New York, Oct 13 (IANS): Pregnant women with high blood-sugar levels - even if it is below the cutoff for diabetes - are more likely to have babies with congenital heart defects, says a new study.

"We already knew that women with diabetes were at significantly increased risk for having children with congenital heart disease,” said the study's lead author James Priest, postdoctoral scholar in pediatric cardiology at Stanford University School of Medicine in California, US.

"What we now know, thanks to this new research, is that women who have elevated glucose values during pregnancy that don't meet our diagnostic criteria for diabetes also face an increased risk," Priest noted.

Pregnancy normally involves metabolic changes that make blood sugar -- glucose -- more available to the fetus than to the mother, an important adaptation for ensuring that the fetus gets enough nourishment.

However, in some women, especially those who are obese or who have a family history of diabetes, these changes progress too far, to the point that the mother develops gestational diabetes.

Although the risks of gestational diabetes have been well-studied, less attention has been paid to smaller metabolic changes in pregnancy.

In the new study, the researchers examined blood samples taken from 277 California women during the second trimester of pregnancy.

The control group comprised 180 women carrying infants without congenital heart disease.

The others had infants affected by serious heart defects.

The researchers found that average blood glucose levels were higher in women carrying fetuses with tetralogy of Fallot - the most common of the heart defects that cause blue baby syndrome, in which a baby is getting too little oxygen - than in women in the control group.

The study was published online in the journal JAMA Pediatrics.