Pregnant women with mild glucose intolerance have a significantly increased—though still small—risk of developing cardiovascular disease later on, an analysis of data on 435,696 Canadian women suggested.
Compared with pregnant women who were thought to have normal glucose tolerance, the risk for developing cardiovascular disease during a median of 12 years after pregnancy increased by 19% in women with presumed hyperglycemia but not gestational diabetes, and by 66% in women with gestational diabetes, reported Dr. Ravi Retnakaran and Dr. Baiju R. Shah, both of the University of Toronto.
The absolute risk for cardiovascular disease increased by 0.05% to an absolute rate of 2.3/10,000 person-years in women with presumed hyperglycemia but not gestational diabetes, and by 0.16% to an absolute rate of 4.2/10,000 person-years in women with gestational diabetes, compared with a rate of 1.9/10,000 person-years in women presumed to have normal glucose tolerance.
The study was published online in the Canadian Medical Association Journal (2009 [doi:10.1503/cmaj.090569
The population-based cohort study followed women with no history of pregestational diabetes who gave birth between April 1994 and March 1998. The investigators did not have access to laboratory glucose values, but used the Canadian Health System's administrative database to identify three groups of pregnant women.
A “normal” group of 349,977 women had an oral glucose challenge test but received no further testing, suggesting normal results. A mild glucose intolerance group of 71,831 women had two glucose tests on the same day, and so presumably had hyperglycemia on the glucose challenge followed by a glucose tolerance test, but were excluded from having gestational diabetes based on an algorithm analogous to one used by the Ontario Diabetes Database. The third group of 13,888 women had both tests and were thought to have gestational diabetes based on the algorithm.
The analyses adjusted for the effects of age, year of delivery, location of residence (rural vs. urban), income, comorbidity, preexisting hypertension, and gestational hypertension.
Previous studies have shown that gestational diabetes is associated with an increased risk of later cardiovascular disease. This study raises the possibility that hyperglycemia without gestational diabetes also may be associated with subsequent cardiovascular disease, the authors noted.
When the results were adjusted for the later development of diabetes, the mild gestational hyperglycemia no longer was significantly associated with an increased risk for cardiovascular disease. Given the low underlying cardiovascular risk of this young cohort and the long time generally needed to develop macrovascular disease in patients with type 2 diabetes, however, it seems most likely that vascular disease develops in parallel with diabetes instead of necessarily following it, they added.
In an editorial, Dr. J. Kennedy Cruickshank and Dr. Moulinath Banerjee, both of the University of Manchester (England), said that the findings add weight to the “common soil” hypothesis that vessel damage and hyperglycemia have a common cause (CMAJ 2009 [doi:10.1503/cmaj.091396
Perhaps type 2 diabetes no longer can be defined as “just” hyperglycemia, and the definition should include earlier blood vessel damage in addition to or instead of glycemia, they suggested. That might help explain what they called the failure of intensive glycemic control regimens to reduce mortality or improve cardiovascular event rates.
Dr. Cruickshank and Dr. Banerjee suggested that diabetes research focused on insulin resistance may have been misdirected, and that the next generation of diabetes treatments should focus on the blood vessel.
All of the physicians mentioned in this article declared having no conflicts of interest related to these topics.