Impact of pre-pregnancy diabetes mellitus on congenital anomalies, Canada, 2002-2012 - HPCDP: Volume 35-5, July 2015

Volume 35 · Number 5 · July 2015

Abstract

Objective: To examine the impact of pre-pregnancy diabetes mellitus (DM) on the population birth prevalence of congenital anomalies in Canada.

Methods: We carried out a population-based study of all women who delivered in Canadian hospitals (except those in the province of Quebec) between April 2002 and March 2013 and their live-born infants with a birth weight of 500 grams or more and/or a gestational age of 22 weeks or more. Pre-pregnancy type 1 or type 2 DM was identified using ICD-10 diagnostic codes. The association between DM and all congenital anomalies as well as specific congenital anomaly categories was estimated using adjusted odds ratios; the impact was calculated as a population attributable risk percent (PAR%).

Results: There were 118 892 infants with a congenital anomaly among 2 839 680 live births (41.9 per 1000). While the prevalence of any congenital anomaly declined from 50.7 per 1000 live births in 2002/03 to 41.5 per 1000 in 2012/13, the corresponding PAR% for a congenital anomaly related to pre-pregnancy DM rose from 0.6% (95% confidence interval [CI]: 0.4-0.8) to 1.2% (95% CI: 0.9-1.4). Specifically, the PAR% for congenital cardiovascular defects increased from 2.3% (95% CI: 1.7-2.9) to 4.2% (95% CI: 3.5-4.9) and for gastrointestinal defects from 0.8% (95% CI: 0.2-1.9) to 1.4% (95% CI: 0.7-2.6) over the study period.

Conclusion: Although there has been a relative decline in the prevalence of congenital anomalies in Canada, the proportion of congenital anomalies due to maternal pre-pregnancy DM has increased. Enhancement of preconception care initiatives for women with DM is recommended.

Keywords: diabetes mellitus, pre-pregnancy, congenital anomaly, birth defect, trends, population attributable risk percent.

A total of 118 892 infants with one or more congenital anomalies were identified among the 2 839 680 infants born during the study period-equivalent to 41.9 congenital anomalies per 1000 live births. The prevalence of any congenital anomalies declined from 50.7 per 1000 live births in 2002/03 to 38.5 per 1000 in 2007/08, then rose to 41.5 per 1000 in 2012/13. The prevalence of most of the major congenital anomaly categories, for instance, musculoskeletal defects and cardiovascular defects, declined over this entire period while genitourinary defects increased (Figure 2).

The rate of any congenital anomaly was 93.4 per 1000 live births among women with pre-pregnancy DM versus 41.5 per 1000 live births among women without pre-pregnancy DM. Rates were similar among women with type 1 DM (93.7 per 1000 live births) and type 2 DM (93.3 per 1000 live births). The adjusted OR for congenital anomalies associated with type 1 DM in the entire population was 2.38 (95% CI: 2.20-2.57), while that associated with type 2 DM was 2.31 (95% CI: 2.16-2.47). The magnitude of the association between type 1 and type 2 DM and major categories of congenital anomalies was similar except for musculoskeletal anomalies, which were not associated with type 1 DM (Table 1).

Overall, 0.9% of cases of congenital anomalies in the population were attributable to pre-pregnancy DM (Table 1). The etiological contribution of pre-pregnancy DM to congenital anomalies increased between 2002/03 and 2012/13: the annual PAR% for congenital anomalies related to pre-pregnancy DM doubled over time, from 0.6% (95% CI: 0.4-0.8) in 2002/03 to 1.2% (95% CI: 0.9-1.4) in 2012/13 (Figure 3), because the prevalence of maternal pre-pregnancy DM increased from 4.6 per 1000 live births in 2002/03 to 7.5 per 1000 live births in 2012/13 while the relation between pre-pregnancy DM and congenital anomalies remained unchanged (the adjusted OR was 2.20 [95% CI: 1.77-2.74] in 2002/03 and 2.55 [95% CI: 2.21-2.94] in 2012/13; p >.05 for the difference in adjusted ORs).

Rates of congenital cardiovascular defects were 5 times higher and rates of central nervous system anomalies were 3 times higher among women with pre-pregnancy DM compared with those without pre-pregnancy DM. In particular, approximately 3% of cardiovascular defects in infants could be attributed to maternal pre-pregnancy DM (Table 1). The corresponding PAR% increased over time for cardiovascular defects, from 2.3% (95% CI: 1.7-2.9) to 4.2% (95% CI: 3.5-4.9) and for gastrointestinal defects, from 0.8% (95% CI: 0.2-1.9) to 1.4% (95% CI: 0.7-2.6), as well as for genitourinary and musculoskeletal defects (Figure 4).

Discussion

The birth prevalence of congenital anomalies in Canada was approximately 42 per 1000 live births from 2002/03 to 2012/13, and several specific congenital anomalies declined over the study period. However, exposure of fetuses to maternal pre-pregnancy DM increased over this 11-year period, resulting in an increase in the contribution of pre-pregnancy DM to the occurrence of congenital anomalies. Although the etiology of congenital anomalies is multifactorial and largely unknown,^{Footnote 1 Footnote 4 Footnote 20} several non-inherited factors play a significant role in their development, including maternal age, pre-pregnancy DM, obesity and folate insufficiency.^{Footnote 1 Footnote 4 Footnote 6 Footnote 21-23} The current analysis of recent Canadian data suggests that pre-pregnancy DM remains a significant and modifiable risk factor.

Maternal DM has been shown to increase the risk of congenital anomalies by 2 to 5 times that of women without diabetes.^{Footnote 7-11} Prevalence of pre-pregnancy diabetes in Ontario doubled between 1996 and 2010 among women aged 30 years and older,^{Footnote 12} likely because of more sedentary lifestyles and higher rates of obesity. Between 2000 and 2010, the prevalence of DM in the entire Canadian population increased by 103% and is currently at 7.6%; increases were especially evident among those aged 35 to 44 years.^{Footnote 23} Moreover, it is estimated that approximately 20% of DM cases are undiagnosed.^{Footnote 24} The current high prevalence of both pre-pregnancy DM and overweight/obesity^{Footnote 25} are of concern since both are significantly associated with an elevated risk of congenital anomalies.^{Footnote 25 Footnote 26} Specifically, fetuses of obese mothers are more likely to be affected by neural tube defects or cardiovascular anomalies compared with fetuses of mothers with a normal BMI.^{Footnote 25}

The association between pre-pregnancy DM and congenital anomalies we observed was consistent with other studies.^{Footnote 5-11} For instance, Nielsen et al.^{Footnote 5} found a prevalence odds ratio of congenital abnormalities in infants of women with diabetes of 2.1 (95% CI: 1.5-3.1) and particularly strong associations for renal agenesis, obstructive abnormalities of the urinary tract, cardiovascular congenital abnormalities and multiple congenital abnormalities.

Periconceptional glycemic control can help mitigate the risk of congenital anomalies in women with DM.^{Footnote 4 Footnote 8 Footnote 12 Footnote 27} In a meta-analysis of observational studies of periconceptional glycemic control, the risk of congenital malformation increased with each standard deviation unit increase in maternal glycosylated hemoglobin concentration by an OR of 1.2 (95% CI: 1.1-1.4).^{Footnote 27} Studies show that preconception care is associated with a lower glycosylated hemoglobin concentration and a significantly lower risk of congenital anomalies among women with pre-pregnancy DM.^{Footnote 13} Thus, strategies should be developed to inform women with known DM on the importance of effective preconception and prenatal health care, especially in regards to monitoring and managing blood glucose, blood pressure and target organ complications, such as retinal or renal damage. ^{Footnote 13 Footnote 14 Footnote 28 Footnote 29}

Strengths and limitations

Our study had several limitations. First, the decline in prevalence of congenital anomalies over time is, in part, as result of increased availability of prenatal diagnosis and pregnancy termination for serious congenital anomalies. However, our data source did not have direct information about either prenatal screening or prenatal care practices, and so we were unable to exclude such effects. Since the mid-1990s, improved prenatal detection of congenital anomalies may have led to higher rates of pregnancy termination of fetuses with serious congenital anomalies, thereby leading to a decline in the proportion of live-born infants with a congenital anomaly.^{Footnote 2 Footnote 30 Footnote 31}

Second, our mother-newborn linked dataset was limited to live births; late pregnancy terminations and spontaneous stillbirths were not accounted for. Although how the inclusion of stillbirths would alter the association between DM and congenital anomalies is unclear, it is likely that this exclusion resulted in underestimates of the association between maternal DM (especially type 1 DM) and the more severe congenital anomalies caused by this condition. Further, congenital anomalies were determined within 30 days of birth, so anomalies detected in subsequent hospital readmissions were not accounted for. This may have led to underestimates of the association between maternal DM and minor congenital anomalies or those congenital anomalies that present later in infancy.

Third, no information on maternal or paternal risk factors for congenital anomalies, other than maternal age and DM, was available in the DAD. However, lack of such information would not have impacted the temporal trends in congenital anomalies examined in this study. In terms of changes in the rate of central nervous system defects-largely comprising neural tube defects-fortification of flour with folic acid has been mandatory in Canada since 1998, and the decline in numbers of neural tube defects plateaued before the start of the study period.^{Footnote 32 Footnote 33} Further, the slight increase in congenital anomalies after 2007/08 in Canada is concordant with the increase in pre-pregnancy DM and maternal age (Figure 1 and Figure 2). Enhanced data collection among a large cohort of women with pre-pregnancy DM, with detailed ascertainment of risk factors, such as maternal obesity, would address some of the deficiencies in our study.^{Footnote 1 Footnote 31} Finally, diagnosis of congenital anomalies is typically made with knowledge of maternal DM and this may have led to an ascertainment bias, especially with regard to minor congenital anomalies.

In summary, although there has been a relative decline in the birth prevalence of congenital anomalies in Canada, a larger proportion of congenital anomalies can now be attributed to maternal pre-pregnancy DM compared with previous years. Our findings reinforce the importance of preconception care programs, particularly among women with DM, as well as of early screening in pregnancy to detect structural anomalies to guide their management. Strategies that address and prevent the occurrence of DM among women of reproductive age are also important for preventing congenital anomalies due to pre-pregnancy DM.

Acknowledgements

This study was carried out under the auspices of the Canadian Perinatal Surveillance System of the Public Health Agency of Canada. We thank the Canadian Institute for Health Information for providing access to the Discharge Abstract Database (DAD). We thank Susie Dzakpasu (Public Health Agency of Canada), Jane Evans (University of Manitoba), Michael S. Kramer (McGill University), Wei Luo, Chantal Nelson and Victoria Otterrman (all with the Public Health Agency of Canada) for comments on an earlier version of this this study. KSJ and JGR are supported by Applied Chairs awarded by the Canadian Institutes of Health Research.

References