New research recently published in the Journal of the American Heart Association shows that women who became mothers for the first time as teenagers may be at a much greater risk of cardiovascular disease than older first-time mothers.

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Giving birth in our adolescent years should be avoided, suggests new research.

The new study was led by Catherine Pirkle, Ph.D., an assistant professor in the Office of Public Health Studies at the University of Hawaii at Manoa in Honolulu. The first author of the paper is Nicole Rosendaal.

Prof. Pirkle and her team examined the data available on 1,047 women from the 2012 International Mobility in Aging Study (IMIAS). The women were between 65 and 74 years old and were living in Albania, Brazil, Canada, and Colombia.

Having obtained information on the age of the women's first pregnancy, the researchers used the Framingham Risk Score (FRS) to check for correlations with cardiovascular disease risk.

Cardiovascular disease — understood as heart disease and the blood vessel-related problems that give rise to it — is the leading cause of death among both men and women in the United States.

The new study found that women who had their first pregnancy before the age of 20 had a much greater long-term risk of cardiovascular disease than women who became mothers after that age.

Additionally, women who had never given birth had the lowest cardiovascular risk, as measured by the FRS.

Speaking to Medical News Today about the strengths of the study, Prof. Pirkle deemed the findings "robust." She explained:

"Women who participated in our study came from five very different study sites. We observed a relatively consistent association in which early childbearing was associated with greater cardiovascular disease risk across study sites, which supports the validity of our results."

In addition to the diverse sample of the study, Prof. Pirkle spoke to MNT about its other strengths, such as the researchers having used the laboratory-based version of the FRS to measure heart disease risk.

"Because this version of the [FRS] largely uses biomarker measures (e.g., blood test results) and clinical measures (such as blood pressure)," Prof. Pirkle explained, "it is less prone to the biases often encountered in observational epidemiological studies that rely on participant self-report."

"We also repeated our analyses using office-based [FRS]," she added, "which are what doctors might ask during a clinical evaluation, and observed very similar results."

The study authors admit, however, that the study has some limitations. For one thing, the research used data as they were reported by the study participants, who were seniors.

This puts the study respondents at risk of memory loss, which may have biased the results, says the team.

Prof. Pirkle shared with us an additional potential limitation, which also has to do with the advanced age of the participants.

"Because the IMIAS includes study sites from middle-income settings," she explained, "especially Brazil and Colombia, where premature mortality was high when these women were younger, there is a possibility that we only selected 'survivors' for our study."

"It is possible that women who were at highest risk of cardiovascular disease mortality died before we could recruit them to our study. This is termed survivor bias," Prof. Pirkle continued.

Although this was an observational study that cannot explain causality, Prof. Pirkle shared with us two potential explanations for the strong association between teen motherhood and heart disease risk.

These mechanisms "are not mutually exclusive," she said.

"The first mechanism," Prof. Pirkle went on, "relates to the consequences of adolescent pregnancy and childbirth […] Adolescents who have children early in life may have [fewer] opportunities to finish school and to earn sufficient incomes over their lifetimes."

"In turn, they could experience more unhealthy stress and engage in poorer behaviors, such as smoking, which increases their cardiovascular disease risk," she said.

"Another possible mechanism," Prof. Pirkle added, "may be that pregnancy and childbirth during a critical developmental period such as adolescence, compared to adulthood, permanently alters certain physiological pathways in ways that may be harmful to the heart over time."

"There is some evidence to support the [latter] mechanism, but my best guess is that social and behavioral consequences of adolescent childbearing are much more powerful," she noted.

Prof. Pirkle puts this down to other studies having shown that men who become parents in their adolescence are also in poorer health than older men and face many of the same negative consequences that mothers do.

"This suggests that the consequences of adolescent childbearing," said Prof. Pirkle, "such as less social and economic opportunities, are driving the association that we observed in our study."

However, in an effort to fully elucidate these mechanisms, the research team plans to investigate further, using population samples from Canada and the U.S.

"By better understanding the pathways that link adolescent childbearing to later life cardiovascular health, we will be able to identify prevention opportunities and make recommendations for policy," Prof. Pirkle explained.

In a separate research project, Prof. Pirkle and her colleagues are "comparing key cardio-metabolic biomarker measures in pregnant adolescents [with those in] pregnant adult women to see if there are any differences between these two groups."

"Whatever the mechanisms, our results reinforce what is already broadly accepted by most societies: adolescent childbearing should be avoided."

Catherine Pirkle, Ph.D.