013 Edition.
7. Rodrigues S, Robinson EJ, Kramer MS, Gray-Donald K. High rates of infant macrosomia: A comparison of a Canadian native and a non-native population. J Nutr 2000;130:806e12.
22. Edwards NM, Audas RP. Trends of abnormal birthweight among full-term infants in Newfoundland and Labrador. Can J Public Health 2010;101(2):138e42.
8. Aljohani N, Rempel BM, Ludwig S, Morris M, McQuillen K, Cheang M, et al. Gestational diabetes in Manitoba during a twenty-year period. Clin Invest Med 2008;31(3):E131e7.
23. Employment and Social Development Canada. Indicators of Well-being in Canada. Available at: http://well-being.esdc.gc.ca/misme-iowb/.3ndic.1t.4 [email protected]?iid¼4; 2011. Accessed March 31, 2015.
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Longitudinal Rates and Risk Factors for Adverse Birth Weight Among First Nations Pregnancies in Alberta Richard Thomas Oster, PhD, Ellen Louise Toth, MD Department of Medicine, University of Alberta, Edmonton, Alberta
Abstract Objective: We wished to identify the prevalence, longitudinal trends, and associated risk factors for various birth weight categories by First Nations ethnicity in the province of Alberta. Methods: We performed a retrospective analysis of administrative data for the years 2000 to 2009 inclusive. Age-adjusted prevalence trends for high birth weight (HBW; > 4000g), very HBW (> 4500g), low birth weight (LBW; < 2500g), and very LBW (< 1500g) were compared via average annual percent change analyses. Logistic regression analysis was used to determine risk factors. Results: First Nations ethnicity was a significant independent predictor of HBW (OR 1.82 [95% CI 1.75, 1.89]), very HBW (OR 2.35 [95% CI 2.18, 2.52]), and very LBW (OR 1.35 [95% CI 1.23, 1.48]), but not of LBW (OR 0.98 [95% CI 0.93, 1.03]). However, HBW prevalence decreased and other birth weight categories remained stable over time in First Nations populations. Gestational diabetes and maternal weight 91 kg were potentially manageable risk factors for HBW. Potentially manageable risk factors for LBW included pregestational renal disease, hypertension, and maternal weight 45 kg, as well as smoking, illicit drug dependence, and alcohol consumption. Conclusion: Although HBW, very HBW, and very LBW remain more common in Alberta First Nations populations than in the general population, their prevalence is not increasing.
Résumé Objectif : Nous souhaitions identifier la prévalence, les tendances longitudinales et les facteurs de risque connexes pour ce qui est de diverses catégories de poids de naissance chez les populations des Premières Nations dans la province de l’Alberta. Méthodes : Nous avons mené une analyse rétrospective des données administratives pour les années 2000 à 2009, inclusivement. Les tendances, corrigées en fonction de l’âge, de la prévalence pour ce qui est du poids de naissance élevé (PNÉ; > 4000 g), du poids de
Keywords: Birth weight; Indigenous population; Aboriginal population; Epidemiology; Longitudinal; Retrospective study; North America Received on June 4, 2015 Accepted on July 25, 2015 http://dx.doi.org/10.1016/j.jogc.2015.10.011
naissance très élevé (PNTÉ; > 4500 g), du poids de naissance faible (PNF; < 2500 g) et du poids de naissance très faible (PNTF; < 1500 g) ont été comparées par l’intermédiaire d’analyses de la modification annuelle moyenne en pourcentage. Une analyse de régression logistique a été utilisée pour déterminer les facteurs de risque. Résultats : L’ethnicité « Premières Nations » a été un facteur prédictif indépendant significatif de PNÉ (RC, 1,82; IC à 95 %, 1,75, 1,89]), de PNTÉ (RC, 2,35; IC à 95 %, 2,18, 2,52) et de PNTF (RC, 1,35; IC à 95 %, 1,23, 1,48), mais non de PNF (RC, 0,98; IC à 95 %, 0,93, 1,03). Cependant, la prévalence du PNÉ a connu une baisse et les autres catégories de poids de naissance sont demeurées stables avec le temps au sein des populations des Premières Nations. Le diabète gestationnel et le poids maternel 91 kg ont été des facteurs de risque potentiellement gérables en ce qui concerne le PNÉ. Parmi les facteurs de risque potentiellement gérables en ce qui concerne le PNF, on trouvait la maladie rénale prégestationnelle, l’hypertension, le poids maternel 45 kg, le tabagisme, la dépendance aux drogues illicites et la consommation d’alcool. Conclusion : Bien que le PNÉ, le PNTÉ et le PNTF demeurent plus courants au sein des populations albertaines des Premières Nations que dans la population générale, leur prévalence n’est pas en hausse. Copyright ª 2016 The Society of Obstetricians and Gynaecologists of Canada/La Société des obstétriciens et gynécologues du Canada. Published by Elsevier Inc. All rights reserved.
J Obstet Gynaecol Can 2016;38(1):29e34
INTRODUCTION
W
e have shown recently in a large longitudinal administrative dataset that high-risk pregnancies and poor outcomes are more common among First Nations women than in the general population in the province of Alberta.1 First Nations are Canada’s most populous Aboriginal group, and similar poor outcomes have been found for Indigenous women in international settings.2 In our previous analysis (which was focused on diabetes in pregnancy epidemiology) we noted a disproportionately JANUARY JOGC JANVIER 2016
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higher risk of both low birth weight (LBW) and high birth weight (HBW) among infants born to First Nations women.1 Birth weight is a key determinant of morbidity and mortality in both infancy and early childhood, and can also affect health outcomes in adult life.3,4 However, there is little information about the epidemiology of birth weight in First Nations populations because longitudinal changes have not been rigorously explored, and data on risk factors are limited. The purpose of this study was to gain a better understanding of the epidemiology (prevalence, longitudinal changes, and associated risk factors) of various birth weight categories in the province of Alberta, particularly among First Nations. Our overall aim was to provide knowledge that could lead to better pregnancy care/interventions and lowered risk of adverse birth weight outcomes. METHODS
We conducted a secondary analysis of anonymized administrative records, and therefore informed consent was not required. Data for the years 2000-2009 had been previously acquired from the Alberta Perinatal Health Program (APHP). In Alberta, the APHP collects and stores perinatal data from the provincial delivery record for all hospital births and registered midwife-attended home births. Delivery record information obtained from prenatal records and/or from the patient is recorded by a health care provider (usually a nurse) on the delivery record when a pregnant woman presents for delivery. For each variable included in the analysis, data were complete or nearly complete (available for 97% to 100% of pregnancies). In addition to birth weight, maternal risk factors explored included age, parity, ethnicity, pre-existing hypertension, gestational diabetes (GDM), pre-existing diabetes, diabetes retinopathy, proteinuria, chronic renal disease, pregestational weight (defined as either 45kg or 91kg), anemia, multiple gestation, illicit drug dependence, smoking use (at any time during pregnancy), alcohol use (at any time during pregnancy), history of abortion, history of preterm infant, history of neonatal death, history of stillbirth, history of Caesarean section, history of fetal anomaly, history of small for gestational age (SGA) neonate, and history of large for gestational age (LGA) neonate. A detailed description of all of the included variables is provided in our previous publication, as are statistical comparisons of these variables between First Nations and non-First Nations populations.1 In the years 2000-2009 there were 433 445 pregnancies in Alberta. Only records with gestational age 20 weeks were included in the analysis. Records with missing birth weight data were not
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included. A total of 426,945 pregnancy records were analyzed. Three distinctive populations of Canadian Indigenous people are recognized in Canada: First Nations, Métis (mixed blood), and Inuit. In Alberta, there are approximately 116,670 First Nations people and 96,865 Métis people, representing approximately 3.3% and 2.7% of the provincial population, respectively.5 Only approximately 1600 Inuit people live in Alberta. First Nations and Inuit individuals whose Nations have engaged in Treaties are granted “registered Indian” or Treaty status, under the federal Indian Act of Canada. The Alberta Health Care Insurance Plan Central Stakeholder Registry file includes an identifier for such individuals. Thus, to determine First Nations ethnicity, the data were sent to Alberta Health and matched via the Personal Health Number. Women delivering in Alberta with a First Nations identifier (First Nations or Inuit) were considered “First Nations”, whereas all other women (including First Nations individuals without Treaty status and Métis individuals) were considered “nonFirst Nations”. All statistical analyses were performed using STATA version 11 (StataCorp LP, College Station, TX) and Joinpoint version 3.5.1 (Informer Technologies Inc., Rockville, MD) statistical software. We categorized infants based on their birth weight as either normal birth weight (2500g4000g), HBW (> 4000g), very HBW (> 4500g), LBW (< 2500g), and very LBW (< 1500g). Annual age-adjusted prevalence values and 95% confidence intervals (CIs) of the four birth weight categories were compared (using csquare analysis) by ethnicity. For the prevalence calculations, the denominator was the total number of pregnancies for which data on that variable were available for the specific group of interest. The numerator was the total number of pregnancies for which the criteria for the variable of interest were met, for the specific group of interest. Average annual percent change (AAPC) values and 95% CIs in birth weight prevalence over time were calculated. The AAPC provides a summary measure of the trend over a pre-specified fixed interval. An AAPC with a P value of < 0.05 was considered to be a statistically significant change over time. Statistical modelling using multivariable purposeful logistic regression was used to evaluate the relationships between the various birth weight categories and possible explanatory variables.6 Briefly, independent variables with a P-value < 0.20 in the univariate linear regression analysis were fitted in a multivariable model. Variables with a P-value > 0.05 were removed, and the potential confounding effect of each variable was assessed. Odds
Longitudinal Rates and Risk Factors for Adverse Birth Weight Among First Nations Pregnancies in Alberta
Figure 1. Age-adjusted prevalence of adverse birth weight categories over time in Alberta by ethnicity
HBW prevalence First Nations
Very HBW prevalence First Nations
Non-First Nations
25
15
Rate, %
Rate, %
20
10 5 0
5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
Year
Year
LBW prevalence First Nations
Very LBW prevalence First Nations
Non-First Nations
Non-First Nations
3.5
12
3
10
2.5
8
Rate, %
Rate, %
Non-First Nations
6 4
2 1.5 1
2
0.5
0
0 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
Year
Year
ratios (ORs) and 95% CIs were calculated. The linear assumptions of continuous variables and potential interaction effects were assessed.
1.23, 1.48]). First Nations ethnicity was not a significant predictor for LBW in the full adjusted model (OR 0.98 [95% CI 0.93, 1.03]).
Ethics approval for the study was provided by the Human Research Ethics Board of the University of Alberta.
For non-First Nations infants, significant decreases in prevalence over time were observed for both HBW and very HBW; however, LBW prevalence increased significantly over time (Figure 1, Table 1). HBW prevalence also decreased significantly but other birth weight categories remained stable over time among First Nations infants (Figure 1, Table 1).
RESULTS
Compared to non-First Nations, infants born to First Nations women had significantly higher (P < 0.01) overall age-adjusted prevalence values for HBW (11.0% [95% CI 10.89, 11.07] vs. 17.7% [95% CI 17.59, 17.82]), very HBW (1.6% [95% CI 1.60, 1.67] vs. 4.2% [95% CI 4.15, 4.27]), LBW (7.1% [95% CI 7.07, 7.22] vs. 8.8% [95% CI 8.73, 8.90]), and very LBW (1.6 [95% CI 1.55, 1.62] vs. 2.6% [95% CI 2.56, 2.66]). After adjustment for other mediating variables in multivariable logistic regression, First Nations ethnicity remained a significant independent predictor of HBW (OR 1.82 [95% CI 1.75, 1.89]), very HBW (OR 2.35 [95% CI 2.18, 2.52]), and very LBW (OR 1.35 [95% CI
For First Nations women, the final adjusted multivariate models for each birth weight category are shown in Table 2. GDM and pre-gestational maternal weight 91 kg were potentially manageable risk factors for HBW among First Nations women. There was a significant interaction effect between pre-gestational weight 91kg and GDM for very HBW. The OR for very HBW in women with both GDM and pre-gestational weight 91kg was 5.07 (95% CI 3.73, 6.89) compared to women
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Table 1. Average annual percent change (AAPC) in the age-adjusted prevalence of birth weight categories among pregnancies in Alberta, 2000-2009 (n [ 426 945). Values are AAPCs (95% CI) First Nations (n ¼ 28 286)
Non-First Nations (n ¼ 398 659)
High birth weight
2.1 (3.3, 0.8)
2.4 (2.8, 2.1)
Very high birth weight
0.3 (2.3, 1.8)
3.6 (5.0, 2.1)
Low birth weight
0.7 (1.6, 3.0)
1.1 (0.6, 1.6)
Very low birth weight
0.2 (3.0, 3.6)
0.7 (0.7, 2.1)
without GDM and without weight 91kg. Thus, there is an additive effect of pre-gestational weight 91kg and GDM on very HBW. Smoking, illicit drug dependence, and alcohol consumption were negatively associated with HBW. Potentially manageable risk factors for LBW included pregestational renal disease, hypertension, and maternal weight 45 kg, as well as smoking, illicit drug dependence, and alcohol consumption. Pre-gestational maternal weight 91 kg was negatively associated with LBW.
DISCUSSION
Our study confirms an increased prevalence and risk of HBW in First Nations populations compared to nonAboriginal populations.2,7e9 We report the same 82% increased risk of HBW after adjustment for other predictors as was shown by systematic review and metaanalysis for Canadian Aboriginal populations compared to non-Aboriginal populations.2 Much of the epidemiology of HBW in First Nations has been examined among the James Bay Cree populations of northern Quebec, with rates of 34.3%,7 36.5%,10 37.2%,11 and 36.1%12 being reported. Little is known about the prevalence of HBW in western provinces. Our observed rate of HBW in First Nations in Alberta (17.7%) is considerably lower, and similar to that reported in First Nations in Manitoba (20.1%).8 That the prevalence of GDM is notably lower among Alberta (6.1%)1 and Manitoba (6.9%)8 First Nations compared to the prevalence among the James Bay Cree (18.6%)11 may partly explain the lower risk of HBW. GDM has been shown to be a strong risk factor for HBW in First Nations populations,7,8,10 as has maternal
Table 2. Significant adjusted multivariate predictors of birth weight categories among First Nations women in Alberta (n [ 28 286). Values are odds ratios (95% CI) Age 17*
HBW (n ¼ 4903)
Very HBW (n ¼ 1075)
-
-
LBW (n ¼ 2206) 0.76 (0.62, 0.94)
Very LBW (n ¼ 640) -
Age 35*
-
-
1.61 (1.39, 1.87)
1.48 (1.16, 1.90)
Parity (0)†
-
-
1.07 (1.02, 1.13)
-
Male sex
1.45 (1.36, 1.54)
1.62 (1.42, 1.84)
-
-
Multiple gestation
-
-
16.31 (14.00, 19.00)
8.93 (7.18, 11.12)
Chronic renal disease
-
-
3.18 (1.23, 8.18)
7.80 (2.72, 22.40)
Pre-existing hypertension
-
-
3.44 (2.39, 4.94)
2.45 (1.35, 4.44)
Gestational diabetes mellitus
1.70 (1.49, 1.94)
2.18 (1.77, 2.68)§
Pre-gestational weight 45kg
-
-
1.82 (1.010-2.99)
-
Pre-gestational weight 91kg
2.32 (2.14, 2.53)
2.76 (2.40, 3.18)§
0.54 (0.46, 0.64)
0.52 (0.39, 0.71)
Drug dependant
0.56 (0.47, 0.67)
0.63 (0.44, 0.89)
2.05 (1.76, 2.39)
1.64 (1.24, 2.16)
Smoker
0.66 (0.62, 0.71)
0.62 (0.54, 0.70)
1.29 (1.17, 1.43)
-
Alcohol
0.88 (0.78, 0.99)
-
1.45 (1.26, 1.67)
1.34 (1.05, 1.72)
History of abortion
-
-
1.40 (1.20, 1.63)
2.03 (1.61, 2.55)
History of neonatal death
0.65 (0.44, 0.95)
-
1.55 (1.11, 2.17)
2.35 (1.47, 3.78)
History of stillbirth
0.72 (0.56, 0.93)
-
2.18 (1.73, 2.74)
3.05 (2.18, 4.27)
History of preterm
0.77 (0.71, 0.83)
0.72 (0.61, 0.84)
1.76 (1.59, 1.94)
1.30 (1.09, 1.55)
History of LGA
4.48 (3.74, 5.38)
5.88 (4.69, 7.36)
0.29 (0.16, 0.52)
-
History of SGA
0.41 (0.23, 0.75)
-
3.64 (2.60, 5.09)
-
History of Caesarean section
0.82 (0.74, 0.91)
-
1.24 (1.09, 1.42)
-
LGA: large for gestational age; SGA: small for gestational age. *Compared to age 18-34. †
Compared to parity ¼ 1 or 2.
§
Significant interaction effect between pregestational weight 91kg and gestational diabetes.
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-
-
Longitudinal Rates and Risk Factors for Adverse Birth Weight Among First Nations Pregnancies in Alberta
obesity.10,11,13 Our large dataset and access to numerous potential confounders allowed for robust multivariable logistic regression analyses, showing for the first time a significant additive effect of both maternal GDM and maternal obesity on very HBW risk in First Nations infants. Such women were five times more likely to have a very HBW infant. We were encouraged by the significant decrease in HBW and stability of very HBW longitudinally among infants born to First Nations women in Alberta. To our knowledge, the only other examination of trends in a Canadian Aboriginal population has been in a recent study of Quebec First Nations. In this group, a slight upward trend was observed for HBW rates; the rates were approximately 18.2% in 1981-1989 and 19.8% in 2000-2008.9 In the same study, inequalities in very HBW between First Nations and non-First Nations expanded as rates increased for First Nations from approximately 5.4% to 7.5%.9 In Alberta, the prevalence of GDM has not increased for First Nations women between the years 2000 and 2009,1 perhaps explaining to some degree the lack of increase in HBW and very HBW. Our finding that First Nations ethnicity is not a predictor of LBW after adjusting for confounders supports data from the same recent systematic review and meta-analysis, which found no increased risk of LBW for Canadian Aboriginal populations compared to the non-Aboriginal population.2 We also show that in contrast to the nonFirst Nations population, LBW is not increasing in Alberta First Nations, which supports data from northern Quebec First Nations where no increase was seen over a 10 year period.14 However, rates appear to be higher in Alberta (8.8%) than in British Columbia Bella Coola First Nations (5%)15 and northern Quebec Cree First Nations (2.4%).10 Our study is the first to examine very LBW in a First Nation population, and the first to examine longitudinal trends in very LBW in an Indigenous group. We found First Nations infants were significantly more likely to have very LBW compared to non-First Nations, yet rates have not increased over time. In contrast, data from the early 2000s in the United States showed no difference in the prevalence of very LBW among American Indians (1.3%) and their Caucasian counterparts (1.2%).16 For the general population of Alberta we report significant decreases in HBW and very HBW longitudinally. This supports data from large national studies, including National Center for Health Statistics data in the United States suggesting that overall birth weights have decreased (by 52g) between 1990 and 2005 in the United States17 and Canadian Vital Statistics data indicating a decrease in HBW
prevalence (from 16.8% to 14.4% among infant males and 10.6% to 8.8% among infant females between 2000 and 2007).18 This decrease in HBW despite continued increases in rates of obesity and diabetes,19,20 and falling smoking rates,21 cannot be explained by our study and requires further investigation. It has been suggested that declines in gestational age at birth may partly explain the declines in HBW.17 However, trends are not consistent across nonAboriginal populations in Canada, because the prevalence of HBW actually increased significantly from 16.2% to 17.5% between 1992 and 2005 in Newfoundland and Labrador22 and from 7.1% to 9.2% between 1981-1989 and 2000-2008 in Quebec.9 Canada has the lowest national rate of LBW of the G7 nations,23 but rates remain higher than those in Scandinavian nations.18 In the 2012 general Canadian population, LBW occurred in approximately 6.2% births nationally; rates have remained relatively stable over the past three decades based on Vital Statistics data.23 However, geographical differences are apparent, as we report a slightly higher prevalence of LBW among the general Alberta population (7.1%), with rates increasing over time. Similarly, Simonet et al.14 found the rate of LBW increased between 1991 and 2000 from 5.5% to 7.6% in nonAboriginal communities in northern Quebec. The observed ethnic (First Nations vs. non-First Nations) disparities may be underestimated. Our findings cannot be generalized to non-registered First Nations individuals and Métis individuals, as these individuals could not be identified and were included in the non-First Nations population group. The contributions of access to health care, lifestyle, gestational weight gain, social environment, socioeconomic status, and other potential contextual predictors to the logistic regression models could not be assessed. We hypothesize that ethnic disparities in these factors likely contributed to the increased risk of various birth weight categories in the First Nations infants. CONCLUSION
Our study is the first to rigorously explore the age-adjusted prevalence of birth weight categories longitudinally in a First Nations population. Although HBW, very HBW, and very LBW remain more common in Alberta First Nations than in non-First Nations, it is encouraging that their prevalence is not increasing. Earlier and better management of both maternal obesity and GDM in First Nations women could lead to less HBW infants. Strategies to decrease LBW risk should aim to reduce smoking, illicit drug dependence, and alcohol consumption among pregnant First Nations women, and to improve pre-gestational
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renal disease and the identification and management of hypertension. ACKNOWLEDGEMENTS
This study was funded in part by the Canadian Institutes for Health Research, Institute of Aboriginal Peoples Health. This study is based on data provided by the APHP and Alberta Health. The interpretation and conclusions contained herein are those of the researchers and do not necessarily represent those of the Alberta Perinatal Health Program, Alberta Health, or the Government of Alberta. Neither the Alberta Perinatal Health Program, nor Alberta Health, nor the Government of Alberta expresses any opinion in relation to this study. REFERENCES 1. Oster RT, King M, Morrish DW, Mayan MJ, Toth EL. Diabetes in pregnancy among First Nations women in Alberta, Canada: a retrospective analysis. BMC Pregnancy Childbirth 2014;14:136.
9. Auger N, Park AL, Zoungrana H, Fon Sing M, Lo E, Luo ZC. Widening inequality in extreme macrosomia between Indigneous and non-Indigenous populations of Quebec, Canada. Aust N Z J Public Health 2013;37(1):58e62. 10. Willows ND, Sanou D, Bell RC. Assessment of Canadian Cree infants’ birth size using the WHO Child Growth Standards. Am J Hum Biol 2011;23(1):126e31. 11. Brennand EA, Dannenbaum D, Willows ND. Pregnancy outcomes of First Nations women in relation to pregravid weight and pregnancy weight gain. J Obstet Gynaecol Can 2005;27(10):936e44. 12. Armstrong IE, Robinson EJ, Gray-Donald K. Prevalence of low and high birthweight among the James Bay Cree of northern Quebec. Can J Public Health 1998;89(6):419e20. 13. Oliveira AP, Kalra S, Wahi G, McDonald S, Desai D, Wilson J, et al. Maternal and newborn health profile in a First Nations community in Canada. J Obstet Gynaecol Can 2013;35(10):905e13. 14. Simonet F, Wilkins R, Luo ZC. Temporal trends in Inuit, First Nations and non-Aboriginal birth outcomes in rural and northern Quebec. Int J Circumpolar Health 2012;71. 15. Thommasen HV, Klein MC, Mackenzie T, Grzybowski S. Perinatal outcomes at Bella Coola general hospital: 1940 to 2001. Can J Rural Med 2005;10(1):22e8. 16. Mathews TJ, Menacker F, MacDorman MF. Centers for Disease Control and Prevention, National Center for Health Statistics. Infant mortality statistics from the 2002 period: linked birth/infant death data set. Natl Vital Stat Rep 2004;53(10):1e29.
2. Shah PR, Zao J, Al-Wassia H, Shah V. Knowledge Synthesis Group on Determinants of Preterm/LBW Births. Pregnancy and neonatal outcomes of Aboriginal women: a systematic review and meta-analysis. Womens Health Issues 2011;21(1):28e39.
17. Donahue SM, Kleinman KP, Gillman MW, Oken E. Trends in birth weight and gestational length among singleton term births in the United States: 1990-2005. Obstet Gynecol 2010;115(2 Pt 1):357e64.
3. Barker DJ, Winter PD, Osmond C, Margetts B, Simmonds SJ. Weight in infancy and death from ischaemic heart disease. Lancet 1989;2(8663):577e80.
18. Health Canada. The Well-being of Canada’s Young Children. Available at: www.dpe-agje-ecd-elcc.ca/eng/ecd/well-being/sp_1027_04_12_eng.pdf; 2011. Accessed March 8, 2015.
4. Oster RT, Luyckx VA, Toth EL. Birth weight predicts both proteinuria and overweight/obesity in a rural population of Aboriginal and non-Aboriginal Canadians. J Dev Orig Health Dis 2013;4(2):139e45.
19. Twells LK, Gregory DM, Reddigan J, Midodzi WK. Current and predicted prevalence of obesity in Canada: a trend analysis. CMAJ Open 2014;2(1):E18e26.
5. Statistics Canada. National Households Survey, 2011. Aboriginal Peoples in Canada: First Nations people, Métis, and Inuit. Available at: http://www12. statcan.gc.ca/nhs-enm/2011/as-sa/99-011-x/99-011-x2011001-eng.pdf; 2011. Accessed February 26, 2015.
20. Oster RT, Johnson JA, Hemmelgarn B, King M, Balko SU, Svenson L, et al. Recent epidemiologic trends of diabetes mellitus among status Aboriginal adults. CMAJ 2011;183(12):E803e8.
6. Bursac Z, Gauss CH, Williams DK, Hosmer DW. Purposeful selection of variables in logistic regression. Source Code Biol Med 2008;3:17.
21. Reid JL, Hammond D, Burkhalter R, Rynard VL, Ahmed R. Tobacco Use in Canada: Patterns and Trends. Waterloo, ON: Propel Centre for Population Health Impact, University of Waterloo; 2013 Edition.
7. Rodrigues S, Robinson EJ, Kramer MS, Gray-Donald K. High rates of infant macrosomia: A comparison of a Canadian native and a non-native population. J Nutr 2000;130:806e12.
22. Edwards NM, Audas RP. Trends of abnormal birthweight among full-term infants in Newfoundland and Labrador. Can J Public Health 2010;101(2):138e42.
8. Aljohani N, Rempel BM, Ludwig S, Morris M, McQuillen K, Cheang M, et al. Gestational diabetes in Manitoba during a twenty-year period. Clin Invest Med 2008;31(3):E131e7.
23. Employment and Social Development Canada. Indicators of Well-being in Canada. Available at: http://well-being.esdc.gc.ca/misme-iowb/.3ndic.1t.4 [email protected]?iid¼4; 2011. Accessed March 31, 2015.
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