Our large sample size over a 10-year period allowed for analyses that indicated that having diabetes in pregnancy (particularly pre-existing diabetes) compounds already increased risks of adverse pregnancy outcomes for First Nations women. The results of our study are unique in that they are the first results that describe large-scale trends over time for both pre-existing diabetes and GDM in a First Nations population. Although GDM prevalence was disproportionately higher among First Nations women, we found that prevalence is growing more rapidly among non-First Nations women. First Nations women also suffer a greater than 2-fold higher prevalence of pre-existing diabetes, which is likely contributed to by early onset of type 2 diabetes in the prime child-bearing years (i.e., twenties and thirties) [6]. However, the prevalence of pre-existing diabetes in pregnancy was generally stable over time amongst both groups. An additional novel finding was that the epidemiological profile of diabetes in pregnancy in Alberta does not appear to be as severe in comparison with other provinces. Our study also provides new information about previously unexplored maternal characteristics and antenatal risk factors, and their associations with diabetes in pregnancy.
This study is the first to calculate age-adjusted GDM and pre-existing diabetes prevalence among a First Nations population. Because advancing maternal age is a risk factor for GDM, and the First Nations population consists mostly of younger age groups [3, 18], the results presented in previous reports may underestimate the differences between First Nations and general populations. Being of First Nations descent was independently associated with both GDM and pre-existing diabetes in pregnancy. Finally, in addition to risk factors identified in previous studies [19–21], the results of this study indicate that previous stillbirth, previous cesarean section, previous abortion (spontaneous or therapeutic), previous LGA infant, and the presence of proteinuria are also independently associated with GDM and pre-existing diabetes in pregnancy in Indigenous women.
Values for several components of the total antepartum risk score are higher in other First Nations populations. These components include previous preterm birth [22], smoking during pregnancy [23], fetal exposure to illicit drugs [24], and stillbirth [25]. In the current study, pregnancy risk factors that showed the highest disparity between First Nations and non-First Nations women included smoking anytime during pregnancy (3.2-fold), the presence of anemia (3.8-fold), alcohol consumption any time during pregnancy (6.1-fold), and drug dependency (7.3-fold). It is likely that these factors contribute to the observed poorer outcomes among First Nations infants, and interventions are clearly required to mitigate these risks. The ethnic inequalities persisted in women who only had diabetes in pregnancy. To our knowledge, this was the first study to find adverse effects by First Nations status among women with diabetes, associated with high pre-existing weight, pre-existing hypertension, proteinuria, anemia, stillbirth, smoking, alcohol consumption, and drug dependency. All of these factors were significantly more common among First Nations women. This study is also the first to compare risk factors and pregnancy outcomes by diabetes status among First Nations women only. Having diabetes (especially pre-existing) clearly increased the risk of several adverse pregnancy risk factors and outcomes, similar to previously reported results for non-Indigenous women [26].
This study confirmed the results of previous studies that found a higher prevalence of GDM among First Nations women [9, 19, 20, 27]. However, the epidemiological profile in Alberta did not seem to be as severe as in other provinces. The crude First Nations GDM prevalence in Alberta (4.3%) was lower compared with First Nations populations in other parts of Canada, such as Manitoba (6.9%), Quebec (8.5%), and northwestern Ontario (8.4%) [20, 21, 27]. The First Nations to non-First Nations crude rate ratio of 1.1 for GDM prevalence was also lower in Alberta compared with the 1.8 and 2.9 ratios reported for women in the provinces of Saskatchewan and Manitoba, respectively [19, 20]. Similarly, we have recently found that rate ratios for overall diabetes incidence and prevalence are also lower in Alberta compared with other provinces [7]. The results of our study cannot explain provincial differences, but we speculate they may be related to socio-economic differences, and/or a combination of provincial and community-based programming targeting awareness such as the provincial Alberta Diabetes Strategy, the federally funded Aboriginal Diabetes Initiative, or changes in clinical practice. Future studies are needed to uncover reasons for regional variations, and should include age-adjustments for more informative comparisons across ethnic groups.
GDM prevalence is increasing in many populations worldwide [28], and this pattern is also present among non-First Nations Albertan women. The increasing age of pregnant non-First Nations women and an influx of minority immigrants likely have contributed to this increase in prevalence [20, 29]. The situation does not seem as clear among Indigenous populations, because prevalence is not increasing significantly in Alberta First Nations women. This is consistent with our article on overall diabetes prevalence in Alberta [7], which reported that overall diabetes prevalence is increasing more rapidly among the non-First Nations population. One US study found that GDM prevalence among American Indian women increased from 3.1% to 4.1% during 1989–2000 [30]. However, studies among Aborigines in Australia have found that prevalence values are stable or even decreasing over time [31, 32].
Liu et al [33] reported a higher pre-existing diabetes prevalence in Ontario First Nations women (3.9%) compared with their non-First Nations counterparts (1.8%). This result is consistent with our results and with the increased numbers of young women of child-bearing age with type 2 diabetes that we and others have documented in First Nations populations [6, 7]. As with GDM, pre-existing diabetes prevalence is lower among Alberta First Nations (1.0% crude) compared with Ontario First Nations women.
To our knowledge, this study is the first to describe trends in pre-existing diabetes in pregnancy over time in an Indigenous population. The stability of prevalence in the First Nations and non-First Nations populations is surprising and encouraging, because the prevalence of pre-existing diabetes in pregnancy is increasing worldwide [34] and overall diabetes prevalence appears to be increasing in both the First Nations and non-First Nations populations [7].
There were several limitations of this study. The results cannot be generalized to non-registered First Nations individuals or to Métis individuals. These individuals could not be identified and were included in the non-First Nations population group. Also, the completeness of coverage of the First Nations identification could not be determined, so the observed ethnic (First Nations vs. non-First Nations) disparities could have been underestimated. Screening for diabetes in early pregnancy is often not performed (personal observation, E.L.T.) even though it is recommended for women with multiple risk factors [13]. Therefore, it is also likely that some First Nations women with pre-existing diabetes were not diagnosed, and were later classified as having GDM. This error would underestimate the magnitude of the findings of worse outcomes with pre-existing diabetes than with GDM. Whether the recorded pre-existing diabetes cases were type 1 or type 2 diabetes could not be discerned from the administrative data. Clinical experience suggests that most diabetes in young First Nations women is type 2 diabetes, but the prevalence of type 2 diabetes amongst non-First Nations populations (as we defined them) is also increasing. We believe that this change is due to obesity, immigration, and the inclusion of non-registered Indigenous persons. Further research is needed to determine the specific contributions of type 1 and type 2 diabetes, but glucose control is equally important to perinatal outcomes regardless the type of pre-existing diabetes. The degree to which diabetes was successfully managed (glucose control, hemoglobin A1c) also could not be determined for the study population. Finally, the contribution of other potential contextual predictors (e.g., healthcare access, lifestyle, overweight/obesity, social environment, income) to the logistic regression models could not be assessed.