Plaque buildup, an early sign of heart disease, was far more common in women who had given birth to four or more children than in those who had two or three, according to the research presented at the American College of Cardiology conference.
The survey did not say why this may be happening, and researchers did not consider whether stress could be a factor in the poorer health of these mothers.
However, researchers said the findings could help screening efforts and intervention strategies for women who have multiple children and who may not be aware that they face higher heart risks.
"Pregnancy is considered a monumental occasion in a woman's life, which is usually punctuated by the delivery of a child," said lead investigator Monika Sanghavi, chief cardiology fellow at the University of Texas Southwestern Medical Center.
"However, recently there is evidence that pregnancy might also function as a crystal ball, providing insight into a woman's future cardiovascular risk, and that the changes associated with pregnancy might have a longer term impact on a woman's health," she told reporters.
The study was the first of its kind to examine evidence of early plaque buildup in the heart that can eventually block blood flow and lead to stroke and heart attack. The study included more than 1,600 women in Texas. Their average age was 45, and 55 percent of them were African American.
The lowest rates of plaque buildup, or atherosclerosis, were seen in women who had two to three children -- or live births, which the study measured. The prevalence of subclinical atherosclerosis in women with two to three children was 11 percent. It was more than double that in women who had given birth four or more times, at 27 percent.
Researchers also found elevated rates -- 15 percent-- of hardening arteries in women who had never given birth, or who had only one child. Pregnancy causes a host of changes in the body -- such as more blood volume pumped through the heart, increased insulin resistance and higher cholesterol levels -- and researchers ant to explore if any of those could be contributing to poorer heart health in certain women.