While it has been long known that diabetes in pregnancy raises the odds for congenital heart defects in babies.
The new findings reveal that risk extends even to women without diabetes in their earliest part of pregnancy, when the foetal heart is forming.
"Most women who have a child with congenital heart disease are not diabetic," said James Priest, assistant professor at the Stanford University in California.
The results showed that the risk of giving birth to a child with a congenital heart defect was elevated by 8 per cent for every increase of 10 milligrams per deciliter in blood glucose levels in the early stages of pregnancy.
"We found that in women who don't already have diabetes or develop diabetes during pregnancy, we can still measure risk for having a child with congenital heart disease by looking at their glucose values during the first trimester of pregnancy," Priest added.
For the study, published in The Journal of Paediatrics, the team examined medical records from 19,107 pairs of mothers and their babies born between 2009 and 2015, which included details of the mothers' prenatal care, including blood test results and any cardiac diagnoses made for the babies during pregnancy or after birth.
The study may be helpful to measure blood glucose early in pregnancy in all pregnant women to help determine which individuals are at greater risk for having a baby with a heart defect.
"Knowing about defects prenatally improves outcomes because mothers can receive specialised care that increases their babies' chances of being healthier after birth," Priest added.