Single-child mothers who develop high blood pressure during pregnancy may be more likely to die from heart disease later in life.

Researchers looked at data from more than 800,000 Norwegian mothers. Overall women with preeclampsia during their first pregnancy had a higher risk of heart-disease-related death. The risk skyrocketed to nine times higher among women who had only one child and was nearly two and half times for women who had more than one child.

This is the first time that increased risk among single-child mothers has been reported and suggests these women require special monitoring.

The findings appear online in "British Medical Journal".