IJE Advance Access published online on September 20, 2008
International Journal of Epidemiology, doi:10.1093/ije/dyn194
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
A comparison of foetal and infant mortality in the United States and Canada
1Division of Epidemiology and Biostatistics, Department of Obstetrics, Gynecology, and Reproductive Sciences, UMDNJ-Robert Wood Johnson Medical School, New Jersey, USA.
2Maternal and Infant Health Section, Health Surveillance and Epidemiology Division, Public Health Agency of Canada, Ottawa, Canada.
3Perinatal Epidemiology Research Unit, Departments of Obstetrics and Gynaecology, and Pediatrics, Dalhousie University and the IWK Health Centre, Halifax, Canada.
4Departments of Pediatrics and of Epidemiology and Biostatistics, McGill University, Montreal, Canada.
* Corresponding author: Division of Epidemiology and Biostatistics, Department of Obstetrics, Gynecology, and Reproductive Sciences, UMDNJ-Robert Wood Johnson Medical School, 125 Paterson Street, New Brunswick, NJ 08901-1977, USA. E-mail: cande.ananth{at}umdnj.edu
 |
Abstract |
|---|
 Top Abstract IntroductionMaterial and methodsResultsCommentFundingAcknowledgementsReferences |
|---|
Background Infant mortality rates are higher in the United States than in Canada. We explored this difference by comparing gestational age distributions and gestational age-specific mortality rates in the two countries.
Methods Stillbirth and infant mortality rates were compared for singleton births at 
22 weeks and newborns weighing 500 g in the United States and Canada (1996–2000). Since menstrual-based gestational age appears to misclassify gestational duration and overestimate both preterm and postterm birth rates, and because a clinical estimate of gestation is the only available measure of gestational age in Canada, all comparisons were based on the clinical estimate. Data for California were excluded because they lacked a clinical estimate. Gestational age-specific comparisons were based on the foetuses-at-risk approach.
Results The overall stillbirth rate in the United States (37.9 per 10 000 births) was similar to that in Canada (38.2 per 10 000 births), while the overall infant mortality rate was 23% (95% CI 19–26%) higher (50.8 vs 41.4 per 10 000 births, respectively). The gestational age distribution was left-shifted in the United States relative to Canada; consequently, preterm birth rates were 8.0 and 6.0%, respectively. Stillbirth and early neonatal mortality rates in the United States were lower at term gestation only. However, gestational age-specific late neonatal, post-neonatal and infant mortality rates were higher in the United States at virtually every gestation. The overall stillbirth rates (per 10 000 foetuses at risk) among Blacks and Whites in the United States, and in Canada were 59.6, 35.0 and 38.3, respectively, whereas the corresponding infant mortality rates were 85.6, 49.7 and 42.2, respectively.
Conclusions Differences in gestational age distributions and in gestational age-specific stillbirth and infant mortality in the United States and Canada underscore substantial differences in healthcare services, population health status and health policy between the two neighbouring countries.
Keywords Stillbirth, infant mortality, preterm delivery, clinical estimate of gestation, foetuses-at-risk, neonatal intensive care, Kitagawa analysis
Accepted 19 August 2008
|
Introduction |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentFundingAcknowledgementsReferences |
|---|
Adequate and timely provision of healthcare to mothers and newborns is the cornerstone for improving maternal and perinatal health outcomes. Advances in obstetrics and dramatic improvements in neonatal care have occurred in recent decades in most industrialized countries. Despite the higher spending on overall healthcare and on newborn intensive care in the United States,1 infant mortality rates in the United States is higher than in Canada. In 2003, for instance, the infant mortality rate in the United States was 6.9 per 1000 live births compared with 5.3 per 1000 live births in Canada.2 This contrast between neighbouring countries is of interest for a variety of reasons. These include (i) the geographic proximity and the frequent contact between clinicians between the two countries; (ii) the fact that both countries recognize and accept training in the other for licensing purposes are compelling reasons to explore differences in stillbirth and infant mortality between the United States and Canada; and (iii) differences in healthcare systems; in contrast to healthcare in the United States, the Canadian healthcare system is publicly funded and hospital care is mostly administered through not-for-profit institutions.
This disparity in infant mortality rates could be a consequence of differences in gestational age distributions or in gestational age-specific mortality. In general, differences in gestational age distributions reflect aspects of maternal health, whereas differences in gestational age-specific mortality reflect differences in healthcare, both obstetric and neonatal. Other factors, which could provide some insights into international differences in infant mortality, include age at death (including rates of stillbirth, early neonatal, late neonatal and post-neonatal death) and causes of death. Thus, higher stillbirth rates at term can reflect lesser access to, or use or quality of, foetal monitoring and obstetric interventions, while higher post-neonatal mortality rates can be a consequence of adverse health behaviours (prone sleep position, unintentional injury.)
We carried out a population-based study to compare gestational age distributions, gestational age-specific mortality, age at death and causes of death in order to explore the reasons for persistent differences in infant mortality between the United States and Canada.
|
Material and methods |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentFundingAcknowledgementsReferences |
|---|
United States birth cohort composition
We used the United States natality and foetal death data files, 1996 through 2000, assembled by the National Center for Health Statistics of the Centers for Disease Control and Prevention. The data included all live births and foetal deaths, as well as live births linked to their corresponding infant deaths to women who delivered within the 50 contiguous states and the District of Columbia. Data from each state were transferred to the National Center for Health Statistics on an annual basis under the vital statistics registration programme.3
Two measures of gestational age are currently available in the data files: a menstrual estimate and a clinical estimate.3 The exact source of the clinical estimate of gestational age is not documented, however, i.e. whether it is based on an ultrasound, obstetrical or newborn examination estimate. Two reasons favoured our choice of the clinical estimate over the menstrual-based estimate. First, gestational age based on menstrual dates appears to misclassify gestational duration4 and overestimate both preterm and postterm birth rates.2 Second, the only measure of gestational age available in the Canadian data was the clinical estimate. Therefore, our analyses comparing gestational age-specific mortality between the United States and Canada were based on the clinical estimate of gestation.
Canadian birth cohort composition
Data on Canadian stillbirths were obtained from Statistics Canada's stillbirth database for the years 1996 through 2000, while data on live births and infant deaths were obtained from the linked live births–infant deaths file for the same years.5 As mentioned above, a single (best) estimate of gestational age is available in these databases and corresponds to the clinical estimate of gestational age in the United States files.2 Previous research suggests that gestational age information in the database is reliable.6
Data exclusions for United States births
Data were abstracted for singleton live births, stillbirths and infant deaths between 1996 and 2000. We sequentially excluded the following categories of singleton births from the data files: births from the state of California (n = 2 584 483), missing birthweight (n = 121 321), birthweight below 500 g (n = 83 101), missing clinical estimate of gestational age (n = 162 889) and clinical estimate of gestational age <22 completed weeks (n = 71 380). Foetuses with birthweight below 500 g were excluded to minimize possible bias due to variations in registration practices of births especially at the borderline of viability.7,8 Exclusion of births from the state of California was necessary because the clinical estimate of gestational age was not reported by this state.4 Following all exclusions, 16 568 581 singleton live births and stillbirths remained for analysis.
Data exclusions for Canadian births
Births to mothers residing in Ontario (n = 793 806) were excluded because of documented problems with data quality,9 including large numbers of unlinked infant deaths. Singleton foetuses with missing gestational age (n = 2587), gestational age <22 completed weeks (n = 1635), missing birthweight (n = 2769), or birthweight below 500 g (n = 2106) were sequentially excluded. After all exclusions, 1 257 187 singleton live births and stillbirths remained for analysis.
Statistical analysis
We first compared the distribution of birthweight and gestational age between the United States and Canadian live births, as well as rates of low birthweight (<2500 g) and preterm birth (<37, <34 and <32 weeks) between the two countries. This analysis was followed by a comparison of mortality rates between the United States and Canada and included the following: stillbirth (at 22 weeks or greater), early neonatal (deaths that occurred within the first 6 days after birth), late neonatal (deaths that occurred between 7 and 27 days), post-neonatal (deaths that occurred between 28–364 days) and infant (deaths that occurred within the first year after birth) mortality. We computed a rate ratio (RR) with 95% confidence interval (95% CI) for each mortality index in the United States vs Canada (reference).
These overall contrasts between the two countries were followed by a comparison of gestational age-specific mortality rates, based on the foetuses-at-risk approach.10–12 Under the foetuses-at-risk approach, the gestational age-specific rate of stillbirth, for instance, is calculated by dividing the number of stillbirths at a given gestational week by the total number of foetuses at risk of stillbirth at that gestation (i.e. all foetuses that are stillborn or delivered alive at that or a later gestation). This model provides better description of gestational age-specific mortality rates, since the entire population at ‘risk’ is included in the denominator. Furthermore, the model eliminates paradoxical crossovers in gestational age-specific mortality that is typically seen in comparisons by plurality, parity, race, etc.
Finally, we estimated the independent contributions of differences in gestational age distributions vs differences in gestational age-specific infant mortality between the United States and Canada. This was accomplished by a modified Kitagawa decomposition method.13,14 In the original Kitagawa decomposition, the two components are the gestational age distribution multiplied by the gestational age-specific mortality rate. We adapted a modified Kitagawa decomposition method by multiplying the fraction of the cohort (of foetuses) at risk at the beginning of any gestational week by the corresponding gestational age-specific mortality rate. This analysis was limited to early and late neonatal deaths, since births and deaths comprise the same event for stillbirths.
All statistical analyses were carried out using SAS (version 9.1; SAS Institute, Cary, NC).
Causes of death coding
Based on the foetuses-at-risk approach, we also contrasted gestational age-specific cause of death between the United States and Canada. This analysis was restricted to infant deaths only, since the causes of death data for stillbirths in the United States were unavailable. Causes of death were classified based on the International Classification of Diseases (ICD) versions 9 for 1996 through 1998 for the United States and 1996 through 2000 for the Canadian data, and ICD-10 for 1999 and 2000 for the United States data. Causes of death were grouped using the modified International Collaborative Effort (ICE) classification15 as follows: congenital anomalies (ICD-9-CM 740.0 to 759.8 and ICD-10 Q00 to Q99); maternal complications including complications of the placenta, umbilical cord and the chorio-amniotic membranes (ICD-9-CM 761.0 to 762.9 and ICD-10 P00 to P04.9); short gestation, low birthweight or slow foetal growth (ICD-9-CM 764.0 to 766.0 and ICD-10 P05 to P08.2); intrauterine hypoxia, birth asphyxia or respiratory distress syndrome (ICD-9-CM 768.0 to 769.0 and ICD-10 P20 to P29.9); infections arising in the perinatal period (ICD-9-CM 771.0 to 772.0 and ICD-10 P35 to P39.9); sudden infant death syndrome (ICD-9-CM 798.0 and ICD-10 R95); and injury-related deaths (ICD-9-CM E800-E869 and E880-E929 and ICD-10 V01-X59). Injury-related deaths exclude those with accidents following medical or surgical procedures and complications.
To explore the role of racial disparities in explaining the observed inter-country differences, we also compared overall and gestational age-specific mortality among births to White and Black women in the United States and all births in Canada.
|
Results |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentFundingAcknowledgementsReferences |
|---|
The distribution of maternal characteristics for births in the United States and Canada are contrasted in Table 1. Maternal age distributions showed a higher frequency of teenage births in the United States and a higher proportion of mothers 30 years or older in Canada. Proportions of low birthweight (below 2500 g) and very low birthweight (below 1500 g), as well as preterm birth (below 37 weeks, and below 32 weeks) were higher in the United States than in Canada (Table 2). There was a left-shift in both the birthweight and gestational age distributions in the United States relative to Canada (Figure 1).
|
|
|
The overall stillbirth rate was similar (RR 0.99, 95% CI: 0.95, 1.04) between the United States than Canada (Table 3). While overall early neonatal mortality rates were also similar between the two countries, rates of late neonatal, post-neonatal and infant mortality were higher in the United States.
|
Gestational age-specific rates of stillbirth and early neonatal mortality between United States and Canada are contrasted in Figure 2. Stillbirth rates at term gestation (at 37 weeks and beyond) were lower in the United States; at preterm gestations, stillbirth rates were similar between the two countries. Overall early neonatal mortality rates were similar between United States and Canada (19.8 vs 19.4 per 10 000 births, respectively), but gestational age-specific early neonatal mortality rates at at term gestations and at 29–32 weeks were lower in the United States than in Canada, albeit similar at other preterm gestational ages. Contrasts of late neonatal and post-neonatal mortality rates between the two countries revealed higher rates in the United States at every gestational week (Figure 3).
|
|
Results of the analysis based on the modified Kitagawa decomposition method are shown in Table 4 and quantify the contribution of between country differences in the gestational age distribution and gestational age-specific mortality to differences in early and late neonatal mortality. This analysis indicates that differences in early and late neonatal mortality rates between the two countries (0.348 and 2.523 per 10 000 births, respectively) were mainly due to differences in the gestational age-specific mortality. In addition, these differences in mortality rates contributed more at preterm than at term gestations. Specifically, for early neonatal death rate differences, the between-country differences in gestational age distribution at term favoured the United States, whereas gestational age-specific mortality rates substantially favoured Canada at preterm gestations and the United States to a lesser extent at term gestations. With regard to late neonatal deaths, the gestational age distribution at term favoured the United States, whereas the gestational age-specific mortality rates overwhelmingly favoured Canada at both preterm and term gestations. Note the differences in the gestational age distribution at term (Figure 1): the gestational age distribution at term in the United States was left-shifted relative to Canada, possibly indicating higher levels of foetal surveillance and obstetric intervention at term gestation in the United States.
|
Causes of infant death between births in the United States and Canada are contrasted Table 5. Infant deaths due to virtually every cause (with the exception of maternal complications at term) were higher in the United States than Canada.
|
Analyses carried out after stratifying the United States data by maternal race showed that the overall stillbirth rates (per 10 000 total births) among Blacks and Whites were 59.6 and 35.0, respectively, in comparison to a rate of 38.3 per 10 000 total births in Canada. Gestational age-specific stillbirth rates showed that the rate among Blacks in the United States was consistently higher at every gestation week with the rates among United States Whites and those of Canadian births fairly similar. In contrast, rates of infant mortality among Blacks and Whites in the United States and in Canada were 85.6, 49.7 and 42.2, respectively. Infant mortality rates were higher at every gestation week among United States Blacks and similar at early (22–27 weeks) and late gestation (at and beyond 41 weeks) between United States Whites and Canadian births; between 28 and 40 weeks, infant mortality rates were higher at virtually every gestation in United States Whites than in Canada.
|
Comment |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentFundingAcknowledgementsReferences |
|---|
Our study shows that the distribution of gestational age based on the clinical estimate was left shifted in the United States, as was birthweight, leading to higher rates of preterm birth and low birthweight, respectively, in the United States than in Canada. Stillbirth and early neonatal mortality rates at term were lower in the United States than in Canada (and at 29–32 weeks for the early neonatal death), while late neonatal and post-neonatal mortality rates were consistently higher in the United States at every gestational week.
Arguably, differences in socio-demographic (race/ethnic composition, maternal age, parity) and behavioural factors (maternal smoking, alcohol and drug use and pre-pregnancy body-mass) between the United States16 and Canada17 may account for much of the differences in the observed mortality between the two countries. In addition, within the United States, the substantial differences in mortality may be secondary to differences in socio-demographic and behavioural factors between Blacks and Whites. We were unable to carry out inter-country comparisons based on maternal race, since ascertainment of race is not permitted on Canadian birth registrations. However, Canadian Blacks constituted 2.2% of the Canadian population according to the 2001 census.18 Issues of race-based disparities in healthcare within Canada tend to focus on poorer healthcare services and health status among Canada's First Nations (American Indian), Inuit and Metis populations which constitute about 3.8% of the Canadian population. Differences in patterns of health care delivery19 including variations in provision of care by neonatologists, volume of intensive care units, and regionalization of obstetric services20–22 may have likely affected global comparisons of gestational age-specific perinatal and infant mortality between the two countries.
Despite the benefits of aggressive neonatal interventions and liberal use of surfactant and antenatal glucocorticoids in improving the survival of extremely preterm infants,23–25 attitudes to setting limits to neonatal intensive care for newborns delivered at very preterm gestations (i.e. 20–23 weeks) or extremely ill newborns show large variations both between individual physicians and across countries.26,27 It is plausible that such physician opinions and attitudes about providing neonatal intensive care to sick newborns may have partly contributed to some of the observed differences in stillbirth and neonatal mortality rates between the United States and Canada. More widespread use of foetal monitoring and indicated early delivery in the United States than Canada may have also helped prevent stillbirths at term. However, lack of data on labour induction and pre-labour caesarean delivery in the Canadian birth registration database used in this study precluded us from exploring this further.
If the higher spending for neonatal intensive care system in the United States is indeed beneficial, then the benefit is largely confined to preventing early neonatal deaths at term. Aggressive intervention early in gestation in the United States relative to that in Canada may have in fact resulted in delaying early neonatal deaths to the late neonatal or even the post-neonatal period. This is particularly appealing in light of the Kitagawa analysis that showed that differences in neonatal mortality rates between the two countries are more pronounced at preterm than at term gestations (Table 4). This difference in intervention may explain, at least in part, the lower early neonatal mortality at 29–32 weeks in the United States. In addition, these differences may be a result of poor data quality, since misclassification of term births as preterm due to transcription errors are likely to affect this gestational age range disproportionately (entry of a ‘2’ instead of a ‘3’ can result in a recorded gestational of age of 28 or 29 weeks instead of 38 or 39 weeks; a ‘3’ instead of a ‘4’ will result in 30, 31 or 32 weeks instead of 40, 41 or 42 weeks). The observation that late neonatal and post-neonatal mortality rates, both overall and gestational age-specific, are higher in the United States suggests that the benefits of more aggressive care are confined to a small ‘risk period’ (early neonatal deaths relative to all infant deaths). The higher post-neonatal mortality in the United States suggests more frequent adverse health behaviours, such as prone sleeping (a widely recognized risk factor for the sudden infant death syndrome) and unintentional injury, at least within at-risk subpopulations. Arguably, these differences may reflect pockets with a high prevalence of economic and social disadvantage in the United States.
The major international mortality differences ‘favouring’ the United States are marginally lower stillbirth rates and lower early neonatal mortality rates at term gestation. These lower rates probably reflect more intensive obstetric monitoring and early delivery (i.e. labour induction and/or caesarean delivery) as regards stillbirths and more aggressive neonatal intensive care as regards early neonatal mortality. The former probably reflects a real improvement and is likely due to differences in access or quality of care. The latter may reflect differences in neonatal intensive care, but may also reflect differences in legal, cultural or religious attitudes (e.g. ‘save lives at all costs’ phenomenon or the ‘Baby Doe’ effect) between the two countries.28
Limitations and strengths
A few limitations and strengths of our international comparison merit some discussion. Registration differences between the two countries may have been responsible for some of the observed differences in mortality. While the menstrual estimate of gestational age is prone to several kinds of errors,29,30 the clinical estimate is based on the clinician's ‘best’ estimate of gestational age, and therefore, less likely to be effected by such errors. This is evident from the absence of a bimodal distribution in the clinical estimate at preterm gestational ages.4 Restricting our mortality comparisons to foetuses that weighed at least 500 g avoids some of the artefacts due to variations in the registration of births at the borderline of viability.7 Finally, the possibility of potential transcription errors and incorrect coding of causes of death in both the United States and Canada cannot be overlooked.
The conceptual analytic approach in our international gestational age-specific mortality comparisons reflects an obstetrical model that is based on ongoing pregnancies/foetuses at risk.31 Studies have shown this model to be more appropriate for end-points that occur on a continuum of gestational age.12,32,33
Conclusions
Our study shows that compared with Canada, the United States has much higher rates of preterm birth and low birthweight, lower rates of stillbirth at term, similar overall rates of early neonatal death and substantially higher rates of late neonatal mortality, post-neonatal mortality and infant mortality. These differences appear to be secondary to differences in the social determinants of health as well as public health emphasis—lower rates of preterm birth and low birthweight in Canada suggest better maternal health status and differences in infant mortality rates suggest better infant care in the post-neonatal period in Canada. On the other hand, hospital care to prevent stillbirths and early neonatal death at term gestation appears to be better in the United States; the relatively high rates of such deaths in Canada are surprising given the relatively low rates of preterm birth and low birthweight. Regardless, both countries may stand to benefit from a cautious re-examination of health services needs and an identification of public health priorities that could benefit from additional resources.
|
Funding |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentFundingAcknowledgementsReferences |
|---|
Canadian Institutes of Health Research Peter Lougheed New Investigator award (to K.S.J.).
|
Acknowledgements |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentFundingAcknowledgementsReferences |
|---|
We thank Ms Joyce Martin (National Center for Health Statistics of the United States Centers for Disease Control and Prevention) for clarifications regarding the reporting of foetal deaths and live births in the United States.
Conflict of interest: None declared.
Key Messages
|
|
References |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentFundingAcknowledgementsReferences |
|---|
1 Thompson LA, Goodman DC, Little GA. Is more neonatal intensive care always better? Insights from a cross-national comparison of reproductive care. Pediatrics (2002) 109:1036–43.
2 Joseph KS, Huang L, Liu S, et al. Reconciling the high rates of preterm and postterm birth in the United States. Obstet Gynecol (2007) 109:813–22.[CrossRef][Web of Science][Medline]
3 Taffel SM, Ventura SJ, Gay GA. Revised U.S. certificate of birth–new opportunities for research on birth outcome. Birth (1989) 16:188–93.[Web of Science][Medline]
4 Ananth CV. Menstrual versus clinical estimate of gestational age dating in the United States: temporal trends and variability in indices of perinatal outcomes. Paediatr Perinat Epidemiol (2007) 21(Suppl 2):22–30.[Medline]
5 Fair M, Cyr M, Allen AC, Wen SW, Guyon G, MacDonald RC. An assessment of the validity of a computer system for probabilistic record linkage of birth and infant death records in Canada. The Fetal and Infant Health Study Group. Chronic Dis Can (2000) 21:8–13.[Medline]
6 Kramer MS, Demissie K, Yang H, Platt RW, Sauve R, Liston R. The contribution of mild and moderate preterm birth to infant mortality. Fetal and Infant Health Study Group of the Canadian Perinatal Surveillance System. JAMA (2000) 284:843–49.
7 Joseph KS, Kramer MS. Recent trends in Canadian infant mortality rates: effect of changes in registration of live newborns weighing less than 500 g. CMAJ (1996) 155:1047–52.[Abstract]
8 Kramer MS, Platt RW, Yang H, Haglund B, Cnattingius S, Bergsjo P. Registration artifacts in international comparisons of infant mortality. Paediatr Perinat Epidemiol (2002) 16:16–22.[Web of Science][Medline]
9 Births. (2003) Ottawa, Canada: Statistics Canada. 2005.
10 Joseph KS. Theory of obstetrics: an epidemiologic framework for justifying medically indicated early delivery. BMC Pregnancy Childbirth (2007) 7:4.[CrossRef][Medline]
11 Joseph KS. Theory of obstetrics: the fetuses-at-risk approach as a causal paradigm. J Obstet Gynaecol Can (2004) 26:953–60.[Medline]
12 Yudkin PL, Wood L, Redman CW. Risk of unexplained stillbirth at different gestational ages. Lancet (1987) 1:1192–94.[Web of Science][Medline]
13 Kitagawa E. Components of a difference between two rates. J Am Statist Assoc (1956) 50:1169–94.
14 Berman SM. Movable partitions: methodological problems in assessing improvement in neonatal mortality. Am J Epidemiol (1985) 122:354–55.
15 Cole S, Hartford RB, Bergsjo P, McCarthy B. International collaborative effort (ICE) on birth weight, plurality, perinatal, and infant mortality. III: a method of grouping underlying causes of infant death to aid international comparisons. Acta Obstet Gynecol Scand (1989) 68:113–17.[Web of Science][Medline]
16 Singh GK, Kogan MD. Persistent socioeconomic disparities in infant, neonatal, and postneonatal mortality rates in the United States, 1969–2001. Pediatrics (2007) 119:e928–39.
17 Kramer MS, Goulet L, Lydon J, et al. Socio-economic disparities in preterm birth: causal pathways and mechanisms. Paediatr Perinat Epidemiol (2001) 15(Suppl 2):104–23.[CrossRef][Web of Science][Medline]
18 Milan A, Tran K. Blacks in Canada: A Long History. Canadian social trends. (2004) Statistics Canada. (Catalogue No 11-008).
19 Yeast JD, Poskin M, Stockbauer JW, Shaffer S. Changing patterns in regionalization of perinatal care and the impact on neonatal mortality. Am J Obstet Gynecol (1998) 178(Pt 1):131–15.[CrossRef][Web of Science][Medline]
20 Bird ST, Bauman KE. The relationship between structural and health services variables and state-level infant mortality in the United States. Am J Public Health (1995) 85:26–29.
21 Crosse EA, Alder RJ, Ostbye T, Campbell MK. Small area variation in low birthweight: looking beyond socioeconomic predictors. Can J Pub Health (1997) 88:57–61.[Web of Science][Medline]
22 Phibbs CS, Bronstein JM, Buxton E, Phibbs RH. The effects of patient volume and level of care at the hospital of birth on neonatal mortality. JAMA (1996) 276:1054–59.
23 Allen MC, Donohue PK, Dusman AE. The limit of viability—neonatal outcome of infants born at 22 to 25 weeks' gestation. N Engl J Med (1993) 329:1597–601.
24 Soll RF, McQueen MC. Respiratory distress syndrome. In: Effective Care of the Newborn Infant—Sinclair JC, Bracken MB, eds. (1992) Oxford: Oxford University Press. 235–358.
25 Stevens TP, Blennow M, Soll RF. Early surfactant administration with brief ventilation vs selective surfactant and continued mechanical ventilation for preterm infants with or at risk for RDS. Cochrane Database Syst Rev (2002) CD003063.
26 De Leeuw R, Cuttini M, Nadai M, et al. Treatment choices for extremely preterm infants: an international perspective. J Pediatr (2000) 137:608–16.[CrossRef][Web of Science][Medline]
27 Rebagliato M, Cuttini M, Broggin L, et al. Neonatal end-of-life decision making: physicians' attitudes and relationship with self-reported practices in 10 European countries. JAMA (2000) 284:2451–59.
28 Paris JJ, Schreiber MD, Moreland MP. Parental refusal of medical treatment for a newborn. Theor Med Bioeth (2007) 28:427–41.[CrossRef][Web of Science][Medline]
29 Kramer MS, McLean FH, Boyd ME, Usher RH. The validity of gestational age estimation by menstrual dating in term, preterm, and postterm gestations. JAMA (1988) 260:3306–08.
30 Savitz DA, Terry JW Jr, Dole N, Thorp JM Jr, Siega-Riz AM, Herring AH. Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination. Am J Obstet Gynecol (2002) 187:1660–66.[CrossRef][Web of Science][Medline]
31 Joseph KS. Incidence-based measures of birth, growth restriction, and death can free perinatal epidemiology from erroneous concepts of risk. J Clin Epidemiol (2004) 57:889–97.[CrossRef][Web of Science][Medline]
32 Joseph K, Liu S, Demissie K, et al. A parsimonious explanation for intersecting perinatal mortality curves: understanding the effect of plurality and of parity. BMC Pregnancy Childbirth (2003) 3:3.[CrossRef][Medline]
33 Joseph KS, Demissie K, Platt RW, Ananth CV, McCarthy BJ, Kramer MS. A parsimonious explanation for intersecting perinatal mortality curves: understanding the effects of race and of maternal smoking. BMC Pregnancy Childbirth (2004) 4:7.[CrossRef][Medline]
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||