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Reducing perinatal mortality among Indigenous babies in Queensland: should the first priority be better primary health care or better access to hospital care during confinement?

Reducing perinatal mortality among Indigenous babies in Queensland: should the first priority be... Background: The perinatal mortality rate among Indigenous Australians is still double that of the rest of the community. The aim of our study was to estimate the extent to which increased risk of low birthweight and preterm birth among Indigenous babies in Queensland account for their continuing mortality excess. If a large proportion of excess deaths can be explained by the unfavourable birthweight and gestational age distribution of Indigenous babies, then that would suggest that priority should be given to implementing primary health care interventions to reduce the risk of low birthweight and preterm birth (eg, interventions to reduce maternal smoking or genitourinary infections). Conversely, if only a small proportion is explained by birthweight and gestational age, then other strategies might need to be considered such as improving access to high- quality hospital care around the time of confinement. Methodology: Population-based, descriptive study of perinatal mortality rates among Indigenous and non-Indigenous babies, in Queensland, stratified by birthweight and gestational age. Results: Indigenous babies are twice as likely to die as their non-Indigenous counterparts (rate ratio1998–2002: 2.01; 95%ci 1.77, 2.28). However, within separate strata of birth weight and gestational age, Indigenous and non-Indigenous rates are similar. The Mantel-Haenszel rate ratio adjusted for birth weight and gestational age was 1.13 (0.99, 1.28). This means that most of the excess mortality in Indigenous babies is largely due to their unfavourable birth weight and gestational-age distributions. If Indigenous babies had the same birth weight and gestational age distribution as their non-Indigenous counterparts, then the relative disparity would be reduced by 87% and 20 fewer Indigenous babies would die in Queensland each year. Conclusion: Our results suggest that Indigenous mothers at high risk of poor outcome (for example those Indigenous mothers in preterm labour) have good access to high quality medical care around the time of confinement. The main reason Indigenous babies have a high risk of death is because they are born too early and too small. Thus, to reduce the relative excess of deaths among Indigenous babies, priority should be given to primary health care initiatives aimed at reducing the prevalence of low birth weight and preterm birth. Page 1 of 5 (page number not for citation purposes) Australia and New Zealand Health Policy 2005, 2:11 http://www.anzhealthpolicy.com/content/2/1/11 of identifying policy issues, setting agendas, and facilitat- Background From a public-health perspective, the major obstetric and ing discussion. perinatal problem in Australia is the poor health of Indig- enous mothers and babies. Although Australia as a whole To be more specific, if a large proportion of excess deaths has one of the lowest perinatal mortality rates (PMR) of can be explained by the unfavourable birthweight and any of the established market economies [1], Indigenous gestational age distribution of Indigenous babies, then Australians have PMRs that are at least twice as high as that would suggest that priority should be given to imple- their non-Indigenous counterparts [2,3]. menting primary health care interventions to reduce the risk of low birthweight and preterm birth (eg, interven- Moreover, the relative excess of deaths among Indigenous tions to reduce maternal smoking or genitourinary infec- babies has not improved over time. In Queensland in tions). Conversely, if only a small proportion is explained 1987–1989, the PMR was 2.2 times higher among Indige- by birthweight and gestational age, then other strategies nous compared with non-Indigenous babies and in might need to be considered such as improving access to 2000–2002 the rate was still 2.1 times higher. A similar high-quality hospital care around the time of lack of progress is evident in other states [4-6]. confinement. The risk of perinatal death is strongly related to a baby's Methods birthweight and gestational age. For example, the risk of Data were obtained from the population-based Queens- death for a moderately preterm baby (33 to 36 weeks ges- land Perinatal Data Collection for the five years 1998 to tation) in Queensland is 8.2 times greater than that of a 2002. This was the most recent five-year period for which term baby and for a very preterm baby (27 to 32 weeks) complete data were available. The database includes infor- the risk is 41.3 times greater. Similarly, a baby who was mation on all livebirths and stillbirths of at least 20 weeks born at term but weighed less than 2500 g was 6.3 times gestation or 400 g birthweight. A perinatal death is more likely to die than a baby who weighed more than defined as a stillbirth or the death of a liveborn baby 2500 g. In Queensland, Indigenous babies are 1.6 (95%ci: within 28 days of birth. Our data set comprised 231,039 1.5,1.7) times more likely to be born preterm (<37 weeks births and 2,255 deaths to non-Indigenous mothers and gestation) and 2.2 (2.0,2.5) times more likely to be low 13,920 births and 273 deaths to Indigenous mothers. birthweight at term than non-Indigenous babies [3]. Sim- Indigenous status is based on the self-reported Indigenous ilar disparities in birthweight and gestational age have status of the mother and the gestational age is based on been reported from the other states of Australia [2,5,7-10]. the best clinical estimate, which might be derived from the date of the last menstrual period, ultrasound in early The aim of this paper is to estimate the number and pro- pregnancy or maturity scoring of the neonate at birth. The portion of excess deaths among Indigenous babies that method used is not recorded. can be explained by their higher risk of low birthweight and preterm birth. This analysis strategy assumes that the In this paper we report the results of a Mantel-Haenszel distribution of birthweight and gestational age among procedure, which was used to determine the relationship Indigenous babies reflects the prevalence of antenatal risk between perinatal mortality and Indigenous status factors such as smoking, infection, maternal nutrition and adjusted for the effect of low birthweight and preterm psycho-social stress; while any excess of mortality that birth. The proportion and number of deaths that could be remains after the excess low-birthweight and preterm risk avoided were estimated by comparison of the crude and among Indigenous babies is removed might say some- adjusted rates. thing about the quality of medical care at the time of confinement. We also used Poisson-regression models to adjust perina- tal mortality rates for birthweight and gestational age. We Although such reasoning has many proponents [11-13], variously fitted single week or four week categories of ges- risk factors such as smoking and infection are likely to also tational age and 250 g and 500 g categories of birth have at least a small effect on mortality that is independ- weight. The results were the same as using the Mantel- ent of birthweight and gestational age. That is, adjustment Haenzel approach with broad categories of gestational age of perinatal mortality rates by birthweight and gestational and birthweight, and we included these in preference to age is not a perfect way of assessing the quality of medical the Poisson-regression models for ease of interpretation. care at the time of confinement. It is similar to case-mix adjustments used in other settings to allow for differences Results in risk [14,15]. Such adjustments are not expected to The crude perinatal mortality rate among Indigenous remove all confounding. Instead, the reasoning is that the babies was 19.6 per 1000 births, which was 2.01 adjusted rates, although not perfect, provide a useful way (95%ci:1.77,2.28) times higher than the rate among non- Page 2 of 5 (page number not for citation purposes) Australia and New Zealand Health Policy 2005, 2:11 http://www.anzhealthpolicy.com/content/2/1/11 Perinatal mortality rate ratio Born prior to 28 weeks 1.02 (0.86-1.21) Born 28-36 weeks 1.24 (0.94-1.62) Born 37+ weeks, weight <2500g 0.94 (0.41-1.88) Born 37+ weeks, weight >2500g 1.55 (1.09-2.14) Crude overall RR 2.01 (1.77-2.28) Mantel-Haenszel combined RR 1.13 (0.99-1.28) Source: Queensland Perinatal Data Collection 2 Figure 1 Rate ratios 002 comparing Indigenous to non-Indigenous perinatal mortality stratified by preterm and birthweight status, 1998– Rate ratios comparing Indigenous to non-Indigenous perinatal mortality stratified by preterm and birthweight status, 1998– 2002. a) Rate ratios greater than 1.0 indicate higher mortality among Indigenous babies. b) Differences between stratum-spe- cific rate ratios are not statistically significant (χ (3) = 5.78, p = 0.1226). Indigenous babies. When perinatal mortality rates were is adequate for Indigenous mothers and babies. That is, compared within each birthweight and gestational age priority should initially be given to primary health care strata, the point estimates suggested that Indigenous interventions to reduce the proportion of preterm and low babies were only slightly more likely to die than non- birth weight babies. Indigenous babies (Figure 1). The test for homogeneity of the rate ratios across strata was not significant (χ (3) = Policy implications 5.78, p = 0.1226) suggesting that the effect of Indigenous Risk factors for preterm birth and low birth weight include status is the same across the birthweight and gestational smoking, gentio-urinary tract infections, poor maternal age strata (except for statistical noise) and that it is appro- nutrition and psycho-social stress [16-19]. Several studies priate to use the adjusted combined estimate: M-H have reported a higher prevalence of these risk factors Adjusted RR = 1.13, 0.99–1.28. among Indigenous compared with non-Indigenous mothers. These results suggest that if the population of Indigenous babies had the same birthweight and gestational age dis- More specifically, the prevalence of smoking among tribution as non-Indigenous babies, then the relative dis- Indigenous women during pregnancy has been reported parity would be reduced by 87% and there would be 20 to be more than 60%, which is at least 3 times the preva- fewer deaths of Indigenous babies per year. lence for non-Indigenous women [9,20,21]. A recent Cochran review found that there are effective primary Discussion health care interventions to help and support women to Interpretation of results stop smoking that lead to fewer preterm babies and better Perinatal mortality among Indigenous babies has birthweights [22]. Further, we know that Indigenous remained twice that of their non-Indigenous counterparts women are more than two times as likely to have a urinary for more than a decade. We found that most of this mor- tract infection during pregnancy as non-Indigenous tality excess is because Indigenous babies are at greater women [23]. In overseas studies, primary health care risk of being born too early and too small. In contrast, the interventions to detect and treat asymptomatic bacteruria case fatality rates of Indigenous babies who were born pre- have been shown to decrease preterm birth by 40% [24]. term or of low birth weight were similar to their non- Indigenous counterparts. In Australia, the best example we have of a primary health care initiative aimed at reducing risk factors among Indig- Using a framework advocated by several perinatal epide- enous mothers is the Strong Women Strong Babies Strong miologists [11-13], these results suggests that, broadly Culture program in the Northern Territory [25]. This pro- speaking, access to high quality care during confinement gram resulted in increased early attendance for antenatal Page 3 of 5 (page number not for citation purposes) Australia and New Zealand Health Policy 2005, 2:11 http://www.anzhealthpolicy.com/content/2/1/11 care, reduced numbers of STDs and a reduced proportion of the mortality excess for Indigenous people and pro- of low birthweight babies [26]. vides robust support for policy discussions. Although such results are encouraging, if substantial For several reasons, gestational age is known to be less progress is to be made across the whole of Australia, a accurate among Indigenous than non-Indigenous babies properly funded national initiative is needed. Such an ini- [31]. Nevertheless, previous work in Queensland and else- tiative would include funding to improve access to cultur- where has shown that gestational age in combination ally appropriate primary health care during the antenatal with birthweight provides a better statistical adjustment of period, which would deliver, inter alia, interventions for mortality rates than birthweight alone [32,33]. We there- smoking cessation, screening and treatment of genito-uri- fore considered it better to present birthweight and gesta- nary tract infections, screening for domestic violence, and tional age adjusted rates, rather than just birthweight- programs aimed at reducing alcohol consumption and adjusted rates. poor nutrition. Conclusion Although perinatal mortality rates in Queensland have It would not be a case of one strategy fits all. Instead local partnerships with possibly different types of service mod- decreased over the last 16 years, the rates in Indigenous els would be needed to implement the national initiative. populations remain at least double those in the non- This approach will encourage creativity, innovation and Indigenous population. Our analyses, stratified by birth- risk taking, which will be essential ingredients to tackling weight and gestational age, suggest that the priority for a situation that has proved difficult to improve. reducing the excess mortality among Indigenous babies is primary health care to reduce the prevalence of risk factors Study limitations during the antenatal period. A primary health care Using vital statistics to set agendas has a long and contin- approach encompasses a much-needed component of an uing tradition in public health [27]. The advantages of overall shift towards empowerment of Indigenous such statistics are convenience, low cost and total enumer- women and increased awareness and ownership of health ation. The disadvantages are insufficient and inaccurate which has the potential to play an important role in data, which create uncertainty about the validity of the reducing the social inequality that has resulted in out- results [27]. This study used four variables: perinatal comes such as those found for perinatal mortality. death, birthweight, gestational age, and Indigenous status. It is unlikely that an important number of perinatal Authors' contributions deaths were missed because they are checked against noti- TJ performed the statistical analysis and participated in fications to the Registrar-General of Births, Deaths and drafting the manuscript. MC conceived of the study and Marriages. It is also unlikely that there are important its design and participated in drafting the manuscript. errors in the measurement of birthweight. Consequently, Both authors read and approved the final manuscript. the main areas of uncertainty are Indigenous status and gestational age. References 1. OECD: OECD Health Data. . 2. ABS, AIHW: The health and welfare of Australia's Aboriginal With regard to Indigenous status, some mothers may be and Torres Strait Islander Peoples. Canberra , ABS and AIHW; reluctant to identify as Indigenous, others may be non- 2003. 3. Johnston T, Coory M: Trends in perinatal mortality, birth- Indigenous with an Indigenous male partner, or midwives weight and gestational age among Aboriginal, Torres Strait may not ask the mother or make an educated guess [28]. Islander and non-Indigenous babies in Queensland. In Informa- tion Circular No 67 Brisbane , Epidemiology Services Unit, Health Infor- However, of all the types of mortality data, perinatal mor- mation Branch, Queensland Health; 2004. tality provides the most accurate estimate of excess Indig- 4. Roder D, Chan A, Priest K: Perinatal mortality trends among enous mortality because the numerator (number of South Australian Aboriginal births 1981-92. Journal of Paediatric Child Health 1995, 31:446-450. perinatal deaths) and denominator (number of births) for 5. Gee V, Green TJ: Perinatal Statistics in Western Australia, the rate can be obtained from the one data set. This is in 2002: Twentieth Annual Report of the Western Australian contrast to adult death rates where identification of Indig- Midwives' Notification System. Perth , Department of Health; enous people can be different in death registration data 6. Alessandri LM, Chambers HM, Blair EM, Read AW: Perinatal and (the numerator for mortality rates) and population data postneonatal mortality among Indigenous and non-Indige- nous infants born in Western Australia, 1980-1998. Medical (the denominator). This problem of the numerator not Journal of Australia 2001, 175:185-189. being appropriate for the denominator is not unique to 7. Riley M, King J: Births in Victoria 2001-2002. Melbourne , Victo- comparisons of Indigenous and non-Indigenous Austral- rian Perinatal Data Collection Unit, Victorian Government Depart- ment of Human Services; 2003. ians; it hinders interpretation of race-specific rates around 8. NT Perinatal Information Managment Group: Northern Territory the world [29,30]. Thus, of all the routinely available mor- Midwives Collection: Mothers and Babies 1999. Darwin , Department of Health and Community Services; 2002. tality data, perinatal data provides the most valid estimate Page 4 of 5 (page number not for citation purposes) Australia and New Zealand Health Policy 2005, 2:11 http://www.anzhealthpolicy.com/content/2/1/11 9. NSW Department of Health: The NSW Aboriginal perinatal 33. Wilcox AJ: On the importance - and the unimportance - of health report. Sydney , NSW Department of Health; 2003. birthweight. International Journal of Epidemiology 2001, 10. Westenberg L, van der Klis K, Chan A, Dekker G, Keane RJ: Aborig- 30:1233-1241. inal teenage pregnancies compared with non-Aboriginal in South Australia 1995-1999. Australian and New Zealand Journal of Obstetrics and Gynaecology 2002, 42(2):187-192. 11. Clarke M, Mason ES, MacVicar J, Clayton DG: Evaluating perinatal mortality rates: Effects of referral and case mix. British Medical Journal 1993, 306:824-827. 12. Macfarlane A, Mugford M, Johnson A, Garcia J: Counting the changes in childbirth: Trends and gaps in national statistics. Oxford , National Perinatal Statistics Unit; 1996. 13. Joyce R, Peacock J: A comparison of methods of adjusting still- birth and neonatal mortality rates for birthweight in hospital and geographic populations. Paediatric Perinatal Epidemiology 2003, 17:119-124. 14. Iezzoni L: Assessing quality using administrative data. Annals of Internal Medicine 1997, 127:666-674. 15. Coory M, Youlden D, Baker P: Interpretation of hospital-specific outcome measures based on routine data. Australian Health Review 2002, 25:69-72. 16. Kramer MS: The epidemiology of adverse pregnancy out- comes: An overview. Journal of Nutrition 2003, 133(5 Supp 2):S1592-S1596. 17. Gulmezoglu AM, de Onis M, Villar J: Effectiveness of interven- tions to prevent or treat impaired fetal growth. Obstetrical and Gynecological Survey 1997, 52(2):139-148. 18. Villar J, Gulmezoglu AM, de Onis M: Nutritional and antimicro- bial interventions to prevent preterm birth: An overview of randomized controlled trials. Obstetrical and Gynecological Survey 1998, 53(9):575-585. 19. Goldenberg RL, Rouse DJ: Prevention of premature birth. The New England Journal of Medicine 1998, 339(5):313-320. 20. Chan A, Keane RJ, Robinson JS: The contribution of maternal smoking to preterm birth, small for gestational age and low birthweight among Aboriginal and non-Aboriginal births in South Australia. Medical Journal of Australia 2001, 174:389-393. 21. Gilchrist D, Woods B, Binns CW, Scott JA, Gracey M, Smith H: Abo- riginal mothers, breastfeeding and smoking. Australian and New Zealand Journal of Public Health 2004, 28(3):225--228. 22. Lumley J, Oliver SS, Chamberlain C, Oakley L: Interventions for promoting smoking cessation during pregnancy (Review). The Cochrane Library 2005, 2005(1):. 23. de Costa C, Child A: Pregnancy outcomes in urban Aboriginal women. Medical Journal of Australia 1996, 164:523-526. 24. Darmstadt GL, Bhutta ZA, Cousens S, Adam T, Walker N, de Bernis L: Evidence-based, cost-effective interventions: how many newborn babies can we save? Lancet 2005, March 3:. 25. Herceg A: Improving health in Aboriginal and Torres Strait Islander pregnant women, babies and young children: A lit- erature review: 15-16 September 2004; Canberra. Volume 10. Edited by: Sansoni J, Tilley L. The Australian Health Outcomes Collaboration; 2004. 26. Mackerras D: Birthweight changes in the pilot phase of the Strong Women Strong Babies Strong Culture Program in the Northern Territory. Australian and New Zealand Journal of Pub- lic Health 2001, 25(1):34-40. 27. Gould JB: Vital records for quality improvements. Pediatrics 1999, 103:278-290. 28. Robertson H, Lumley J: How midwives identify women as Abo- riginal or Torres Strait Islanders. Australian College of Widwives Publish with Bio Med Central and every Journal 1995:26-29. scientist can read your work free of charge 29. Paradies Y, Cunningham J: Placing Aboriginal and Torres Strait Islander mortality in an international context. Australian and "BioMed Central will be the most significant development for New Zealand Journal of Public Health 2002, 26(1):11-16. disseminating the results of biomedical researc h in our lifetime." 30. Kaufman J: How inconsistencies in racial classification demys- Sir Paul Nurse, Cancer Research UK tify the race construct in public health statistics. Epidemiology 1999, 10:101-103. Your research papers will be: 31. Day P, Sullivan EA, Lancaster P: Indigenous mothers and their available free of charge to the entire biomedical community babies. In Perinatal Statistical Series No 8 Sydney , AIHW National Perinatal Statistics Unit; 1999. peer reviewed and published immediately upon acceptance 32. Coory M: Does gestational age in combination with birth- cited in PubMed and archived on PubMed Central weight provide a better statistical adjustment of neonatal mortality rates than birthweight alone? Paediatric Perinatal yours — you keep the copyright Epidemiology 1997, 11:385-391. BioMedcentral Submit your manuscript here: http://www.biomedcentral.com/info/publishing_adv.asp Page 5 of 5 (page number not for citation purposes) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Australia and New Zealand Health Policy Springer Journals

Reducing perinatal mortality among Indigenous babies in Queensland: should the first priority be better primary health care or better access to hospital care during confinement?

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Springer Journals
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Copyright © 2005 by Johnston and Coory; licensee BioMed Central Ltd.
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Medicine & Public Health; Public Health; Social Policy
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1743-8462
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10.1186/1743-8462-2-11
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15918912
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Abstract

Background: The perinatal mortality rate among Indigenous Australians is still double that of the rest of the community. The aim of our study was to estimate the extent to which increased risk of low birthweight and preterm birth among Indigenous babies in Queensland account for their continuing mortality excess. If a large proportion of excess deaths can be explained by the unfavourable birthweight and gestational age distribution of Indigenous babies, then that would suggest that priority should be given to implementing primary health care interventions to reduce the risk of low birthweight and preterm birth (eg, interventions to reduce maternal smoking or genitourinary infections). Conversely, if only a small proportion is explained by birthweight and gestational age, then other strategies might need to be considered such as improving access to high- quality hospital care around the time of confinement. Methodology: Population-based, descriptive study of perinatal mortality rates among Indigenous and non-Indigenous babies, in Queensland, stratified by birthweight and gestational age. Results: Indigenous babies are twice as likely to die as their non-Indigenous counterparts (rate ratio1998–2002: 2.01; 95%ci 1.77, 2.28). However, within separate strata of birth weight and gestational age, Indigenous and non-Indigenous rates are similar. The Mantel-Haenszel rate ratio adjusted for birth weight and gestational age was 1.13 (0.99, 1.28). This means that most of the excess mortality in Indigenous babies is largely due to their unfavourable birth weight and gestational-age distributions. If Indigenous babies had the same birth weight and gestational age distribution as their non-Indigenous counterparts, then the relative disparity would be reduced by 87% and 20 fewer Indigenous babies would die in Queensland each year. Conclusion: Our results suggest that Indigenous mothers at high risk of poor outcome (for example those Indigenous mothers in preterm labour) have good access to high quality medical care around the time of confinement. The main reason Indigenous babies have a high risk of death is because they are born too early and too small. Thus, to reduce the relative excess of deaths among Indigenous babies, priority should be given to primary health care initiatives aimed at reducing the prevalence of low birth weight and preterm birth. Page 1 of 5 (page number not for citation purposes) Australia and New Zealand Health Policy 2005, 2:11 http://www.anzhealthpolicy.com/content/2/1/11 of identifying policy issues, setting agendas, and facilitat- Background From a public-health perspective, the major obstetric and ing discussion. perinatal problem in Australia is the poor health of Indig- enous mothers and babies. Although Australia as a whole To be more specific, if a large proportion of excess deaths has one of the lowest perinatal mortality rates (PMR) of can be explained by the unfavourable birthweight and any of the established market economies [1], Indigenous gestational age distribution of Indigenous babies, then Australians have PMRs that are at least twice as high as that would suggest that priority should be given to imple- their non-Indigenous counterparts [2,3]. menting primary health care interventions to reduce the risk of low birthweight and preterm birth (eg, interven- Moreover, the relative excess of deaths among Indigenous tions to reduce maternal smoking or genitourinary infec- babies has not improved over time. In Queensland in tions). Conversely, if only a small proportion is explained 1987–1989, the PMR was 2.2 times higher among Indige- by birthweight and gestational age, then other strategies nous compared with non-Indigenous babies and in might need to be considered such as improving access to 2000–2002 the rate was still 2.1 times higher. A similar high-quality hospital care around the time of lack of progress is evident in other states [4-6]. confinement. The risk of perinatal death is strongly related to a baby's Methods birthweight and gestational age. For example, the risk of Data were obtained from the population-based Queens- death for a moderately preterm baby (33 to 36 weeks ges- land Perinatal Data Collection for the five years 1998 to tation) in Queensland is 8.2 times greater than that of a 2002. This was the most recent five-year period for which term baby and for a very preterm baby (27 to 32 weeks) complete data were available. The database includes infor- the risk is 41.3 times greater. Similarly, a baby who was mation on all livebirths and stillbirths of at least 20 weeks born at term but weighed less than 2500 g was 6.3 times gestation or 400 g birthweight. A perinatal death is more likely to die than a baby who weighed more than defined as a stillbirth or the death of a liveborn baby 2500 g. In Queensland, Indigenous babies are 1.6 (95%ci: within 28 days of birth. Our data set comprised 231,039 1.5,1.7) times more likely to be born preterm (<37 weeks births and 2,255 deaths to non-Indigenous mothers and gestation) and 2.2 (2.0,2.5) times more likely to be low 13,920 births and 273 deaths to Indigenous mothers. birthweight at term than non-Indigenous babies [3]. Sim- Indigenous status is based on the self-reported Indigenous ilar disparities in birthweight and gestational age have status of the mother and the gestational age is based on been reported from the other states of Australia [2,5,7-10]. the best clinical estimate, which might be derived from the date of the last menstrual period, ultrasound in early The aim of this paper is to estimate the number and pro- pregnancy or maturity scoring of the neonate at birth. The portion of excess deaths among Indigenous babies that method used is not recorded. can be explained by their higher risk of low birthweight and preterm birth. This analysis strategy assumes that the In this paper we report the results of a Mantel-Haenszel distribution of birthweight and gestational age among procedure, which was used to determine the relationship Indigenous babies reflects the prevalence of antenatal risk between perinatal mortality and Indigenous status factors such as smoking, infection, maternal nutrition and adjusted for the effect of low birthweight and preterm psycho-social stress; while any excess of mortality that birth. The proportion and number of deaths that could be remains after the excess low-birthweight and preterm risk avoided were estimated by comparison of the crude and among Indigenous babies is removed might say some- adjusted rates. thing about the quality of medical care at the time of confinement. We also used Poisson-regression models to adjust perina- tal mortality rates for birthweight and gestational age. We Although such reasoning has many proponents [11-13], variously fitted single week or four week categories of ges- risk factors such as smoking and infection are likely to also tational age and 250 g and 500 g categories of birth have at least a small effect on mortality that is independ- weight. The results were the same as using the Mantel- ent of birthweight and gestational age. That is, adjustment Haenzel approach with broad categories of gestational age of perinatal mortality rates by birthweight and gestational and birthweight, and we included these in preference to age is not a perfect way of assessing the quality of medical the Poisson-regression models for ease of interpretation. care at the time of confinement. It is similar to case-mix adjustments used in other settings to allow for differences Results in risk [14,15]. Such adjustments are not expected to The crude perinatal mortality rate among Indigenous remove all confounding. Instead, the reasoning is that the babies was 19.6 per 1000 births, which was 2.01 adjusted rates, although not perfect, provide a useful way (95%ci:1.77,2.28) times higher than the rate among non- Page 2 of 5 (page number not for citation purposes) Australia and New Zealand Health Policy 2005, 2:11 http://www.anzhealthpolicy.com/content/2/1/11 Perinatal mortality rate ratio Born prior to 28 weeks 1.02 (0.86-1.21) Born 28-36 weeks 1.24 (0.94-1.62) Born 37+ weeks, weight <2500g 0.94 (0.41-1.88) Born 37+ weeks, weight >2500g 1.55 (1.09-2.14) Crude overall RR 2.01 (1.77-2.28) Mantel-Haenszel combined RR 1.13 (0.99-1.28) Source: Queensland Perinatal Data Collection 2 Figure 1 Rate ratios 002 comparing Indigenous to non-Indigenous perinatal mortality stratified by preterm and birthweight status, 1998– Rate ratios comparing Indigenous to non-Indigenous perinatal mortality stratified by preterm and birthweight status, 1998– 2002. a) Rate ratios greater than 1.0 indicate higher mortality among Indigenous babies. b) Differences between stratum-spe- cific rate ratios are not statistically significant (χ (3) = 5.78, p = 0.1226). Indigenous babies. When perinatal mortality rates were is adequate for Indigenous mothers and babies. That is, compared within each birthweight and gestational age priority should initially be given to primary health care strata, the point estimates suggested that Indigenous interventions to reduce the proportion of preterm and low babies were only slightly more likely to die than non- birth weight babies. Indigenous babies (Figure 1). The test for homogeneity of the rate ratios across strata was not significant (χ (3) = Policy implications 5.78, p = 0.1226) suggesting that the effect of Indigenous Risk factors for preterm birth and low birth weight include status is the same across the birthweight and gestational smoking, gentio-urinary tract infections, poor maternal age strata (except for statistical noise) and that it is appro- nutrition and psycho-social stress [16-19]. Several studies priate to use the adjusted combined estimate: M-H have reported a higher prevalence of these risk factors Adjusted RR = 1.13, 0.99–1.28. among Indigenous compared with non-Indigenous mothers. These results suggest that if the population of Indigenous babies had the same birthweight and gestational age dis- More specifically, the prevalence of smoking among tribution as non-Indigenous babies, then the relative dis- Indigenous women during pregnancy has been reported parity would be reduced by 87% and there would be 20 to be more than 60%, which is at least 3 times the preva- fewer deaths of Indigenous babies per year. lence for non-Indigenous women [9,20,21]. A recent Cochran review found that there are effective primary Discussion health care interventions to help and support women to Interpretation of results stop smoking that lead to fewer preterm babies and better Perinatal mortality among Indigenous babies has birthweights [22]. Further, we know that Indigenous remained twice that of their non-Indigenous counterparts women are more than two times as likely to have a urinary for more than a decade. We found that most of this mor- tract infection during pregnancy as non-Indigenous tality excess is because Indigenous babies are at greater women [23]. In overseas studies, primary health care risk of being born too early and too small. In contrast, the interventions to detect and treat asymptomatic bacteruria case fatality rates of Indigenous babies who were born pre- have been shown to decrease preterm birth by 40% [24]. term or of low birth weight were similar to their non- Indigenous counterparts. In Australia, the best example we have of a primary health care initiative aimed at reducing risk factors among Indig- Using a framework advocated by several perinatal epide- enous mothers is the Strong Women Strong Babies Strong miologists [11-13], these results suggests that, broadly Culture program in the Northern Territory [25]. This pro- speaking, access to high quality care during confinement gram resulted in increased early attendance for antenatal Page 3 of 5 (page number not for citation purposes) Australia and New Zealand Health Policy 2005, 2:11 http://www.anzhealthpolicy.com/content/2/1/11 care, reduced numbers of STDs and a reduced proportion of the mortality excess for Indigenous people and pro- of low birthweight babies [26]. vides robust support for policy discussions. Although such results are encouraging, if substantial For several reasons, gestational age is known to be less progress is to be made across the whole of Australia, a accurate among Indigenous than non-Indigenous babies properly funded national initiative is needed. Such an ini- [31]. Nevertheless, previous work in Queensland and else- tiative would include funding to improve access to cultur- where has shown that gestational age in combination ally appropriate primary health care during the antenatal with birthweight provides a better statistical adjustment of period, which would deliver, inter alia, interventions for mortality rates than birthweight alone [32,33]. We there- smoking cessation, screening and treatment of genito-uri- fore considered it better to present birthweight and gesta- nary tract infections, screening for domestic violence, and tional age adjusted rates, rather than just birthweight- programs aimed at reducing alcohol consumption and adjusted rates. poor nutrition. Conclusion Although perinatal mortality rates in Queensland have It would not be a case of one strategy fits all. Instead local partnerships with possibly different types of service mod- decreased over the last 16 years, the rates in Indigenous els would be needed to implement the national initiative. populations remain at least double those in the non- This approach will encourage creativity, innovation and Indigenous population. Our analyses, stratified by birth- risk taking, which will be essential ingredients to tackling weight and gestational age, suggest that the priority for a situation that has proved difficult to improve. reducing the excess mortality among Indigenous babies is primary health care to reduce the prevalence of risk factors Study limitations during the antenatal period. A primary health care Using vital statistics to set agendas has a long and contin- approach encompasses a much-needed component of an uing tradition in public health [27]. The advantages of overall shift towards empowerment of Indigenous such statistics are convenience, low cost and total enumer- women and increased awareness and ownership of health ation. The disadvantages are insufficient and inaccurate which has the potential to play an important role in data, which create uncertainty about the validity of the reducing the social inequality that has resulted in out- results [27]. 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Australian College of Widwives Publish with Bio Med Central and every Journal 1995:26-29. scientist can read your work free of charge 29. Paradies Y, Cunningham J: Placing Aboriginal and Torres Strait Islander mortality in an international context. Australian and "BioMed Central will be the most significant development for New Zealand Journal of Public Health 2002, 26(1):11-16. disseminating the results of biomedical researc h in our lifetime." 30. Kaufman J: How inconsistencies in racial classification demys- Sir Paul Nurse, Cancer Research UK tify the race construct in public health statistics. Epidemiology 1999, 10:101-103. Your research papers will be: 31. Day P, Sullivan EA, Lancaster P: Indigenous mothers and their available free of charge to the entire biomedical community babies. In Perinatal Statistical Series No 8 Sydney , AIHW National Perinatal Statistics Unit; 1999. peer reviewed and published immediately upon acceptance 32. Coory M: Does gestational age in combination with birth- cited in PubMed and archived on PubMed Central weight provide a better statistical adjustment of neonatal mortality rates than birthweight alone? Paediatric Perinatal yours — you keep the copyright Epidemiology 1997, 11:385-391. BioMedcentral Submit your manuscript here: http://www.biomedcentral.com/info/publishing_adv.asp Page 5 of 5 (page number not for citation purposes)

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