Higher number of live births associated with poorer cardiovascular health

Reviewed by James Ives, M.Psych. (Editor)Nov 4 2019

Using medical record and survey data collected from more than 3,400 women, Johns Hopkins Medicine researchers have added to evidence that women who have given birth five or more times were more likely than those who had fewer births to have more risk factors for heart disease, including obesity, high blood pressure and inadequate physical activity.

The researchers say that their findings, published in the December 2019 issue of the American Journal of Obstetrics and Gynecology, don't suggest that women should have fewer children, but rather that physicians, partners and mothers pay more attention to postpartum wellness and risk factor screening, particularly among those with larger numbers of births.

In addition, the new study does not suggest a cause and effect relationship between pregnancy itself and heart disease. "Both biological and social factors are likely the culprits in raising heart disease risk," says Erin D. Michos, M.D., M.H.S., associate professor of medicine at the Johns Hopkins University School of Medicine, and director of the women's cardiovascular health program at the Ciccarone Center for Prevention of Cardiovascular Disease. She says that women with more children may have less time to exercise or prepare healthy meals, or may focus on taking care of their children at the expense of their own health.

Also, women gain weight during pregnancy. This raises blood fats and increases resistance to insulina hormone that controls blood sugar levels, which may all play a role in increasing heart disease risk. Women with multiple pregnancies may find it harder to get back to their pre-pregnancy weight after each pregnancy, and this weight gain during their childbearing years often stays with them into later life.

The good news, the investigators say, is that many risk factors for heart disease can be reduced through lifestyle or medical interventions.

Pregnancy is a critical time with so much focus on the baby that we need to make sure we aren't neglecting mothers. We want to emphasize that postpartum plans should include customized strategies to help mothers maintain their heart health."

Erin D. Michos, associate professor of medicine, Johns Hopkins University School of Medicine

Heart disease remains the number one cause of death for women in the U.S., according to the National Institutes of Health.

According to Michos, other studies from institutions in the U.S. and elsewhere have shown links between number of live births and increased cardiovascular disease risk. A large analysis, combining the results from 10 studies and over 3 million women, found that there was a dose-response relationship between higher number of pregnancies and cardiovascular disease risk. However, some other studies didn't find this relationship. The current study focused on achievement of ideal cardiovascular health, by examining specific modifiable factors of cardiovascular disease, instead of looking at incidents of heart disease and stroke.

For the study, Michos and her team used survey and medical record data from the U.S. government-funded Multi-Ethnic Study of Atherosclerosis. Between 2000 and 2002, the government's study organizers recruited 3,430 women between 45 and 84 years old in the U.S., who underwent a physical exam, gave blood samples and completed surveys about their health habits. Thirty-eight percent were white, 28% were African American, 23% were Hispanic and 11% were Chinese American. Each participant reported their number of live births, which included Caesarean section births. Some 18% of women reported no births, 39% had one or two, 19% had three or four, and 13% had five or more births.

The Johns Hopkins researchers sifted through the study participants' recorded data and assigned a heart health score between 0 and 2 for each of seven well-established risk factors, including smoking, physical activity, body mass index (BMI), diet of heart-healthy foods, blood pressure, total cholesterol and blood sugar. A score of 0 correlated with a poorer measurement for each risk factor, 1 was associated with an intermediate level and 2 was the best performance for each factor. Then, the scientists added all seven scores for each patient to come up with a total heart health score.

The 698 women who scored 11–14 total points for all seven factors had the best cardiovascular health scores of the group and were considered to be in optimal cardiovascular health. There were 1,118 people who scored 9–10 points, and they were considered at average risk. Finally, 1,614 women with 8 or fewer total points were considered to have "inadequate" heart health scores. Cardiovascular health scores were lower on average for women with a history of more live births, with scores of 9.0 for those women with zero births, 8.7 for those with one to two births, 8.5 for three to four births and 7.8 for those women with five or more live births.

After standardizing the data to remove or account for ethnic, education, income and other socio-economic factors that might skew the data, the investigators found that women with five or more births were 50% less likely to have optimal cardiovascular health scores. For example, of the 453 women with five or more births, only 35 women had optimal cardiovascular health compared with 279 who had the lowest health scores. Even the odds of having an average rating for cardiovascular health were approximately 35% lower for women with any number of live births compared with women with no live births.

Overall, women with five or more births were more likely to be Hispanic, more likely to have high blood pressure or blood sugar, and reported lower incomes.

"The next steps for this research will be to design a study to determine if there is a causal relationship between higher number of live births and poorer cardiovascular health," says Oluseye Ogunmoroti, M.D., M.P.H., the lead author and biostatistician in the Ciccarone Center, "in addition to exploring the biological mechanisms by which more live births may worsen cardiovascular health."