Doctors might be able to use current screening tests for gestational diabetes to identify women who are at risk for heart disease. (CBC)

Pregnant women with even mildly abnormal blood sugar test results may have an increased risk of heart disease later in life, a Canadian study suggests.

It's known that women with gestational diabetes — temporarily high blood sugar levels during pregnancy — have a higher risk of cardiovascular disease than the general population.

The study in Monday's issue of the Canadian Medical Association Journal shows the risk extends to women with mild glucose intolerance in pregnancy. It means doctors might be able to use current screening tests for gestational diabetes to identify women who are at risk for heart disease — the leading cause of death in Canadian women.

In the past, when doctors tested for gestational diabetes, women who didn't meet the threshold for diagnosis were told not to worry and nothing more was done. The new findings suggest that might be the right approach.

"We probably shouldn't be ignoring these mild abnormalities during pregnancy, as they may be a marker for women at increased heart disease risk who may benefit from extra surveillance and/or cardiovascular disease screening," study author Dr. Baiju Shah of the Institute for Clinical and Evaluative Sciences in Toronto said in an email.

The size of the effect was small, with the difference between "normal" and "mild" intolerance resulting in an extra five out of 10,000 women having a cardiovascular event such as hospitalization for a heart attack, coronary bypass or stroke over 12 years, Shah said.

Blood vessel changes

The researchers studied data on 435,696 women in Ontario who gave birth between April 1994 and March 1998 and were followed until March 31, 2008. Women with pre-existing diabetes were excluded.

As part of standard obstetric care, pregnant women in Ontario are screened for gestational diabetes with a glucose challenge screening test in the second trimester. She drinks a sweet liquid and then has blood drawn to evaluate how the body processes sugar. If the result is abnormal, women then have a diagnostic oral glucose tolerance test.

Since the women studied were mostly in their 30s, if the metabolic problems persist as they grow older then the differences might become more important for their cardiovascular risk, Shah said.

Under the "common soil" hypothesis, both Type 2 diabetes and cardiovascular disease have metabolic abnormalities like insulin resistance, obesity and cholesterol problems in common, so people with one of the diseases often develops the other.

The findings by Shah's team add weight to the hypothesis that Type 2 diabetes is a vascular disease first, Dr. J. Kennedy Cruickshank and Dr. Moulinath Baerjee of the department of cardiovascular sciences at the University of Manchester in England said in a journal commentary that accompanies the study.

"What the study by Retnakaran and Shah shows is that we all have a great deal to learn from subclinical blood vessel changes in younger women who are likely overweight during pregnancy."

The pair suggested that diabetes research should focus on the blood vessel rather than high blood sugar.