Women who have four or more children are much more likely to have evidence of plaque in their heart or thickening of their arteries - early signs of cardiovascular disease. (Agencies)
Researchers at the University of Texas Southwestern Medical Center set out to determine whether the number of live births is associated with early signs of heart disease.
"This is not a recommendation for women to only have two or three children," said Monika Sanghavi, Chief Cardiology fellow, University of Texas Southwestern Medical Center, and lead investigator of the study.
The study was the first to look at two markers of subclinical atherosclerosis - a gradual narrowing and hardening of the arteries that can eventually block blood flow and lead to stroke and heart attack.
The study included 1,644 women from the Dallas Heart Study, a multiethnic population-based cohort, who had both self-reported information about the number of live births and relevant imaging study data available.
The average age at the time of analysis was 45 years and slightly more than half of the women (55 per cent) were African-American.
Coronary artery calcium (CAC) scores were measured using computed tomography imaging and aortic wall thickness (AWT) by magnetic resonance imaging to determine whether or not women had evidence of subclinical atherosclerosis in the heart and artery walls.
CAC was positive if it was greater than 10 and AWT was abnormal if it was greater than the 75th percentile for age and gender.
Using women who had two or three live births as a reference, women who had given birth to four or more children had an approximately two-fold increased risk of having abnormal CAC or AWT.
Surprisingly, women who had zero or just one live birth were also more likely to show evidence of subclinical atherosclerosis - revealing a U-shaped relationship.
Sanghavi and colleagues speculated they may have captured some women in this group who have an underlying condition that prevents them from carrying a first or second pregnancy to term, which may also predispose them to cardiovascular disease or risk factors.
Pregnancy itself sparks a cascade of changes that can place more strain on a woman's cardiovascular system. For example, the volume of blood being pumped through the heart increases by 50 per cent.
In addition, other physiological and metabolic changes occur (eg, increased insulin resistance and higher cholesterol levels), researchers said.
The research will be presented at a meeting of the American College of Cardiology.
Women who have four or more children are much more likely to have evidence of plaque in their heart or thickening of their arteries - early signs of cardiovascular disease.