Women who have given birth to several children may have a faster rate of plaque build-up in the neck arteries than those with fewer or no children, hints a new study.

The significance of the finding - including whether it translates into a greater long-term risk of stroke - is not clear.

But some past studies have found that the more children a woman has, the higher her risk of heart disease or stroke later on. And that relationship appears to be only partly explained by factors such as weight gain and lifestyle habits.

These latest findings, reported in the journal Stroke, suggest there may be something about pregnancy itself that contributes to progression in the intima-media thickness, or IMT, of the carotid arteries in the neck. An increase in IMT over time serves as a marker of plaque buildup in the arteries.

“We think that some of the many biological changes that accompany pregnancy may be involved,” lead researcher Dr. Michael R. Skilton, of the Baker IDI Heart & Diabetes Institute in Melbourne, Australia, told Reuters Health in an email.

For example, he said, blood cholesterol levels go up during pregnancy, as does resistance to the hormone insulin - which, outside of pregnancy, is a precursor to type 2 diabetes. Pregnancy also alters levels of sex hormones, including estrogen and testosterone, and creates a state of inflammation in the body.

Some or all of those changes may contribute to a concurrent increase in carotid IMT, according to Skilton and his colleagues.

However, the researchers say further studies are needed before women’s pregnancy history can be considered a factor in the risk of stroke or heart disease.

According to Skilton, all women should still focus on maintaining a healthy lifestyle - a well-balanced diet, regular exercise, not smoking - and controlling any of the traditional risk factors for heart disease and stroke that they may have. Some of those include high blood pressure, High cholesterol, obesity and diabetes.

For the study, Skilton and his colleagues used data from an ongoing project that began following a group of Finnish children and teenagers in 1980. That larger study is aimed at identifying risk factors for cardiovascular disease that take shape early in life.

Skilton’s team focused on 1,800 study participants who had ultrasound scans of their carotid arteries in 2001 and 2007, when the group ranged in age from their 20s through mid-40s.

The researchers looked at whether there was any relationship between the number of children women had in the six-year gap between ultrasounds and the progression in carotid IMT.

Overall, the study found, the average carotid IMT increased in both women and men over the study period - by an average of roughly 7 micrometers per year for women, and 9 micrometers for men.

Similarly, for every child a woman had during the six-year period, her IMT progression increased by 7.5 micrometers.

So the IMT increase associated with childbirth is on par with what’s seen over one year of “normal aging,” Skilton said.

The number of children women had was related to certain changes in traditional cardiovascular risk factors over the study period. Women who’d had two or more children tended to put on more abdominal fat than other women, and as a group they showed a dip in levels of “good” HDL cholesterol.

However, those changes did not fully explain the connection between pregnancy and carotid IMT progression.

Future studies should try to undercover the mechanisms that underlie the relationship, according to Skilton.

“Once we have identified the mechanism via which pregnancy can influence the health of the blood vessels,” he said, “we would like to see whether or not we can find prevention strategies that are suitable for use during pregnancy that could reduce the risks.”

SOURCE: Stroke, online June 10, 2010.