Just one pregnancy can add months to your biological age

Surprising no one who has ever been pregnant, scientists have found that growing a human being from scratch makes your body “older."

New research suggests that a single pregnancy can add between two to 14 months to your biological age. 

“Pregnancy has a cost that appears to be detectable even" as early as your 20s, says study leader Calen Ryan, a human biologist at Columbia University’s school of public health in New York City.

It’s a “landmark study” that reaffirms what women already know—pregnancy takes a tremendous toll on the body, says Yousin Suh, a Columbia University professor who researches how pregnancy affects aging and wasn’t involved in the study, published April 8 in Proceedings of the National Academy of Sciences. 

Your chronological age—or the number of trips you’ve made around the sun—may be different than your biological age, which is how old your cells and organs seem based on their biochemistry. 

Ryan studies the reasons why our bodies may age faster or slower than we expect them too, and a lot of that comes down to epigenetics, or how and when our bodies decide to turn genes on and off. (Read how scientists are finally studying women's bodies—and what they're learning.)

Certain life events—including major illnesses, trauma, or periods of intense stress—seem to cause “jumps” in epigenetic age as the body redirects energy and resources toward coping with these challenges.

And since there are few biological functions more arduous than growing an entire person in just nine months, the recent study confirms the scientists’ suspicion that pregnancy—particularly multiple pregnancies—come at a cost to biological age.

Your epigenetic clock

If our genome is an instruction manual, the epigenome is a complex system of bookmarks, highlights, and underlines that tells our cells which genes to read and when. This often happens through methylation, a process by which tiny chemical tags called methyl groups attach to a section of DNA.

Which genes need to be active changes constantly in response to our environment and experiences, so those methyl groups need frequent moving and replacing. Yet as we age, this maintenance machinery appears to start making errors, causing methylations to accumulate in some places and disappear in others. (Read how influencing your genes could help you live longer.)

By taking a blood sample and tallying methyl bookmarks in key locations along the genetic code, scientists can calculate a person’s epigenetic age via a suite of algorithms called “clocks.” These clocks predict your risk of death and health complications, but less known is how fertility impacts your biological age.

To learn more, Ryan and his colleagues turned to a long-running study on intergenerational health in the Philippines. In 2005, they analyzed blood samples from 825 women participants between the ages of 20 and 22. (Learn about simple innovations that could help millions of pregnant women.)

The scientists identified a striking difference—the number of epigenetic changes in their DNA revealed that women who had been pregnant were between four and 14 months were biologically older than their peers who hadn’t, even after controlling for factors such as income level and smoking habits.

A cumulative effect

Despite being close in age, the women in the study were already on very different fertility trajectories—some had never been pregnant, some reported one or more previous pregnancies, and some were pregnant at the time the samples were collected.

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That raised a crucial question: Did multiple pregnancies create a cumulative effect of aging, with each additional pregnancy further raising the mother’s epigenetic age?

Using the first blood samples as a baseline, the researchers collected new samples from 331 of the same women while they were pregnant between four and nine years later. (Learn how babies develop in the womb.)

By comparing the two snapshots of each woman’s epigenetic age, Ryan and his team calculated the impact of each additional pregnancy during the intervening years.

“Women who had more pregnancies during that time had more change in epigenetic aging,” Ryan says, with each pregnancy tacking on two to three months to the parent’s biological age.

Suh, who studies the cost of reproduction on the human body, says Ryan’s findings represent an important advancement in our understanding of how multiple pregnancies affect biological age, as the bulk of existing research has examined just one pregnancy.

The new research, she says, squares with what we know about high birthrates—that experiencing many pregnancies can lead to a shorter life span and higher risk of cardiovascular disease.

Reason for optimism 

But would-be parents shouldn’t despair, Suh and Ryan agree—it’s not certain that a slightly higher epigenetic age during your childbearing years will lead to complications decades down the road.

In fact, some research suggests there may be a “sweet spot” for fertility, Suh says. For instance, one or two pregnancies may be better than none in some cases, as pregnancy is linked to lower risks of certain cancers and having at least one child is associated with a slightly longer life expectancy.

As scientists learn more about aging and fertility, “we can work towards identifying people who might be at higher risk,” Ryan adds, and come up with strategies to lessen the negative impacts of pregnancy.

Recent studies indicate the epigenetic cost of pregnancy may differ by country and culture, suggesting that parental support and access to healthcare may play a significant role—improving these could soften pregnancy’s blow to epigenetic age.

Suh adds more research will be needed to untangle the impact of child-rearing from childbirth on epigenetic age, as well as investigate whether the burden of pregnancy is greater when parents are older than those in the study.

While it may feel like common knowledge that pregnancy ages you, it’s a relatively new concept in the scientific literature—and Suh says that research like Ryan’s is long overdue.

“I’m so encouraged that this kind of study is now being done,” she adds.