Getting Pregnant Again Too Soon May Speed Up Biological Aging, Scientists Say

Pregnancy remodels a woman’s hormones, immune system, and metabolism, and scientists are still working to determine how much of that reverses after the baby arrives, and how much lingers.

A peer-reviewed review published October 22 in the journal Trends in Endocrinology & Metabolism focuses on one piece of that puzzle: what happens when a new pregnancy begins before the body has recovered from the last one.

The authors synthesized existing research to make their case, and they arrive at an eye-catching idea. They suggest the breathing room between pregnancies may say more about a mother’s long-term aging than how many pregnancies she has had.

Independent experts who weighed in find the idea interesting, and some call it plausible. They also keep coming back to a surprisingly basic question: how do you measure aging in the first place?

Pregnancy Can Push Biological Age Up, Then Back Down

Scientists estimate biological age from the body’s inner workings, and it says nothing about how old a mother looks.

Biological age tracks changes in cells, tissues, and organs, separate from how many years someone has lived. Penn State’s Idan Shalev and Laura Etzel explain that researchers commonly estimate it with epigenetic clocks, mathematical models built on patterns of DNA methylation. Telomere length and clinical markers are other options.

Pregnancy appears to move that clock. Jesse Poganik, the review’s corresponding author at Harvard Medical School, says his earlier research found that estimated biological age rises temporarily, peaking around the third trimester or at delivery. After birth, it comes back down, at least partly.

What happens if another pregnancy starts while the body is still winding things back?

Related: 15 Ways to Think About Pregnancy That Show Just How Crazy the Human Body Really Is

Why The Time Between Pregnancies Could Matter

The first half of this story is based on observation, while the second half is still an idea awaiting proof.

The review, “The postpartum recovery window as a determinant of maternal aging,” comes from Poganik and co-author Albright. It gathers existing research and describes no new group of participants.

In the authors’ telling, a pregnancy that arrives before recovery is finished could interrupt it. Repeated interruptions might let changes accumulate across pregnancies, so a mother’s recovery time could shape how she ages over the long run.

Poganik frames the open question as how those short-term shifts relate to aging across an entire lifetime. “It’s possible that this could change the overall trajectory of aging,” he said in a Cell Press release, adding that these changes don’t necessarily equate with biological damage.

Experts Like The Idea But Urge Caution

Three independent expert groups called it interesting, then listed what it can’t prove yet.

Calen Patrick Ryan, of Columbia University’s Robert N. Butler Columbia Aging Center, didn’t soften it. “I would emphasize that this is a hypothesis.” He said the paper can’t show that closely spaced pregnancies speed up aging, and it can’t say how long a gap would count as enough recovery.

Shalev and Etzel called it a novel, testable framework. What studies haven’t established, they said, is that shorter intervals cause lasting acceleration of biological aging, or that they raise long-term mortality through this mechanism.

Yolanda Cabello, director of the Nebrija Mallorca University Center, found the hypothesis intriguing and plausible. Researchers have seen associations between pregnancy intervals and certain obstetric and perinatal outcomes, she noted, but that doesn’t show that a short interval alone raises biological age.

The Measuring Tools Have Their Own Problems

The numbers at the center of this story can be read two ways.

Cabello draws a line between changes in biological-age markers and the body’s actual, permanent aging. Ryan adds that most of these measures were developed in people who weren’t pregnant, so when they shift during pregnancy, nobody yet knows how much reflects lasting costs and how much reflects the body adapting. Inflammation or a different mix of cells being measured could produce the same shift.

The spacing itself is shaky ground too. Ryan questions whether time between births reliably captures recovery at all, since health, stress, fertility, breastfeeding, access to contraception and social and economic support can all influence both when someone becomes pregnant again and how she’s doing afterward.

Does This Change Anything For Mothers Right Now?

The only spacing advice in the picture was around long before this review.

The World Health Organization already recommends waiting at least 24 months after a live birth before conceiving another child, the Cell Press release notes, intending to reduce health risks for mother and baby.

That clock runs from delivery to the next conception, which Shalev and Etzel call the interpregnancy interval, rather than from one birth to the next.

The review doesn’t propose a new interval based on aging, and Poganik says more research is needed before anyone can make recommendations on that basis. The work offers no screening test, treatment, or personal conception timetable.

If you’ve had more than one baby, what shaped how long you waited between pregnancies?

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