temporal trends in maternal mortality in canada i: estimates based on vital statistics data

OCTOBER JOGC OCTOBRE 2011 l 1011

Temporal Trends in Maternal Mortality in Canada I: Estimates Based on Vital Statistics DataSarka Lisonkova, MD, PhD,1 Sharon Bartholomew, MHSc,2 Jocelyn Rouleau,2 Shiliang Liu, MB, PhD,2 Robert M. Liston, MB,1 K.S. Joseph, MD, PhD1,3; for the Maternal Health Study Group of the Canadian Perinatal Surveillance System1Department of Obstetrics and Gynaecology, University of British Columbia and the Children’s and Women’s Hospital of British Columbia, Vancouver BC

2 Maternal and Infant Health Section, Health Surveillance and Epidemiology Division, Public Health Agency of Canada, Ottawa ON3School of Population and Public Health, University of British Columbia, Vancouver BC

WOMEN’S HEALTH

Key Words: Maternal mortality, trend, Vital Statistics, Canada

Competing Interests: None declared .

Received on April 11, 2011

Accepted on June 13, 2011

Abstract

Objectives: Vital Statistics and World Health Organization reports show a recent increase in maternal mortality in Canada . We carried out a study of temporal trends, regional variations, and causes of death in Canadian maternal mortality using Vital Statistics data .

Methods: We used Vital Statistics death registrations to ascertain maternal deaths between 1981 and 2007 . Maternal mortality rates, risk ratios, and 95% confidence intervals were estimated, and the Cochran-Armitage test was used to evaluate temporal trends . We used hospitalization data from the Canadian Institute for Health Information from 1996 to 2007 to confirm maternal mortality trends observed in the Vital Statistics data .

Results: Maternal mortality rates increased significantly from 4 .5 (95% CI 3 .3 to 5 .8) in 1981 to 1983 to 4 .7 (95% CI 3 .5 to 6 .2) in 1996 to 1998 and to 7 .2 (95% CI 5 .7 to 9 .0) per 100 000 live births in 2005 to 2007 (P value for trend < 0 .001) . The most common causes of maternal death were diseases of the circulatory system, obstetric embolism (venous thromboembolism and amniotic fluid embolism), and hypertension . Deaths due to diseases of the circulatory system and puerperal infection increased significantly from 1981 to 2007 . Maternal mortality rates in the hospitalization data were higher and did not show an increase over time . Provincial and territorial maternal mortality rates from Vital Statistics data showed varying degrees of under-ascertainment (12% to 70%) compared with hospitalization data .

Conclusion: Temporal increases in maternal mortality in Canada observed in Vital Statistics data do not correspond with stable temporal trends observed in hospitalization data, and appear to be an artefact of changes in the coding and ascertainment of maternal deaths .

Résumé

Objectifs : Des rapports du Bureau de l’état civil et de l’Organisation mondiale de la santé indiquent une récente hausse de la mortalité maternelle au Canada . Nous avons mené une étude des tendances temporelles, des variations régionales et des causes de décès en matière de mortalité maternelle au Canada au moyen de données issues du Bureau de l’état civil .

Méthodes : Nous avons utilisé les enregistrements de décès du Bureau de l’état civil pour déterminer les décès maternels entre 1981 et 2007 . Les taux de mortalité maternelle, les risques relatifs et les intervalles de confiance à 95% ont été estimés, et nous avons eu recours au test de Cochran-Armitage pour évaluer les tendances temporelles . Nous avons utilisé les données d’hospitalisation émises par l’Institut canadien d’information sur la santé entre 1996 et 2007 pour confirmer les tendances de mortalité maternelle constatées dans les données du Bureau de l’état civil .

Résultats : Les taux de mortalité maternelle ont connu une hausse significative en passant de 4,5 (IC à 95 %, 3,3 – 5,8) pour la période 1981 - 1983 à 4,7 (IC à 95 %, 3,5 – 6,2) pour la période 1996 - 1998 et à 7,2 (IC à 95 %, 5,7 – 9,0) par 100 000 naissances vivantes pour la période 2005 - 2007 (valeur P pour la tendance < 0,001) . Les causes les plus courantes de décès maternel étaient les maladies du système circulatoire, l’embolie obstétricale (thromboembolie veineuse et embolie du liquide amniotique) et l’hypertension . Les décès attribuables aux maladies du système circulatoire et à l’infection puerpérale ont connu une hausse significative entre 1981 et 2007 . Les taux de mortalité maternelle dérivés des données d’hospitalisation étaient plus élevés et ne connaissaient pas de hausse avec le temps . Les taux provinciaux et territoriaux de mortalité maternelle dérivés des données du Bureau de l’état civil indiquaient divers degrés de sous-détermination (de 12 % à 70 %), par comparaison avec les données d’hospitalisation .

Conclusion : Les hausses temporelles des taux de mortalité maternelle au Canada que permettent de constater les données du Bureau de l’état civil ne correspondent pas avec les tendances temporelles stables que permettent de constater les données d’hospitalisation et semblent constituer un artéfact des modifications du codage et de la détermination des décès maternels .

J Obstet Gynaecol Can 2011;33(10):1011-1019

1012 l OCTOBER JOGC OCTOBRE 2011

WOMEN’S HEALTH

INTRODUCTION

The United Nations Millennium Declaration in 2000, which established the target of reducing the 1990 rate

of global maternal mortality by 75% by 2015 (Millennium Development Goal 5),1 spurred a revival of interest in international maternal mortality rates. Unfortunately, there has not been sufficient progress towards achieving this goal to date, especially in sub-Saharan Africa. Progress has been slow in developed countries as well; maternal mortality rates in these countries decreased from 16 per 100 000 live births in 1990 to 14 per 100 000 live births in 2008, reflecting an annual decline of 0.8% (compared with the 5.5% overall global decline required to meet Millennium Development Goal 5).2

Unexpected temporal trends in maternal mortality have emerged in some developed countries.3 In recent years, Canada, the Netherlands, the United Kingdom, and the United States have reported increases in maternal mortality rates.2–6 World Health Organization reports, based on vital statistics data, estimated that maternal mortality in the United States increased from 12 to 24 per 100 000 live births,2 while Canadian maternal mortality rates increased from 6 to 12 per 100 000 live births from 1990 to 2008.2 Similarly, according to the Confidential Enquiry into Maternal and Child Health, maternal mortality in the United Kingdom rose from 9.8 to 14.0 per 100 000 maternities from 1985–1987 to 2003–2005,5 and then declined to 11.4 in 2006–20087; in the Netherlands, rates increased from 9.7 to 12.1 per 100 000 live births from 1983–1992 to 1993–2005.6

Given this unexpected increase in maternal mortality, we carried out a study examining temporal trends in maternal mortality in Canada using Vital Statistics data. We also examined regional variations in maternal mortality, age-specific maternal mortality rates, and the underlying causes of death. Finally, we attempted to obtain insights into the accuracy of maternal mortality rate estimates by contrasting the temporal trend in maternal mortality rates obtained from Vital Statistics data with that obtained from hospitalization data.

METHODS

We used Vital Statistics data to estimate temporal trends in maternal mortality in Canada from 1981 to 2007. Registration of death is mandatory in Canada, and the registration form consists of two parts: the first includes personal information obtained from a relative of the deceased, and the second—the medical certificate–includes medical information completed by the medical practitioner

or by a coroner if an inquest or medical enquiry was held. We obtained information about maternal age, residence (province or territory), date of death, underlying cause of death, and place where death occurred (hospital or other).8

Maternal death is defined by the International Classification of Diseases (ICD; versions 9 and 10) as “the death of a woman while pregnant or within 42 days of termination of pregnancy, irrespective of duration and site of the pregnancy, from any cause related to or aggravated by the pregnancy or its management” but not from accidental or incidental causes.9 Maternal deaths in this study were defined as those with an underlying cause of death including ICD-9 codes 630–676 and ICD-10 codes O00-O99. Deaths identified by the ICD-10 codes O96 and O97 were labelled late maternal deaths (maternal deaths occurring 43 to 365 days after pregnancy termination and deaths due to direct obstetric causes occurring one year or more after delivery); such deaths could not be identified from 1981 to 1999 because such a code was not part of ICD-9, and accordingly they were not included in the evaluation of temporal trends.

The maternal mortality rate was calculated as the number of maternal deaths per 100 000 live births (also termed the maternal mortality ratio). The number of live births by period, province or territory of residence, and maternal age category was obtained from Vital Statistics registrations of births. Maternal mortality rates and 95% confidence intervals10 were calculated for each time period (three-year intervals from 1981 to 2007), province or territory, maternal age, and underlying cause of death. Exact binomial confidence intervals11 were used for cause-specific maternal mortality rates. Maternal mortality risk ratios (RR) and 95% confidence intervals were also calculated to estimate the magnitude of the differences between levels of these factors. Diagnostic codes for the underlying causes of death (ICD-9 and ICD-10) are included in the Appendix. Information about place of maternal death was not available for the province of Quebec for years 2001 to 2007. The Cochran-Armitage test for linear trend in proportions was used to assess the statistical significance of temporal trends.10 P values less than 0.05 were considered statistically significant, and no adjustment was made for multiple comparisons. Data analyses were performed using SAS software, version 9.2 (SAS Institute Inc., Cary NC).

It is widely acknowledged that the number of maternal deaths is typically underestimated by the Vital Statistics death registration system when compared with more comprehensive methods of case ascertainment.2,5,12 To address this potential limitation of vital registration, we used hospitalization data from the Canadian Institute for Health


Temporal Trends in Maternal Mortality in Canada I: Estimates Based on Vital Statistics Data

Information to confirm the temporal trends observed in the Vital Statistics data. The Canadian Institute for Health Information collects information, including demographic and clinical data, about all hospitalizations in Canada. Hospitalization records were abstracted from medical charts and then compiled into the Discharge Abstract Database; the individual records contain an encrypted personal health number. Using the Discharge Abstract Database, we identified as maternal deaths hospital deaths occurring during delivery or termination of pregnancy. Additional maternal and late maternal deaths were identified by linking all other hospital deaths among women of reproductive age (15 to 54 years) to previous hospitalizations within 42 days or from 43 to 365 days prior to death. Diagnoses related to childbirth or pregnancy (ICD-9 codes 630–676, and ICD-10 codes O00-O99) on these internally linked hospitalization records were used to identify maternal deaths (within 42 days), or late maternal deaths (between 43 and 365 days, or those including code O96 or O97). Maternal mortality rates in the hospitalization data were calculated as the number of maternal deaths per 100 000 live births. Data from Quebec and Manitoba were excluded from these additional analyses, because of absent (Quebec) or incomplete (Manitoba, past years) hospitalization data in the Discharge Abstract Database. Details regarding case ascertainment in the hospitalization data are provided elsewhere.13

RESULTS

The maternal mortality rate based on Vital Statistics data was 4.5 per 100 000 live births (95% CI 4.1 to 5.0) during the study period (1981 to 2007); the lowest rate was observed

in 1982 (1.9; 95% CI 0.7 to 3.8) and the highest in 2005 (8.2 per 100 000 live births, 95% CI 5.5 to 11.8). Maternal mortality rates remained relatively stable (approximately 4 deaths per 100 000 live births) from 1981–1983 to 1999–2001, and then increased to approximately 7 per 100 000 live births in 2005–2007. The overall increase in maternal mortality from 1981 to 2007 was statistically significant (P for linear trend < 0.001, Table 1).

Maternal mortality increased with age (Table 2). Mothers aged 20 to 24 years had the lowest maternal mortality rate, 2.7 per 100 000 live births (95% CI 2.2 to 3.3), and mothers aged 35 to 39 and 40 to 49 years had significantly higher rates of maternal death. There was no significant temporal trend in age-specific maternal mortality rates, with the exception of mothers aged 40 to 49 years. These mothers showed a significant decline in maternal mortality from 1981–1989 (33.4 per 100 000 live births) to 1990–1998 (18.5) and to 1999–2007 (10.9) (P for trend 0.02). The maternal mortality risk ratio comparing older and younger mothers (40 to 49 vs. 20 to 24 years of age) was lowest in the most recent period, 1999 to 2007 (RR 2.7; 95% CI 1.2 to 5.9), compared with previous periods (11.7; 95% CI 5.3 to 26.0 in 1981–1989 and 13.4; 95% CI 5.3 to 33.8 in 1990–1998) (Table 3).

Maternal mortality rates differed by province or territory of residence, ranging from 2.4 per 100 000 live births (95% CI 1.2 to 5.1) in Nova Scotia to 12.1 per 100 000 live births (95% CI 6.7 to 21.9) in Newfoundland and Labrador (Table 4). No maternal deaths were reported from Prince Edward Island, Yukon, or Nunavut. A significant temporal increase in the maternal death rate was observed in Ontario, where maternal mortality rates rose from 4.9 (95% CI 3.3 to 5.6) in 1981–1989 to 5.1 (95% CI 4.1 to 6.2) in 1990–1999 and to 9.5 (95% CI 7.8 to 11.6) per 100 000 live births in 2000–2007 (P for trend < 0.001).

The most common causes of maternal death from 1981 to 2007 were diseases of the circulatory system, obstetric embolism (including venous thromboembolism and amniotic fluid embolism), and hypertensive complications of pregnancy and delivery (1.0; 95% CI 0.8 to 1.2; 0.7; 95% CI 0.5 to 0.9; and 0.6; 95% CI 0.5 to 0.8 per 100 000 live births, respectively) (Table 5). There was a significant increase in maternal deaths caused by major puerperal infection (P for trend 0.004) and diseases of the circulatory system (P for trend < 0.001). There were increases in the number of maternal deaths caused by “other complication of pregnancy, not otherwise specified” and “other indirect causes of death” (P for trend 0.001 and 0.002, respectively); however, heterogeneity within these codes and differences between ICD-9 and ICD-10 imply poor comparability between the maternal mortality rates of earlier and more recent years.

Table 1. Maternal mortality rates, excluding late maternal deaths, Vital Statistics, Canada, 1981 to 2007

Deaths

Live births

Maternal mortality rate per

100 000 live births (95% CI)

1981 to 1983 050 1 118 117 4 .47 (3 .32 to 5 .85)

1984 to 1986 038 1 125 671 3 .38 (2 .40 to 4 .66)

1987 to 1989 049 1 139 198 4 .30 (3 .19 to 5 .68)

1990 to 1992 041 1 206 650 3 .40 (2 .42 to 4 .59)

1993 to 1995 046 1 151 502 3 .99 (2 .90 to 5 .28)

1996 to 1998 050 1 057 180 4 .73 (3 .51 to 6 .21)

1999 to 2001 042 1 998 844 4 .20 (3 .06 to 5 .68)

2002 to 2004 055 1 001 076 5 .49 (4 .16 to 7 .16)

2005 to 2007 077 1 064 657 7 .23 (5 .74 to 9 .00)

1981 to 2007 448 9 862 895 4 .54 (4 .14 to 4 .98)Cochran-Armitage test for trend: P < 0 .001


WOMEN’S HEALTH

Most maternal deaths occurred in hospital (88.4%); other places of death were not specified. This proportion was stable from 1991 to 2007 (data were available only for this period) with no apparent trend. Late maternal deaths were not reported in the Vital Statistics database prior to 2000, because they were not captured by ICD-9 (this category was introduced in ICD-10). Eleven late maternal deaths were reported between 2000 and 2007. The late maternal mortality rate was 0.4 per 100 000 live births during this period (95% CI 0.2 to 0.7), fluctuating between 0.0 and 0.8 per 100 000 live births per year with no apparent trend.

Analyses comparing temporal trends in maternal mortality from 1996 to 2007 using two different sources of data (Vital Statistics and hospitalization data) showed very different patterns (Figure). The significant increase in the maternal death rate observed in Vital Statistics data was not evident when maternal mortality rates were calculated using hospitalization data. The discrepancy between these two sources of case ascertainment was significant in the earlier

years (RR 1.6; 95% CI 1.1 to 2.3 in 1996–1998 and 2.0; 95% CI 1.1 to 2.3 in 1999–2001), as opposed to recent years when both data sources yielded similar results (RR 1.3; 95% CI 0.9 to 1.9 in 2002–2004 and 1.1; 95% CI 0.8 to 1.5 in 2005–2007). Comparisons of provincial or territorial maternal mortality rates (based on place of residence in the Vital Statistics data and on place of occurrence in the hospitalization data) showed that potential underreporting in Vital Statistics data from 1996 to 2007 ranged from 12% in Ontario to 70% in Newfoundland and Labrador. The temporal convergence in maternal mortality rates from the two data sources suggests improved ascertainment of maternal deaths in Vital Statistics data in recent years, which is likely associated with the introduction of ICD-10.

Late maternal death rates also differed substantially between Vital Statistics and hospitalization data: 0.4 (95% CI 0.2 to 0.7) deaths per 100 000 live births based on Vital Statistics data versus 5.4 (95% CI 4.6 to 6.3) deaths per 100 000 live births based on hospitalization data for the years 2000 to 2007.

Table 2. Age-specific MMR per 100 000 live births, excluding late maternal deaths, Vital Statistics Canada, 1981 to 1989, 1990 to 1998, and 1999 to 2007

1981 to 1989 1990 to 1998 1999 to 2007 1981 to 2007

Age, years MMR 95% CI MMR 95% CI MMR 95% CI P* MMR 95% CI

15 to 19 05 .13 3 .12 to 8 .42 02 .46 1 .18 to 5 .14 04 .27 2 .18 to 8 .36 0 .573 05 .13 2 .78 to 5 .60

20 to 24 02 .86 2 .06 to 3 .97 01 .38 0 .80 to 2 .38 04 .06 2 .83 to 5 .81 0 .348 02 .69 2 .15 to 3 .35

25 to 29 03 .04 2 .34 to 3 .96 02 .99 2 .26 to 3 .95 04 .24 3 .27 to 5 .50 0 .149 03 .36 2 .88 to 3 .92

30 to 34 05 .18 3 .95 to 6 .78 04 .80 3 .77 to 6 .10 05 .31 4 .21 to 6 .70 0 .872 05 .08 4 .41 to 5 .86

35 to 39 08 .86 05 .95 to 13 .20 09 .30 06 .95 to 12 .43 10 .98 08 .66 to 13 .92 0 .384 09 .96 08 .43 to 11 .78

40 to 49 33 .44 18 .69 to 59 .82 18 .46 10 .67 to 31 .93 10 .90 06 .30 to 18 .85 0 .019 16 .74 12 .13 to 23 .12

15 to 49 04 .15 3 .60 to 4 .77 04 .03 3 .50 to 4 .64 05 .68 5 .02 to 6 .44 0 .005 04 .59 4 .24 to 4 .96MMR: maternal mortality rate per 100 000 live births

*Cochran-Armitage test for trend

Live births among mothers < 15 and > 49 years of age and births with missing maternal age were excluded, hence MMR for years 1981 to 2007 differs slightly from that provided in Table 1 .

Table 3. Maternal mortality rate ratio, excluding late maternal deaths, Vital Statistics Canada, 1981 to 1989, 1990 to 1998, and 1999 to 2007

1981 to 1989 1990 to 1998 1999 to 2007 1981 to 2007

Age, years RR 95% CI RR 95% CI RR 95% CI RR 95% CI

15 to 19 01 .8 0 .9 to 3 .6 01 .8 0 .6 to 5 .3 1 .1 0 .4 to 2 .6 1 .5 0 .9 to 2 .4

20 to 24 Reference Reference Reference Reference

25 to 29 01 .1 0 .6 to 1 .8 02 .2 1 .0 to 4 .5 1 .0 0 .6 to 1 .8 1 .2 0 .9 to 1 .7

30 to 34 01 .8 1 .1 to 3 .0 03 .5 1 .7 to 7 .1 1 .3 0 .8 to 2 .2 1 .9 1 .4 to 2 .6

35 to 39 03 .1 1 .7 to 5 .7 06 .8 03 .2 to 14 .1 2 .7 1 .6 to 4 .5 3 .7 2 .7 to 5 .2

40 to 49 11 .7 05 .3 to 26 .0 13 .4 05 .3 to 33 .8 2 .7 1 .2 to 5 .9 6 .2 3 .9 to 9 .9



DISCUSSION

Vital Statistics data show that 448 women died from diseases or conditions caused or aggravated by pregnancy, childbirth, or the puerperium from 1981 to 2007 in Canada. This yields a maternal mortality rate of 4.5 (95% CI 4.1 to 5.0) per 100 000 live births. Maternal mortality rates remained relatively stable from 1981 to 2001 (4.5 and 4.2 per 100 000 live births in 1981–1983 and 1999–2001, respectively), but increased significantly from 2001 to 2007 (to 7.2 per 100 000 live births in 2005–2007). However, this increase in maternal mortality was not observed when hospitalization data were used to ascertain temporal trends in maternal deaths.

The discrepancy in the number of maternal deaths in the Vital Statistics data versus the hospitalization data was larger during the earlier years (1996 to 2001) and gradually diminished during more recent years (2002 to 2007). The apparent improvement in Vital Statistics data coincided with the introduction of the 10th version of the International Classification of Diseases (in 2000 to 2001). ICD-10 placed greater emphasis on detailed coding of pregnancy-related conditions and introduced a new definition of late maternal death. Thus the increase in maternal mortality rates based on Vital Statistics data is likely a result of a temporal improvement in case ascertainment. A similar phenomenon has been observed in the United

States, where the maternal death rate increased from 12.2 to 15.4 per 100 000 live births from 1998 to 2005, with an apparent rise in maternal mortality rates after 2000. Another apparent increase in maternal mortality rates in the United States was observed after 2003, when new vital registration forms were introduced, including a check-box on death certificates indicating a recent pregnancy.14,15

Vital registration is used to report maternal mortality and monitor its trends in the majority of developed countries.2 In Canada, vital registration of deaths occurs through a uniform, legislated process of data collection in all provinces and territories.8 Coverage of deaths is nearly complete, as documented by studies evaluating the accuracy of data capturing and coding.16,17 Only one underlying cause of death is indicated on each death record, using the ICD codes, and this facilitates national and international comparisons of cause-specific mortality. However, because the death certificates were not designed to ascertain maternal death, Vital Statistics data have several limitations when used to estimate the maternal mortality rate or monitor its trend. Several studies have shown that maternal death rates based on vital death registration capture only 40% to 60% of cases.18–22 Because of this known limitation, the World Health Organization reports use of an adjustment coefficient for maternal mortality figures to correct for underreporting.2,23 For Canada, a 60% upward adjustment was used in World Health Organization reports, based on previous estimates of under-ascertainment.12,21 The most recent comprehensive investigation of maternal mortality in Canada was published in 2004. It is noteworthy that only about 40% to 60% of maternal deaths identified by that investigation were identified as maternal deaths in Vital Statistics data.12

We observed a temporal increase in several underlying causes of maternal death, including puerperal infection, diseases of the circulatory system, and other causes. While a significant rise in reports of deaths due to the latter two categories of causes may be a result of coding changes, maternal deaths due to major puerperal infection have increased continuously throughout the whole study period. This suggests the possibility of a true increase in such maternal deaths. Puerperal sepsis is a relatively frequent maternal morbidity (11.3 per 100 000 deliveries; Canada, 2003–2007),24 and even though the incidence of puerperal sepsis declined in Canada from 2003 to 2007,24 a temporal increase in case fatality is possible. The Confidential Enquiries into Maternal Deaths in the United Kingdom identified sepsis as a newly emerging leading cause of direct maternal death in the United Kingdom in 2006–2008.7

Table 4. Maternal mortality rates by province/territory of residence based on Vital Statistics data, Canada, 1981 to 2007 Province/territory

Maternal mortality rate per 100 000 live births

95% CI

Newfoundland and Labrador* 12 .11 (6 .71 to 21 .87)

Nova Scotia 02 .41 (1 .15 to 5 .05)

New Brunswick 03 .84 (2 .00 to 7 .39)

Ontario* 06 .12 (5 .37 to 6 .97)

Manitoba 02 .59 (1 .44 to 4 .69)

Saskatchewan 04 .31 (2 .68 to 6 .93)

Alberta 04 .19 (3 .15 to 5 .58)

British Columbia 03 .94 (2 .95 to 5 .27)

Northwest Territories 06 .02 (1 .50 to 24 .05)

Quebec* 03 .20 (2 .54 to 4 .03)

Canada 04 .54 (4 .14 to 4 .98)*Maternal mortality rate significantly different from the Canadian rate *(P < 0 .05)

No maternal deaths were reported from Yukon, Nunavut, and Prince Edward Island .

The above rates do not include late maternal deaths .


WOMEN’S HEALTH

Tabl

e 5.

Cau

se-s

peci

fic m

ater

nal m

orta

lity

rate

s pe

r 100

000

live

birt

hs (M

MR

), Vi

tal S

tatis

tics

Can

ada,

198

1 to

200

719

81 to

198

619

87 to

199

219

93 to

199

819

99 to

200

420

05 to

200

719

81 to

200

7

Und

erly

ing

caus

e of

dea

th*

MM

R

95%

CI

MM

R

95%

CI

MM

R

95%

CI

MM

R

95%

CI

MM

R

95%

CI

P†

MM

R

95%

CI

Ect

opic

and

mol

ar p

regn

ancy

0 .27

0 .10

to 0

.58

0 .17

0 .05

to 0

.44

0 .41

0 .19

to 0

.77

0 .20

0 .05

to 0

.51

0 .28

0 .06

to 0

.82

0 .87

0 .26

0 .17

to 0

.39

Oth

er p

regn

ancy

with

abo

rtive

ou

tcom

e0 .

130 .

03 to

0 .3

90 .

260 .

09 to

0 .5

60 .

140 .

03 to

0 .4

00 .

100 .

01 to

0 .3

60 .

190 .

02 to

0 .6

80 .

760 .

160 .

09 to

0 .2

6

Ant

epar

tum

hem

orrh

age,

pl

acen

tal a

brup

tion,

and

pl

acen

ta p

revi

a

0 .22

0 .07

to 0

.52

0 .30

0 .12

to 0

.61

0 .50

0 .25

to 0

.89

0 .20

0 .05

to 0

.51

0 .75

0 .32

to 1

.48

0 .10

0 .35

0 .25

to 0

.49

Hyp

erte

nsio

n co

mpl

icat

ing

preg

nanc

y, c

hild

birth

, and

the

puer

periu

m

0 .45

0 .21

to 0

.82

0 .68

0 .39

to 1

.11

0 .77

0 .45

to 1

.23

0 .60

0 .31

to 1

.05

0 .47

0 .15

to 1

.10

0 .81

0 .61

0 .46

to 0

.78

Oth

er c

ompl

icat

ions

of

preg

nanc

y no

t oth

erw

ise

spec

ified

0 .09

0 .01

to 0

.32

0 .00

0 .00

to 0

.16

0 .05

0 .00

to 0

.25

0 .25

0 .08

to 0

.58

0 .56

0 .21

to 1

.23

0 .00

10 .

140 .

08 to

0 .2

4

Nor

mal

del

iver

y an

d ot

her

indi

catio

ns fo

r car

e in

pr

egna

ncy,

labo

ur, a

nd

deliv

ery

0 .00

0 .00

to 0

.16

0 .04

0 .00

to 0

.24

0 .09

0 .01

to 0

.33

0 .10

0 .01

to 0

.36

0 .09

0 .00

to 0

.52

0 .15

0 .06

0 .02

to 0

.13

Pos

tpar

tum

hem

orrh

age

0 .53

0 .28

to 0

.93

0 .34

0 .15

to 0

.67

0 .14

0 .03

to 0

.40

0 .25

0 .08

to 0

.58

0 .28

0 .06

to 0

.82

0 .09

0 .31

0 .21

to 0

.45

Oth

er c

ompl

icat

ions

occ

urrin

g m

ainl

y in

the

cour

se o

f lab

our

and

deliv

ery

not o

ther

wis

e sp

ecifi

ed

0 .58

0 .31

to 0

.99

0 .26

0 .09

to 0

.56

0 .23

0 .07

to 0

.53

0 .15

0 .03

to 0

.44

0 .38

0 .10

to 0

.96

0 .09

0 .31

0 .21

to 0

.45

Maj

or p

uerp

eral

infe

ctio

n0 .

040 .

00 to

0 .2

50 .

130 .

03 to

0 .3

70 .

140 .

03 to

0 .4

00 .

300 .

11 to

0 .6

50 .

470 .

15 to

1 .1

00 .

004

0 .18

0 .11

to 0

.29

Veno

us c

ompl

icat

ions

in

preg

nanc

y an

d th

e pu

erpe

rium

0 .

180 .

05 to

0 .4

60 .

340 .

15 to

0 .6

70 .

140 .

03 to

0 .4

00 .

200 .

05 to

0 .5

10 .

280 .

06 to

0 .8

20 .

990 .

220 .

14 to

0 .3

4

Obs

tetri

c em

bolis

m‡

0 .58

0 .31

to 0

.99

0 .55

0 .30

to 0

.95

0 .86

0 .52

to 1

.34

0 .50

0 .24

to 0

.92

1 .22

0 .65

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.87

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0 .00

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.17

0 .05

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.28

0 .00

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21 to

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380 .

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The maternal death rate increased with maternal age; mothers aged 35 to 39 and 40 to 49 had significantly higher maternal mortality rates than mothers aged 20 to 24. The gap in maternal mortality rates between the younger and the oldest mothers (20 to 24 vs. 40 to 49 years old), however, was lowest in the most recent years, 1999 to 2007 (maternal mortality RR 2.7, compared with 13.4 in 1990–1998, and 11.7 in 1981–1989). The age-specific temporal trends in maternal death rates were not statistically significant, except in mothers aged 40–49 years. A significant decline in the maternal mortality rate among the oldest mothers may have resulted from temporal changes in the maternal characteristics of these women, including increased socioeconomic status, higher educational attainment, and healthier lifestyle. However, it is also possible that maternal deaths among the oldest mothers continue to be underreported, as the underlying cause of death in this age group is likely unrelated to pregnancy (e.g., cardiovascular diseases). Our study has some limitations. As mentioned, maternal deaths identified from Vital Statistics data are subject to under-ascertainment. In Canada, the degree of under-ascertainment differed by time period and by province or territory, hence the analysis of trends and provincial and territorial comparisons of maternal mortality based exclusively on Vital Statistics data may be compromised. For example, the Vital Statistics-based maternal mortality rate in Ontario was higher than the overall rate in Canada, but Ontario Vital Statistics data also had the lowest degree of case under-ascertainment compared with hospitalization data. Thus better case

ascertainment from Vital Statistics data in Ontario may have been responsible for the higher maternal mortality rate in this province. However, our ability to estimate the degree of maternal death under-ascertainment among the provinces and territories was limited, because maternal deaths ascertained using hospitalization data included only hospital cases and were based on place of occurrence (as opposed to maternal deaths ascertained using Vital Statistics data, which were based on place of residence). Publications underlining the importance of accurate case ascertainment of maternal deaths in Canada appeared from 2000 to 2005.12,21 These, together with ICD classification changes, may have contributed to improved case ascertainment in Vital Statistics databases. However, requirements for reporting maternal deaths to a coroner or a medical examiner vary by province or territory,12 and this may contribute to provincial and territorial case ascertainment discrepancies in Vital Statistics data.

Vital Statistics data are not available on a timely basis, and therefore are not suitable for identifying recent changes. In contrast, hospitalization data can serve as a more comprehensive and timely source for monitoring trends in maternal mortality in Canada. Data for the Discharge Abstract Database are collected uniformly from all Canadian provinces and territories except Quebec, and the data have high accuracy for major diagnoses and therapeutic procedures.25,26 Canadian Institute for Health Information hospitalization data have been used

Temporal trends in maternal mortality based on Vital Statistics data and hospitalization data from the Canadian Institute for Health Information Canada (excluding Manitoba and Quebec), 1996 to 2007. The solid line indicates the maternal mortality rate based on hospitalization data; the dashed line shows the maternal mortality rate based on Vital Statistics data.

0

2

4

6

8

10

12

14

1996-98 1999-01 2002-04 2005-07

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s


WOMEN’S HEALTH

successfully by the Canadian Perinatal Surveillance System4 and in previous studies of maternal morbidity and infant health outcomes.24,27–29 However, hospitalization records do not identify an underlying cause of death, which makes it difficult to determine with certainty whether maternity was directly or indirectly related to the cause of death or whether it was incidental. It is also important to note that some age-specific, disease-specific, and provincial and territorial temporal trends and comparisons were not statistically significant, likely because of the small number of maternal deaths in those categories. This underscores the importance of epidemiologic investigations of severe maternal morbidity, as women suffering severe maternal morbidity have substantially higher rates of maternal death.29

CONCLUSION

Our study based on Vital Statistics data shows a significant temporal increase in the maternal mortality rate in Canada. However, this increase is likely due to an improvement in maternal death ascertainment in Vital Statistics death registrations following changes in the coding of maternal death. Vital Statistics-based maternal mortality rates should be used cautiously for evaluating temporal trends and for comparisons between provinces or territories.

ACKNOWLEDGEMENTS

Sarka Lisonkova is supported by a post-doctoral fellowship award from the Michael Smith Foundation for Health Research and K.S. Joseph’s work is supported by the Child and Family Research Institute. Contributing members of the Maternal Health Study Group of the Canadian Perinatal Surveillance System included Juan Andrés León (Public Health Agency of Canada) and Michael Kramer (McGill University).

REFERENCES

1. United Nations Development Programme. Millennium Development Goals. Available at: http://www.undp.org/mdg/goa15.shtml. Accessed March 2011.

2. World Health Organization. Trends in maternal mortality: 1990 to 2008. Geneva: WHO; 2010. WHO Library: ISBN 9789241500265. Available at: http://whqlibdoc.who.int/publications/2010/9789241500265_eng.pdf. Accessed October 2010.

3. Hogan MC, Foreman KJ, Naghavi M, Ahn SY, Wang M, Makela SM, et al. Maternal mortality for 181 countries, 1980–2008: a systematic analysis of progress towards Millennium Development Goal 5. Lancet 2010;375:1609–23.

4. Public Health Agency of Canada. Canadian Perinatal Health Report, 2008 Edition. Catalogue No. HP10–12/2008E. Ottawa: PHAC; 2008. Available at: http://www.phac-aspc.gc.ca/publicat/2008/cphr-rspc/pdf/cphr-rspc08-eng.pdf. Accessed August 8, 2011.

5. Lewis G. The Confidential Enquiry into Maternal and Child Health (CEMACH). Saving mothers’ lives: reviewing maternal deaths to make motherhood safer—2003–2005. The seventh report on confidential enquiries into maternal deaths in the United Kingdom. London: CEMACH; 2007.

6. Shutte JM, Steegers EAP, Schuitemaker NWE, Santem JC, deBoer K, Pel M, et al. Rise in maternal mortality in the Netherlands. BJOG 2010;117:399–406.

7. Centre for Maternal and Child Enquiries (CMACE). Saving mothers’ lives: reviewing maternal deaths to make motherhood safer: 2006–08. The eighth report on Confidential Enquiries into Maternal Deaths in the United Kingdom. BJOG 2011;118(Suppl. 1):1–203.

8. Vital Statistics Canada. Death database: definitions, data sources, methods. Report 3233. Available at: http://www.statcan.gc.ca/cgi-bin/imdb/ p2SV.pl?Function=getSurvey&SDDS=3233&lang=en&db=imdb&adm=8&dis=2. Accessed December 15, 2010.

9. World Health Organization. WHO: health statistics and health information systems. Maternal mortality ratio (per 100 000 live births). Available at: http://www.who.int/healthinfo/statistics/indmaternalmortality/en/index.html. Accessed January 2011.

10. Clayton D, Hills M. Statistical models in epidemiology. New York: Oxford University Press; 1995:78–86.

11. Daly L. Simple SAS macros for calculation of exact binomial and Poisson confidence limits. Comput Biol Med 1992;22:351–461.

12. Health Canada. Special report on maternal mortality and severe morbidity in Canada—enhanced surveillance: the path to prevention. Cat. No. H39–4/44–2004E. Publication No. 5804. Ottawa: Minister of Public Works and Government Services Canada; 2004. Available at: http://www.phac-aspc.gc.ca/rhs-ssg/srmm-rsmm/pdf/ mat_mortality_e.pdf. Accessed August 8, 2011.

13. Lisonkova S, Liu S, Bartholomew S, Liston RM, Joseph KS. Temporal trends in maternal mortality in Canada II: estimates based on hospitalization data. J Obstet Gynaecol Can 2011;33(10):1020–30.

14. Hoyert DL. Maternal mortality and related concepts. National Center for Health Statistics. Vital Health Stat 2007;3(33). Available at: http://www.cdc.gov/nchs/data/series/sr_03/sr03_033.pdf. Accessed August 8, 2011.

15. Berg CJ, Callaghan WM, Syverson C, Henderson Z. Pregnancy-related mortality in the United States, 1998–2005. Obstet Gynecol 2010;116:1302–9.

16. Health Canada. Perinatal health indicators for Canada: a resource manual. Ottawa: Minister of Public Works and Government Services Canada; 2000.

17. Fair M. The development of national vital statistics in Canada: Part 1—from 1605 to 1945. Health Rep 1994;6:355–68.

18. Deneux-Tharaux C, Berg C, Bouvier-Colle MH, Gissler M, Harper M, Nannini A, et al. Underreporting of pregnancy-related mortality in the United States and Europe. Obstet Gynecol 2005;106:684–92.

19. Horon IL, Cheng D. Enhanced surveillance for pregnancy-associated mortality—Maryland, 1993–1998. JAMA 2001;285:1455–9.

20. Horon IL. Underreporting of maternal deaths on death certificates and the magnitude of the problem of maternal mortality. Am J Public Health 2005;95:478–82.

21. Turner LA, Cyr M, Kinch RA, Liston R, Kramer MS, Fair M, et al. Under-reporting of maternal mortality in Canada: a question of definition. Chronic Dis Can 2002;23:22–30.

22. Gissler M, Deneux-Tharaux C, Alexander S, Berg CJ, Bouvier-Colle MH, Harper M, et al. Pregnancy-related deaths in four regions of Europe and



the United States in 1999–2000: characterisation of unreported deaths. Eur J Obstet Gynecol Reprod Biol 2007;133:179–85.

23. Wilmoth J, Zureick S, Mizoguchi N, Inoue M, Oestergaard M. Levels and trends of maternal mortality in the world: the development of new estimates by the United Nations. Technical report. September 2010. Available at: http://www.who.int/reproductivehealth/publications/monitoring/MMR_technical_report.pdf. Accessed October 15, 2010.

24. Liu S, Joseph KS, Bartholomew S, Fahey J, Lee Lily, Allen AC, et al. Temporal trends and regional variations in severe maternal morbidity in Canada, 2003 to 2007. J Obstet Gynaecol Can 2010;32:847–55.

25. Wen SW, Liu S, Marcoux S, Fowler D. Uses and limitations of routine hospital admission/separation records for perinatal surveillance. Chronic Dis Can 1997;18:113–9.

26. Joseph KS, Fahey J. Validation of perinatal data in the Discharge Abstract Database of the Canadian Institute for Health Information. Chronic Dis Can 2009;29:96–100.

27. Dzakpasu S, Joseph KS, Huang L, Allen A, Sauve R, Young D. Decreasing diagnoses of birth asphyxia in Canada: fact or artifact. Pediatrics 2009;123:e668–e672.

28. Kramer MS, Rouleau J, Baskett TF, Joseph KS. Amniotic fluid embolism and medical induction of labour: a retrospective, population-based cohort study. Lancet 2006;368:1444–8.

29. Joseph KS, Liu S, Rouleau J, Kirby RS, Kramer MS, Sauve R, et al. Severe maternal morbidity in Canada, 2003 to 2007: surveillance using routine hospitalization data and ICD-10CA codes. J Obstet Gynaecol Can 2010;32:837–46.

Appendix. Underlying causes of maternal death: ICD-9 and ICD-10 classificationCategory ICD-9 code ICD-10 code

Ectopic and molar pregnancy 630–633 O00 .1, O00 .9

Other pregnancy with abortive outcome 634–639 O03 .5, O04 .6, O06 .6

Antepartum hemorrhage, abruptio placentae, and placenta previa

641 O44 .1, O45 .9, O46 .0

Hypertension complicating pregnancy, childbirth, and the puerperium

642 O10 .1, O13, O14 .1, O14 .9, O15 .0, O15 .9, O16

Other complications of pregnancy not otherwise specified

640, 643, 644, 645, 646 O26 .6, O26 .8, O95

Normal delivery and other indications for care in pregnancy, labour, and delivery*

650–659 O41 .1, O42 .9

Postpartum hemorrhage 666 O72 .0, O72 .1, O72 .3

Other complications occurring mainly in the course of labour and delivery not otherwise specified

660–665, 667–669 .3, 669 .5–669 .9 O62 .2, O69 .0, O71 .1

Major puerperal infection 670 O85, O86 .4, O86 .8

Venous complications in pregnancy and the puerperium

671 O22 .3, O22 .5, O22 .9

Obstetric embolism† 673 O88 .1, O88 .2

Other unspecified complications of the puerperium 674 .1–674 .4, 674 .6–694 .9 O90 .8

Diseases of circulatory system:

Diseases of the circulatory system complicating pregnancy, childbirth, and the puerperium

648 .5, 648 .6, 674 .0 O99 .4

Cardiac arrest, cardiac failure following Caesarean or other obstetric surgery or procedures including delivery not otherwise specified

669 .4 O75 .4

Cardiomyopathy in the puerperium 674 .8 O90 .3

Other indirect causes 647, 648 .0–648 .4, 648 .7–648 .9 O98 .4, O99 .1, O99 .2, O99 .3, O99 .8*Includes delivery of a completely normal case, multiple gestations, malposition and malpresentation of the fetus, disproportion, abnormality of organs and soft tissues of pelvis, known or suspected fetal abnormality affecting management of mother, other fetal and placental problems affecting management of mother, polyhydramnios, other problems associated with amniotic cavity and membranes, and other indications for care or intervention related to labour or delivery not otherwise specified .

†Includes thromboembolism and amniotic fluid embolism

NOTE: The ICD-10 codes listed above are diagnosis codes observed in maternal death records mapped to each category or set of ICD-9 codes and are not a complete listing of ICD-10 codes for each category .

temporal trends in maternal mortality in canada i: estimates based on vital statistics data

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