These women were older, heavier, more likely to be smokers, and had diabetes.
They also had fewer years of education and increased cases of artificial insemination to help them conceive.
The study found that mothers of two or more children had higher levels of fat in their blood than before the first pregnancy compared with women who had one or no children at all.
According to the American Heart Association, the harmful levels of fat in the blood is one of the most important risk factors that can be controlled and may lead to heart disease and strokes.
"The study is interesting and raises many questions," said heart specialist Kitty Burlacher of the University of Pittsburgh Medical Center and director of the Women's Heart Program at Maggie-Wummens University Hospital. "But whenever they find it, it's just a link."
The association of factors that increase the risk of infertility does not mean that it is the cause, she said.
Women who have had one or no children may have done so voluntarily, so it is impossible to say so without talking to women, she said.