There's no question that having children imparts considerable stress, affecting just about every part of the body.

In spite of this universal truth of parenthood's health costs, there is no standard for measuring the biological accounting demanded of a mother during gestation.

A new study led by researchers from Yale University could help us better understand the forces behind cellular aging during and after pregnancy.

Research into human DNA and its accumulation of molecular edits over time – a phenomenon described as biological aging – has shown the sheer effort of bearing a child on the body's cells. It's in line with harrowing events like surgery and major illness, literally adding years of changes to a childbearer's cells.

Fortunately, the baggage that comes with such stressful events may also be transient and reversible. Studies have shown that unlike our birthdays, our biological age can stop and even rewind once the stressful times come to an end.

A recent analysis of blood samples taken from 119 women at various stages of pregnancy and after delivery adds intriguing detail to those previous findings. It demonstrates a "pronounced reversal of biological aging" following delivery.

Some breastfeeding mothers even experienced a genetic fountain of youth, with their biological age reversed to a time well before they had conceived.

While the measures hint at a remarkable ability for bodies to bounce back from the profound changes that come with pregnancy, senior researcher Kieran O'Donnell emphasizes we have so much more to learn about the mechanisms at work.

"Lots to follow up on here," says O'Donnell, a reproductive scientist at Yale.

"First, we don't know if the postpartum recovery effect is relevant for short or long term maternal health outcomes and if these effects accumulate over successive pregnancies. Likewise, we don't know if the postpartum decrease in biological age is simply the system recovering to pre-pregnancy biological age or, more provocatively, if pregnancy may have a rejuvenating effect."

All kinds of environmental hardship can cause organisms to slap chemical padlocks on certain genes to better manage their biological functions. These so-called epigenetic changes not only remain in place as cells divide and multiply, they can also be passed on down to following generations.

As a measure of biological age, epigenetics can serve as a kind of standard clock for senescence, allowing us to compare the state of function between different individuals. A traumatic life of limited nutrition, fear, or ill health can result in amendments to a cell's nuclear material, compared with a person who had a childhood of love and fine food.

Thanks to the study conducted by O'Donnell and his team, we might now presume a mother's cells add roughly 2.5 years of epigenetic edits in just 18 weeks of gestation, covering early to late pregnancy.

Weight gain during pregnancy did not contribute to epigenetic change, the team found, although a mother's BMI prior to pregnancy was associated with increased cell aging while she was pregnant.

While sleepless nights, sore backs, and endless diaper changes have their own stresses, the delivery of a newborn comes as a welcome relief to the mother's body, which reduces biological age by as much as three times the amount that age had increased early in the pregnancy. For mothers who reported breastfeeding, their postpartum state of epigenetic changes could even amount to a far younger biological age than what was measured at the commencement of pregnancy.

This research was published in Cell Metabolism.