Close-together pregnancies may stack up on aging tests, review argues

Pregnancy can make a woman’s body look years older on biological aging tests, and some of that apparent extra age seems to fall away after the baby is born.¹ A new review from researchers at Harvard Medical School asks what happens when a second pregnancy starts before that recovery is finished. Their answer, which they stress is still a hypothesis, is that the changes might pile up.¹²

What the review says

The paper was published on October 22, 2026, in the journal Trends in Endocrinology & Metabolism. It was written by Stephen Albright and Jesse Poganik of Brigham and Women’s Hospital and Harvard Medical School (one report spells the second name Poganick).²¹ It is a review: the authors summarize results from earlier studies and offer a new explanation, rather than reporting new data of their own.²

They call their idea the recovery period hypothesis. Each pregnancy brings a temporary rise in aging-related measures, which may come back down after delivery. If another pregnancy begins before that decline is complete, the leftover change might accumulate.¹ In Poganik’s words:

“If the window is cut short by another pregnancy, the costs may compound across pregnancies.”

That quote was reported by ZME Science.¹ The authors describe the gap between pregnancies as a possible “missing variable.” It might help explain a puzzle: in some population studies, having more births is linked to worse health for mothers, and in others it is not.²

The evidence the review builds on

“Biological age” is not the number of birthdays a person has had. It is an estimate of how old the body appears, based on changes in DNA, blood chemistry and other signs of how organs are working.¹ One common way to measure it is an epigenetic clock, a test that reads chemical changes on DNA that shift with age.²

Several earlier studies feed into the review’s idea:

• A rise and a partial fall. A 2024 Yale-led study of 119 women, published in Cell Metabolism, found DNA-based clocks moved forward by about two years over roughly 20 weeks of pregnancy.¹² Three months after delivery, some of those readings had dropped sharply.¹
• A slow reset. A 2025 analysis of more than 300,000 pregnancies looked at 76 lab measures. About half took months, sometimes up to a year, to return to their usual levels after birth. Blood-clotting measures mostly settled fast; some liver enzymes and metabolic markers took much longer.¹
• A hint about the next pregnancy. A 2026 study followed 130 mothers, measuring aging markers during pregnancy, again about six to nine months after delivery, and again three to four years later. In women who became pregnant again, the usual slowdown in a measure called DunedinPACE, which estimates how fast someone is aging, was interrupted.¹
• More children is not simply worse. A Finnish study of nearly 15,000 women found that those with two or three children had the lowest risk of dying during the study, while women with no children or five or more had higher risks.¹

Pregnancy asks a lot of the body. Blood volume can grow by 40% to 50%, the immune system reorganizes, stress hormones rise, and a temporary organ, the placenta, forms.¹ Brain scans have also shown changes in gray matter during pregnancy, followed by partial recovery, which ZME Science notes does not mean pregnancy damages the brain.¹

Earlier work points the same way from another angle. A 2024 Columbia University study of 1,735 young people in the Philippines, published in the Proceedings of the National Academy of Sciences, found women who reported more pregnancies looked biologically older on epigenetic clocks. The number of pregnancies men had fathered showed no such link.³ Its lead author, Calen Ryan, noted that many of those pregnancies happened in late adolescence, while the mothers were still growing.³

What it does not show yet

The authors and outside experts are clear that this is an idea to test, not a finding. It has not been shown that a short gap between pregnancies leads to permanent faster aging or a shorter life.² The evidence that pregnancy temporarily changes aging markers is described as convincing; whether closely spaced pregnancies cause lasting harm is an open question.¹

The 130-mother study did not work out how many months of spacing matter, or whether the changes last into old age.¹ The Finnish study did not look at spacing at all, so the review’s suggestion that recovery time could explain its pattern is untested.¹

Yolanda Cabello, a nursing lecturer at Nebrija University Centre Mallorca, told Science Media Centre Spain:

“Of course, it is critically important to distinguish between changes in the markers we use to estimate biological age and actual permanent ageing of the body.”

She added that it “has not yet been demonstrated” that short gaps are responsible for the apparent effects, or that such changes lead to meaningful long-term health outcomes.¹

There is also a wider question about the tests themselves. Aging clocks are used as shortcuts because studies of real outcomes, such as heart attacks, cancers, dementia and deaths, would take around 20 years. Physician Peter Attia’s podcast has discussed the uncertainty about their clinical value, the “noise” that affects how reliable some clocks are, and why they are not yet reliable as consumer tools.⁴ A 2023 Johns Hopkins review of 68 studies using epigenetic clocks in children found that most reported links with health outcomes or exposures, but that the findings were somewhat mixed.⁵ Ryan, of the Columbia study, said researchers do not know how far accelerated epigenetic aging will show up as poor health decades later.³

Who is behind it

The review comes from academic researchers at Brigham and Women’s Hospital and Harvard Medical School.² The reports read for this article do not describe who funded the work or whether the authors have any company ties.

Many things besides the calendar may affect recovery after birth. Weight before pregnancy and breastfeeding have been linked to differences in aging-clock readings after delivery. Sleep and long-term stress may matter too, but the review notes their effect on recovery remains largely untested.¹ Individual health is likely another factor.²

How it fits with existing guidance

Advice on spacing pregnancies already exists, built on other risks. The World Health Organization recommends waiting at least 24 months after a live birth before trying for another pregnancy, to reduce risks to mothers and babies.¹ The American College of Obstetricians and Gynecologists advises avoiding a new pregnancy in the first six months after birth and discussing the risks of a gap shorter than 18 months with a doctor.²

Those recommendations rest on links between short gaps and higher chances of premature birth and low birth weight, and in some cases after a previous cesarean section, a higher risk of the uterus tearing.² They measure time from birth to the next conception, not between two births, and the right interval depends on the person, for example for women over 35 or those who have trouble conceiving.² The review adds a separate, unproven question: whether the gap might also matter for a mother’s own health decades later.²

What to watch next

The authors say the idea can only be confirmed by long-term studies that follow women before, during and after several pregnancies in a row.² Key questions for such work include how many months of recovery make a difference, whether aging-test changes that build up between pregnancies persist into later life, and whether they track real health outcomes rather than just test scores.¹⁴

Biohack will follow this thread as studies that measure pregnancy spacing and biological age directly are published.