Perinatal health among foreign versus native-born mothers in Canada: variations across outcomes and cohorts.

BACKGROUND: To examine perinatal health differences between foreign-born and native-born mothers in Canada across multiple outcomes and two cohorts 10 years apart. METHODS: Using 94 896 and 131 271 births in the 1996 and 2006 Canadian Census-Birth Cohort, respectively, we estimated risk ratios and risk differences of preterm birth (PTB), small-for-gestational age (SGA), large-for-gestational age (LGA), stillbirth and infant mortality between foreign-born and Canadian-born mothers. RESULTS: In the 1996 cohort, we observed no important differences in adverse outcomes between foreign-born and native-born mothers. In the 2006 cohort, however, foreign-born mothers had lower risks of PTB, LGA, stillbirth, and infant mortality and a higher risk of SGA on both the relative and absolute scales. Lowered risk of PTB among foreign-born mothers in the 2006 cohort was also observed within Caucasian, East Asian, Southeast Asian and South Asian mothers. Favourable outcomes associated with foreign-born status in the 2006 cohort were negatively graded by duration of residence in Canada among immigrant mothers. CONCLUSIONS: Differences in perinatal health by maternal foreign-born status varied across cohorts and a more pronounced 'healthy migrant' effect was observed among more recent migrants. The native-born mothers' perinatal health over time and a more restrictive/selective immigration policy in recent years would explain our results.

Positional accuracy of geocoding from residential postal codes versus full street addresses.

BACKGROUND: Postal codes are often the only geographic identifier available for assigning contextual or environmental information to a study population. This analysis assesses the influence of three factors-delivery mode type (mode of postal delivery), representative point type (source of latitude-longitude coordinates), and community size-on the accuracy of postal code spatial assignment. DATA AND METHODS: PCCF+ (Postal Code Conversion File Plus) was used to assign delivery mode type, representative point type and community size to each individual in the 2011 Census of Canada. A sample (n = 1,004) was randomly selected with a minimum of 90 observations for each category of those three factors. Based on the address information of individuals in the sample, measures of positional accuracy for geocoding from residential postal codes (PCCF+) versus reference locations as determined by full street addresses (Google Maps) were calculated using a geographic information system. Accuracy was measured as the distance that the geocoded position differed from the full street address. RESULTS: Positional accuracy was related primarily to mode of postal delivery. Rural and mixed (partly urban, partly rural) modes had much higher geocoding error than did urban modes. Rural and small-town Canada and latitude and longitude based on dissemination area centroids had low accuracy, largely because of their close relationship to rural and mixed modes of delivery. DISCUSSION: The accuracy of geocoding from postal codes can vary. Geocoding imprecision may result in misclassification, depending on the spatial resolution of the environmental or contextual measures. The spatial resolution required for a study helps to identify subpopulations that should be excluded because of inadequate positional accuracy.

Socioeconomic disparities in small-for-gestational-age birth and preterm birth.

BACKGROUND: Maternal socioeconomic disadvantage has been associated with increased risk of small-for-gestational-age birth and preterm birth. Few studies, however, have considered maternal education and income simultaneously to better understand the mechanisms underlying perinatal health disparities. This analysis examines both maternal education and income and their association with the risk of small-for-gestational-age birth and preterm birth. DATA AND METHODS: The study is based on 127,694 singleton live births from the 2006 Canadian Birth-Census Cohort, a national cohort of births registered from May 2004 to May 2006 that were linked to the 2006 long-form Census. Unadjusted rates of small-for-gestational-age birth (sex-specific birth weight below the 10th percentile for gestational age) and preterm birth (before 37 completed weeks of gestation) were estimated across selected maternal characteristics. Logistic regression was used to estimate crude and covariate-adjusted risk ratios of both outcomes according to maternal education and income adequacy quintiles. RESULTS: Small-for-gestational-age birth was associated with both maternal education and income adequacy, while preterm birth was associated with maternal education only. These findings persisted after taking factors including maternal age, ethnicity, and marital status into account. The results suggest that the mechanism by which maternal education is associated with these outcomes is likely not through income, nor does income replace education as a potentially meaningful measure of socioeconomic position. INTERPRETATION: The mechanisms underlying associations between socioeconomic position and perinatal health disparities are complex. The results of this study indicate that more than one socioeconomic factor may play a role.

Birth outcomes among First Nations, Inuit and Métis populations.

BACKGROUND: First Nations, Inuit, and Métis are at higher risk of adverse birth outcomes than are non-Indigenous people. However, relatively little perinatal information is available at the national level for Indigenous people overall or for specific identity groups. DATA AND METHODS: This analysis describes and compares rates of preterm birth, small-for-gestational-age birth, large-for-gestational-age birth, stillbirth, and infant mortality (neonatal, postneonatal, and cause-specific) in a nationally representative sample of First Nations, Inuit, Métis, and non-Indigenous births. The study cohort consisted of 17,547 births to Indigenous mothers and 112,112 births to non-Indigenous mothers from 2004 through 2006. The cohort was created by linking the Canadian Live Birth, Infant Death and Stillbirth Database to the long form of the 2006 Census, which contains a self-reported Indigenous identifier. RESULTS: With the exception of small-for-gestational-age birth, adverse birth outcomes occurred more frequently among First Nations, Inuit, and Métis women than among non-Indigenous women. Inuit had the highest preterm birth rate (11.4 per 100 births; 95% CI: 9.7 to 13.1) among the three Indigenous groups. The large-for-gestational-age rate was highest for First Nations births (20.9 per 100 births; 95% CI: 19.9 to 21.8). Infant mortality rates were more than twice as high for each Indigenous group compared with the non-Indigenous population, and rates of sudden infant death syndrome were more than seven times higher among First Nations and Inuit. DISCUSSION: The results confirm disparities in birth outcomes between Indigenous and non-Indigenous populations, and demonstrate differences among First Nations, Métis and Inuit.

The 2006 Canadian Birth-Census Cohort.

BACKGROUND: Evidence on socioeconomic and ethnocultural disparities in perinatal health in Canada tends to be limited to analyses by neighbourhood or for selected provinces. In 2010, the Canadian Institutes of Health Research awarded funding for a project on perinatal outcomes. This article describes the resulting 2006 Canadian Birth-Census Cohort Database. DATA AND METHODS: From the Canadian Live Birth, Infant Death and Stillbirth Database, 687,340 records of children born in Canada from May 16, 2004 through May 15, 2006 to mothers whose usual place of residence was Canada were selected as in-scope births. Deterministic rules were applied to link each person on the birth record-child, mother, father-to 2006 Census data.The cohort was restricted to records linked to a long-form questionnaire, and a cohort weight was developed. Cohort rates (unweighted and weighted) for five birth outcomes-preterm birth, small-for-gestational age, large-for-gestational age, stillbirth, and infant mortality-were compared with rates for all in-scope births across birth characteristics. Cohort rates for these birth outcomes were examined across selected census characteristics. RESULTS: Linkage rates were 91% for births surviving to age 1, 76% for stillbirths, and 80% for infant deaths matched to a birth registration. The cohort estimates were similar to those for all in-scope births, particularly after the cohort weight was applied. The cohort data produced plausible estimates of selected birth outcomes across maternal ethnocultural categories and levels of education. INTERPRETATION: The 2006 Canadian Birth-Census Cohort data can help inform perinatal surveillance and research in Canada.

Mortality following unemployment in Canada, 1991-2001.

BACKGROUND: This study describes the association between unemployment and cause-specific mortality for a cohort of working-age Canadians. METHODS: We conducted a cohort study over an 11-year period among a broadly representative 15% sample of the non-institutionalized population of Canada aged 30-69 at cohort inception in 1991 (888,000 men and 711,600 women who were occupationally active). We used cox proportional hazard models, for six cause of death categories, two consecutive multi-year periods and four age groups, to estimate mortality hazard ratios comparing unemployed to employed men and women. RESULTS: For persons unemployed at cohort inception, the age-adjusted hazard ratio for all-cause mortality was 1.37 for men (95% confidence interval (CI): 1.32-1.41) and 1.27 for women (95% CI: 1.20-1.35). The age-adjusted hazard ratio for unemployed men and women was elevated for all six causes of death: malignant neoplasms, circulatory diseases, respiratory diseases, alcohol-related diseases, accidents and violence, and all other causes. For unemployed men and women, hazard ratios for all-cause mortality were equivalently elevated in 1991-1996 and 1997-2001. For both men and women, the mortality hazard ratio associated with unemployment attenuated with age. CONCLUSIONS: Consistent with results reported from other long-duration cohort studies, unemployed men and women in this cohort had an elevated risk of mortality for accidents and violence, as well as for chronic diseases. The persistence of elevated mortality risks over two consecutive multi-year periods suggests that exposure to unemployment in 1991 may have marked persons at risk of cumulative socioeconomic hardship.

Cause-specific mortality by income adequacy in Canada: A 16-year follow-up study.

BACKGROUND: People with lower incomes tend to have less favourable health outcomes than do people with higher incomes. Because death registrations in Canada do not contain information about the income of the deceased, vital statistics cannot be used to examine mortality by income at the individual level. However, through record linkage, information on the individual or family income of people followed for mortality can be obtained. Recently, a large, population-based sample of Canadian adults was linked to almost 16 years of mortality data. METHODS: This study examines cause-specific mortality rates by income adequacy among Canadian adults. It is based on data from the 1991 to 2006 Canadian census mortality and cancer follow-up study, which followed 2.7 million people aged 25 or older at baseline, 426,979 of whom died during the 16-year period. Age-standardized mortality rates (ASMRs), rate ratios, rate differences and excess mortality were calculated by income adequacy quintile for various causes of death. RESULTS: For most causes examined, ASMRs were clearly graded by income: highest among people in the in the lowest income quintile, and lowest among people in the highest income quintile. Inter-quintile rate ratios (quintile 1/quintile 5) were greater than 2.00 for HIV/AIDS, diabetes mellitus, suicide, cancer of the cervix, and causes of death closely associated with smoking and alcohol. INTERPRETATION: These individually based results provide cause-specific information by income adequacy quintile that was not previously available for Canada.

Association of macrosomia with perinatal and postneonatal mortality among First Nations people in Quebec.

BACKGROUND: High prevalence of infant macrosomia (up to 36%, the highest in the world) has been reported in some First Nations communities in the Canadian province of Quebec and the eastern area of the province of Ontario. We aimed to assess whether infant macrosomia was associated with elevated risks of perinatal and postneonatal mortality among First Nations people in Quebec. METHODS: We calculated risk ratios (RRs) of perinatal and postneonatal mortality by birthweight for gestational age, comparing births to First Nations women (n = 5193) versus women whose mother tongue is French (n = 653 424, the majority reference group) in Quebec 1991-2000. RESULTS: The prevalence of infant macrosomia (birthweight for gestational age > 90th percentile) was 27.5% among births to First Nations women, which was 3.3 times (confidence interval [CI] 3.2-3.5) higher than the prevalence (8.3%) among births to women whose mother tongue is French. Risk ratios for perinatal mortality among births to First Nations women were 1.8 (95% CI 1.3-2.5) for births with weight appropriate for gestational age, 4.1 (95% CI 2.4-7.0) for small-for-gestational-age (< 10th percentile) births and < 1 (not significant) for macrosomic births compared to births among women whose mother tongue is French. The RRs for postneonatal mortality were 4.3 (95% CI 2.7-6.7) for infants with appropriate-for-gestational-age birthweight and 8.3 (95% CI 4.0-17.0) for infants with macrosomia. INTERPRETATION: Macrosomia was associated with a generally protective effect against perinatal death, but substantially greater risks of postneonatal death among births to First Nations women in Quebec versus women whose mother tongue is French.

Birth outcomes in the Inuit-inhabited areas of Canada.

BACKGROUND: Information on health disparities between Aboriginal and non-Aboriginal populations is essential for developing public health programs aimed at reducing such disparities. The lack of data on disparities in birth outcomes between Inuit and non-Inuit populations in Canada prompted us to compare birth outcomes in Inuit-inhabited areas with those in the rest of the country and in other rural and northern areas of Canada. METHODS: We conducted a cohort study of all births in Canada during 1990-2000 using linked vital data. We identified 13,642 births to residents of Inuit-inhabited areas and 4,054,489 births to residents of all other areas. The primary outcome measures were preterm birth, stillbirth and infant death. RESULTS: Compared with the rest of Canada, Inuit-inhabited areas had substantially higher rates of preterm birth (risk ratio [RR] 1.45, 95% confidence interval [CI] 1.38-1.52), stillbirth (RR 1.68, 95% CI 1.38-2.04) and infant death (RR 3.61, 95% CI 3.17-4.12). The risk ratios and absolute differences in risk for these outcomes changed little over time. Excess mortality was observed for all major causes of infant death, including congenital anomalies (RR 1.64), immaturity-related conditions (RR 2.96), asphyxia (RR 2.43), sudden infant death syndrome (RR 7.15), infection (RR 8.32) and external causes (RR 7.30). Maternal characteristics accounted for only a small part of the risk disparities. Substantial risk ratios for preterm birth, stillbirth and infant death remained when the comparisons were restricted to other rural or northern areas of Canada. INTERPRETATION: The Inuit-inhabited areas had much higher rates of preterm birth, stillbirth and infant death compared with the rest of Canada and with other rural and northern areas. There is an urgent need for more effective interventions to improve maternal and infant health in Inuit-inhabited areas.

Suicide mortality by occupation in Canada, 1991-2001.

OBJECTIVE: To describe the association between occupation and risk of suicide among working-age men and women in Canada. METHOD: This study of suicide mortality over an 11-year period is based on a broadly representative 15% sample of the noninstitutionalized population of Canada aged 30 to 69 years at cohort inception. Age-standardized mortality rates (ASMRs) and rate ratios were calculated for men and women in 5 categories of skill level and 80 specific occupational groups, as well as for people not occupationally active. RESULTS: The suicide mortality rate was 20.1/100 000 person years for occupationally active men (during 9 600 000 person years of follow-up) and 5.3/100 000 person years for occupationally active women (during 8 100 000 person years of follow-up). Among occupationally active men, elevated rates of suicide mortality were observed for 9 occupational groups and protective effects were observed for 6 occupational groups. Among women, elevated rates of suicide were observed in 4 occupational groups and no protective effects were observed. For men and women, ASMRs for suicide were inversely related to skill level. CONCLUSIONS: The limited number of associations between occupational groups and suicide risk observed in this study suggests that, with few exceptions, the characteristics of specific occupations do not substantially influence the risk for suicide. There was a moderate gradient in suicide mortality risk relative to occupational skill level. Suicide prevention strategies in occupational settings should continue to emphasize efforts to restrict and limit access to lethal means, one of the few suicide prevention policies with proven effectiveness.

Avoidable mortality for causes amenable to medical care, by occupation in Canada, 1991-2001.

OBJECTIVE: To describe the incidence of avoidable mortality for causes amenable to medical care among occupation groups in Canada. METHOD: A cohort study over an 11-year period among a representative 15% sample of the non-institutionalized population of Canada aged 30-69 at cohort inception. Age-standardized mortality rates for causes amenable to medical care and all other causes of death were calculated for occupationally-active men and women in five categories of skill level and 80 specific occupational groups as well as for persons not occupationally active. RESULTS: Age-standardized mortality rates per 100,000 person-years at risk for causes amenable to medical care and for all other causes were 132.3 and 218.6, respectively, for occupationally-active women, and 216.6 and 449.3 for occupationally-active men. For causes amenable to medical care and for all other causes, for both sexes, there was a gradient in mortality relative to the five-level ranking by occupational skill level, but the gradient was less strong for women than for men. Across the 80 occupation minor groups, for both men and women, there was a linear relationship between the rates for causes amenable to medical care and the rates for all other causes. CONCLUSIONS: For occupationally-active adults, this study found similar gradients in mortality for causes amenable to medical care and for all other causes of mortality over the period 1991-2001. Avoidable mortality is a valuable indicator of population health, providing information on outcomes pertinent to the organization and delivery of health care services.

Investigating socio-economic disparities in preterm birth: evidence for selective study participation and selection bias.

Selective study participation can theoretically lead to selection bias. We explored this issue in the context of a multicentre cohort study of socio-economic disparities in preterm birth. Women with singleton pregnancies were recruited from four large Montreal maternity hospitals and invited to return for an interview, vaginal examination and venepuncture at 24-26 weeks of gestation. We compared the observed preterm birth rate (ultrasound confirmed) among the 5146 cohort women to that expected based on all 108 724 Montreal Census Metropolitan Area (CMA) singleton births for 1998-2000. The observed preterm birth rate in the study cohort was 5.1%, compared with 6.3% in the CMA (P < 0.001) (unadjusted morbidity ratio [95% CI] = 0.80 [0.71, 0.90]). Within each stratum of maternal education and neighbourhood income (the latter based on postal code matched links to the 2001 Canadian census), cohort women had substantially lower rates of preterm birth than women from the CMA. No significant association between socio-economic status (SES) and preterm birth was observed in the study cohort, except among 'indicated' (non-spontaneous) cases. The association between neighbourhood income and preterm birth was biased to the null in the study cohort, with adjusted odds ratios in the poorest vs. richest quintiles of 1.01 [0.63, 1.64] in the cohort vs. 1.28 [1.18, 1.39] in the CMA, although no such bias was observed for the association with maternal education assessed at the individual level. We speculate that the lower-than-expected preterm birth rate and attenuated association between neighbourhood income and preterm birth may be related to selective participation by women more psychologically invested in their pregnancies. Investigators should consider the potential for biased associations in pregnancy/birth cohort studies, especially associations based on SES or race/ethnicity, and carry out sensitivity analyses to gauge their effects.

Degree of rural isolation and birth outcomes.

Little is known about how birth outcomes vary in rural areas by degree of rural isolation. We conducted a retrospective cohort study of all births in Quebec, 1991-2000 to assess birth outcomes by the degree of rural isolation according to metropolitan influence as measured by work force commuting flows between rural and urban areas. Compared with urban areas, crude risks of preterm birth, small-for-gestational age birth, stillbirth, neonatal death and postneonatal death were similar in rural areas with strong metropolitan influence, but were significantly higher for preterm birth, stillbirth and postneonatal death in rural areas with weak or no metropolitan influence, and for neonatal death in rural areas with no metropolitan influence. Adjustment for maternal characteristics (age, mother tongue, education, marital status, parity, plurality and infant sex) attenuated the associations. The adjusted odds ratios [95% confidence intervals] were 1.36 [1.12, 1.64] for stillbirth in rural areas with weak metropolitan influence, 1.63 [1.14, 2.32] for neonatal death in rural areas with no metropolitan influence, 1.78 [1.21, 2.63] and 1.37 [1.07, 1.75] for postneonatal death in rural areas with weak and no metropolitan influence, respectively. Much higher neonatal death rates were observed for preterm or low-birthweight babies in rural areas with no metropolitan influence, suggesting inadequate access to optimal neonatal care. We conclude that birth outcomes in rural areas differ according to the degree of rural isolation. Fetuses and infants of mothers from rural areas with weak or no metropolitan influence are particularly vulnerable to the risks of death during the perinatal and postnatal periods.

Does one size fit all? The case for ethnic-specific standards of fetal growth.

BACKGROUND: Birth weight for gestational age is a widely-used proxy for fetal growth. Although the need for different standards for males and females is generally acknowledged, the physiologic vs pathologic nature of ethnic differences in fetal growth is hotly debated and remains unresolved. METHODS: We used all stillbirth, live birth, and deterministically linked infant deaths in British Columbia from 1981 to 2000 to examine fetal growth and perinatal mortality in Chinese (n = 40,092), South Asian (n = 38,670), First Nations, i.e., North American Indian (n = 56,097), and other (n = 731,109) births. We used a new analytic approach based on total fetuses at risk to compare the four ethnic groups in perinatal mortality, mean birth weight, and "revealed" (< 10th percentile) small-for-gestational age (SGA) among live births based on both a single standard and four ethnic-specific standards. RESULTS: Despite their lower mean birth weights and higher SGA rates (when based on a single standard), Chinese and South Asian infants had lower perinatal mortality risks throughout gestation. The opposite pattern was observed for First Nations births: higher mean birth weights, lower revealed SGA rates, and higher perinatal mortality risks. When SGA was based on ethnic-specific standards, however, the pattern was concordant with that observed for perinatal mortality. CONCLUSION: The concordance of perinatal mortality and SGA rates when based on ethnic-specific standards, and their discordance when based on a single standard, strongly suggests that the observed ethnic differences in fetal growth are physiologic, rather than pathologic, and make a strong case for ethnic-specific standards.

Adverse birth outcomes in relation to maternal marital and cohabitation status in Canada.

PURPOSE: An increasing percentage of children are born to couples who cohabit but are not legally married. Using data from a nationally representative Canadian sample, we estimated associations of maternal marital and cohabitation status with stillbirth, infant mortality, preterm birth (PTB), and small- and large-for-gestational-age (SGA and LGA) birth. METHODS: The 2006 Canadian Birth-Census Cohort was created by linking birth registration data with the 2006 long-form census. We used log-binomial regression to estimate risk ratios (RRs) for adverse birth outcomes associated with being single or living with a common-law partner. Analyses were adjusted for maternal age and education. RESULTS: Data were analyzed for 130,931 singleton births. Adjusted RRs (95% confidence intervals) for single mothers compared with married mothers were 1.92 (1.51-2.42) for stillbirth, 2.08 (1.55-2.81) for infant mortality, 1.36 (1.27-1.46) for PTB, 1.31 (1.22-1.39) for SGA birth, and 0.95 (0.90-1.01) for LGA birth. Adjusted RRs for cohabiting mothers compared with married mothers were 0.93 (0.74-1.16) for stillbirth, 1.05 (0.81-1.35) for infant mortality, 1.09 (1.03-1.15) for PTB, 1.05 (0.99-1.10) for SGA birth, and 0.96 (0.92-1.00) for LGA birth. CONCLUSIONS: In a nationally representative Canadian birth cohort, cohabiting and legally married women experienced similar birth outcomes, but most outcomes for single women were substantially worse.

Avoidable mortality by neighbourhood income in Canada: 25 years after the establishment of universal health insurance.

AIM: To examine neighbourhood income differences in deaths amenable to medical care and public health over a 25-year period after the establishment of universal insurance for doctors and hospital services in Canada. METHODS: Data for census metropolitan areas were obtained from the Canadian Mortality Database and population censuses for the years 1971, 1986, 1991 and 1996. Deaths amenable to medical care, amenable to public health, from ischaemic heart disease and from other causes were considered. Data on deaths were grouped into neighbourhood income quintiles on the basis of the census tract percentage of population below Canada's low-income cut-offs. RESULTS: From 1971 to 1996, differences between the richest and poorest quintiles in age-standardised expected years of life lost amenable to medical care decreased 60% (p<0.001) in men and 78% (p<0.001) in women, those amenable to public health increased 0.7% (p = 0.94) in men and 20% (p = 0.55) in women, those lost from ischaemic heart disease decreased 58% in men and 38% in women, and from other causes decreased 15% in men and 9% in women. Changes in the age-standardised expected years of life lost difference for deaths amenable to medical care were significantly larger than those for deaths amenable to public health or other causes for both men and women (p<0.001). CONCLUSIONS: Reductions in rates of deaths amenable to medical care made the largest contribution to narrowing socioeconomic mortality disparities. Continuing disparities in mortality from causes amenable to public health suggest that public health initiatives have a potentially important, but yet un-realized, role in further reducing mortality disparities in Canada.

Effect of neighbourhood income and maternal education on birth outcomes: a population-based study.

BACKGROUND: Maternal socioeconomic status (SES) is an important determinant of inequity in maternal and fetal health. We sought to determine the extent to which associations between adverse birth outcomes and SES can be identified using individual-level measures (maternal level of education) and community-level measures (neighbourhood income). METHODS: In Quebec, the birth registration form includes a field for the mother's years of education. Using data from birth registration certificates, we identified all births from 1991 to 2000. Using maternal postal codes that can be linked to census enumeration areas, we determined neighbourhood income levels that reflect SES. RESULTS: Lower levels of both maternal education and neighbourhood income were associated with elevated crude risks of preterm birth, small-for-gestational-age (SGA) birth, stillbirth and neonatal and postneonatal death. The effects of maternal education were stronger than, and independent of, those of neighbourhood income. Compared with women in the highest neighbourhood income quintile, women in the lowest quintile were significantly more likely to have a preterm birth (adjusted odds ratio [OR] 1.14, 95% confidence interval [CI] 1.10-1.17), SGA birth (OR 1.18, 95% CI 1.15-1.21) or stillbirth (OR 1.30, 95% CI 1.13-1.48); compared with mothers who had completed community college or at least some university, mothers who had not completed high school were significantly more likely to have a preterm birth (adjusted OR 1.48, 95% CI 1.44-1.52), SGA birth (OR 1.86, 95% CI 1.82-1.91) or stillbirth (OR 1.54, 95% CI 1.36-1.74). INTERPRETATION: Individual and, to a lesser extent, neighbourhood-level SES measures are independent indicators for subpopulations at risk of adverse birth outcomes. Women with lower education levels and those living in poorer neighbourhoods are more vulnerable to adverse birth outcomes and may benefit from heightened clinical vigilance and counselling.

Customized birth weight for gestational age standards: Perinatal mortality patterns are consistent with separate standards for males and females but not for blacks and whites.

BACKGROUND: Some currently available birth weight for gestational age standards are customized but others are not. We carried out a study to provide empirical justification for customizing such standards by sex and for whites and blacks in the United States. METHODS: We studied all male and female singleton live births and stillbirths (22 or more weeks of gestation; 500 g birth weight or over) in the United States in 1997 and 1998. White and black singleton live births and stillbirths were also examined. Qualitative congruence between gestational age-specific growth restriction and perinatal mortality rates was used as the criterion for identifying the preferred standard. RESULTS: The fetuses at risk approach showed that males had higher perinatal mortality rates at all gestational ages compared with females. Gestational age-specific growth restriction rates based on a sex-specific standard were qualitatively consistent with gestational age-specific perinatal mortality rates among males and females. However, growth restriction patterns among males and females based on a unisex standard could not be reconciled with perinatal mortality patterns. Use of a single standard for whites and blacks resulted in gestational age-specific growth restriction rates that were qualitatively congruent with patterns of perinatal mortality, while use of separate race-specific standards led to growth restriction patterns that were incompatible with patterns of perinatal mortality. CONCLUSION: Qualitative congruence between growth restriction and perinatal mortality patterns provides an outcome-based justification for sex-specific birth weight for gestational age standards but not for the available race-specific standards for blacks and whites in the United States.

Infant mortality among First Nations versus non-First Nations in British Columbia: temporal trends in rural versus urban areas, 1981-2000.

BACKGROUND: Increasingly more First Nations (FN) people have moved from rural to urban areas. It is unknown how disparities in infant mortality among FN versus non-FN women have changed over time in urban versus rural areas. METHODS: We conducted a birth cohort-based study of all 877 925 live births (56 771 FN and 821 154 non-FN) registered in British Columbia, 1981-2000. Main outcomes included rates, risk differences, and relative risks of neonatal, postneonatal, and overall infant death. RESULTS: Both neonatal and postneonatal mortality rates for FN infants showed a steady decline in rural areas but a rise-and-fall pattern in urban areas. Relative risks for overall infant death among FN versus non-FN infants declined steadily from 2.75 (95% CI: 2.04, 3.72) to 1.87 (95% CI: 1.24, 2.81) in rural areas from 1981-1984 to 1997-2000, but rose from 1.59 (95% CI: 1.27, 1.99) (1981-1984) to 2.80 (2.33-3.37) (1989-92) and then fell to 1.89 (1.44-2.49) (1997-2000) in urban areas. Risk differences for neonatal death among FN versus non-FN infants declined substantially over time in rural but not urban areas. The disparities in neonatal death among FN versus non-FN were largely explained by differences in preterm birth, while the disparities in postneonatal death were not explained by observed maternal and pregnancy characteristics. CONCLUSIONS: Reductions in disparities in infant mortality among FN versus non-FN women have been less substantial and consistent over time in urban versus rural areas of British Columbia, suggesting the need for greater attention to FN maternal and infant health in urban areas.

Disparities in pregnancy outcomes according to marital and cohabitation status.

OBJECTIVE: To assess the risks and trends of adverse pregnancy outcomes among mothers in common-law unions versus traditional marriage relationships. METHODS: We conducted a birth cohort-based study of all 720,586 births registered in Quebec for the years 1990 to 1997. RESULTS: The proportion of births to common-law mothers more than doubled from 20% in 1990 to 44% in 1997. Preterm birth, low birth weight, small for gestational age, and neonatal and postneonatal mortality rates increased progressively from mothers legally married, to common-law unions, to lone mothers with father information, to lone mothers without father information on birth registrations. Adjusted odd ratios with 95% confidence intervals (CIs) for common-law versus legally married mothers were 1.14 (95% CI 1.11, 1.17) for preterm birth, 1.21 (95% CI 1.18, 1.25) for low birth weight, 1.18 (95% CI 1.16, 1.20) for small for gestational age, 1.07 (95% 0.97, 1.19) for neonatal death, and 1.23 (95% CI 1.04, 1.44) for postneonatal death after controlled for observed individual- and community-level characteristics. The crude and adjusted odds ratios were virtually unchanged over time. CONCLUSION: Pregnancy outcomes are worse among mothers in common-law unions versus traditional marriage relationships but better than among mothers living alone. Modest disparities in pregnancy outcomes in common-law versus traditional marriage relationships have persisted despite the striking rise in common-law unions. LEVEL OF EVIDENCE: II-2