Stillbirth epidemiology, diabetes, and other risk factors among all pregnancies in Alberta from 2000 to 2009
Stillbirth epidemiology, diabetes, and other risk factors among all
pregnancies in Alberta from 2000 to 2009
Richard T. Oster and Ellen L. Toth
Despite the first comprehensive set of worldwide estimates suggesting
that 2.6 million stillbirths occurred in 2009 (1), previously stillbirths have
been given little recognition compared to other pregnancy complications
or causes of maternal and neonatal deaths. The tragedy and impact of
stillbirth is however receiving new warranted attention clinically and
academically, as highlighted in a recent special series of the Lancet (2).
In Canada, women of First Nations descent have been shown to be at an
elevated risk of numerous adverse pregnancy outcomes, including
stillbirths which are 68% more likely among pregnant First Nations
women according to a systematic review and meta-analysis (3). This has
sparked new research into stillbirth rates and risk factors among First
Nations women, with Auger et al (4) pointing toward diabetes (driven by
obesity) as a major cause. However, the epidemiology of First Nations
stillbirths is still poorly understood as stillbirth type (antepartum or
intrapartum) has not been considered, longitudinal changes have not
been rigorously explored, and data on risk factors (including diabetes in
pregnancy type) is limited.
The purpose of this study was to gain a better understanding of extent of
the problem of stillbirths and the relationship between stillbirth and other
potential pregnancy-related factors may yield knowledge to better inform
intervention type and timing, with the goal of lowering risk of stillbirth in
First Nations pregnancies. We used provincial administrative data to: 1)
determine and compare the age-adjusted annual prevalence rates of
stillbirth longitudinally by First Nations and non-First Nations ethnicity;
and 2) examine the relationship between pre-existing diabetes and
gestational diabetes mellitus (GDM), stillbirths, and other possible
underlying factors amongst First Nations and non-First Nations
Department of Medicine, University of Alberta
(antepartum and intrapartum) for the entire province by ethnicity were
calculated and compared. Rates were age-standardized to the maternal age
distribution of the total number of pregnancies in 2005 from the Canadian Vital
Statistics by the direct method. Crude prevalence rates were also calculated to
make comparisons with previous studies. For longitudinal analyses, the
Average Annual Percent Change (AAPC) in stillbirth prevalence over time was
computed and compared between ethnicities. Tests of parallelism were
performed to determine if trends over time differed by ethnicity. Statistical
modeling (purposeful) using logistic regression was used to evaluate the
relationships between stillbirth (antepartum and intrapartum), diabetes in
pregnancy, and other potential explanatory variables.
Between 2000-2009 there were 433,445 pregnancies in Alberta. Only records
with gestational age ≥ 20 weeks were included in the analysis. Records with
missing stillbirth data were not included. A total 426,945 pregnancy records
were explored, of which 28,296 (6.63%) were First Nations women.
The overall age-adjusted rates of antepartum and intrapartum stillbirth were
significantly (p < 0.05) higher in the First Nations group (1.30% and 0.39%
respectively) compared to non-First Nations (0.46% and 0.22% respectively).
The rate ratios (First Nations to non-First Nations) for age-adjusted antepartum
and intrapartum stillbirth prevalence were and 2.86 and 1.80 respectively.
P-value for Comparison
In multivariate analysis, First Nations ethnicity was an independent predictor of
antepartum stillbirth (OR 1.70, 95% CI 1.47-1.97) and intrapartum stillbirth (OR
1.62, 95% CI 1.29-2.03) (Table 2). Age ≥ 35, history of abortion, history of
stillbirth, and pregestational diabetes were significant risk factors for both
antepartum and intrapartum stillbirth regardless of ethnicity. Gestational
diabetes was not a risk factor for stillbirths.
Table 2. Multivariate predictors of antepartum and intrapartum stillbirth among Albertan women by ethnicity.
Values are ORs (95% CI).
(n = 426 945)
First Nations women
(n = 28 296)
OR for antepartum OR for intrapartum OR for antepartum OR for intrapartum
Parity (≤ 3)†
Pregestational weight ≥
History of C-section
Stillbirth rates have remained stable in Alberta over 10 years, but are higher in
First Nations pregnancies compared to non-First Nations. This may be at least
in-part due to the higher incidence and prevalence of type 2 diabetes amongst
young First Nations women. Increased awareness of pregestational diabetes
could lead to better recognition and management and decreased numbers of
History of LGA
History of fetal anomaly
History of stillbirth
History of neonatal death
Figure 1. Age-adjusted prevalence of stillbirth over time in Alberta by ethnicity. A = antepartum stillbirth ; B =
Age ≥ 35
History of abortion
All analyses were conducted using STATA statistical software (version 11)
and Joinpoint (version 3.5.1). Annual age-adjusted rates of stillbirth
Between 2000 and 2009, age-adjusted prevalence rates of both antepartum
and intrapartum stillbirth remained stable in both groups (Figure 1, Figure 2,
Table 1). No longitudinal between group differences (parallelism) were noted.
Ethical approval was obtained from the Human Research Ethics Board of
the University of Alberta. We conducted a secondary analysis of data
previously obtained (5). Briefly, anonymized data from all provincial
delivery records for the years 2000-2009 was requested from the Alberta
Perinatal Health Program, which compiles perinatal data from hospital
births and registered midwife attended home births. Specifics on how the
APHP collects and characterizes data can be found elsewhere (5).
Importantly, prior to our acquisition, the data was sent to Alberta Health
for First Nations ethnicity ascertainment. Three unique and distinct
populations of Canadian Aboriginal people are recognized by the federal
government: First Nations, Métis (mixed blood) and Inuit. De-identified
complete data was returned by AHW in STATA format. The data were
matched using the Personal Health Number and First Nations individuals
were classified as any Alberta resident registered under the Indian Act of
Canada and entitled to Treaty status with the federal Government.
Women delivering in Alberta with a First Nations identifier (First Nations
or Inuit) were considered “First Nations” whereas all other women
(including First Nations individuals without Treaty status and Métis
individuals) were considered “non-First Nations”.
Table 1. Ethnicity comparisons of antepartum and intrapartume stillbirth prevalence over time in Alberta,
2000-2009. Values are AAPC (95% CI) in age-adjusted rates.
1. Cousens S et al. The Lancet. 2011;377(9774):1319-30.
2. The Lancet. 2011;377 (9774).
3. Shah PS et al. Women’s Health Issues. 2011;21(1):28-39.
4. Auger N et al. Canadian Medical Association Journal. 2013. Epub.
5. Oster RT. Dissertation. University of Alberta. 2013