You don’t need me to tell you that pregnancy can be rough on a body. There are so many things going on during the gestation of a fetus that one might feel that those nine months are years long. Some people get their youthful feelings back once the baby is born, but plenty of others don’t. This isn’t new information. Mothers have experienced the same symptoms for ages on end.

The scientific study of pregnancy and how cells change continues to be an area of study yielding valuable information. There is so much more that we don’t know than what we think we know. Studies published this past week, however, caught us by surprise as they revealed a cellular elasticity that hadn’t been expected. During pregnancy, a woman’s cells can age as much as two years beyond her calendar age. Sometimes the cells regain some of the youthfulness, even appearing younger than they did prior to the pregnancy. Other times, they remain the older age and continue to age with each subsequent pregnancy. In other words, for some women, the more children you have, the older you’re getting.

I know. Some women are reading this and thinking, “Yeah, and that’s surprising how?”

The fundamental importance of this research isn’t so much the degree to which pregnancy ages a person, but the proof that aging isn’t linear. Perhaps we shouldn’t have been as surprised as we are. After all, we’ve known time isn’t linear. Einstein’s Special Theory of Relativity showed us a different way of looking at time that hadn’t been considered, or provable, before. If time isn’t linear, then it makes sense that aging, which is dependent on time, wouldn’t be linear either. Yet, we continue linearly counting our age.

The journal Cell Metabolism published an article this week titled, “The effects of pregnancy, its progression, and its cessation on human (maternal) biological aging.” What they discovered was interesting. In their words, “In mice, the authors reported evidence for pregnancy-associated biological aging, with a partial reversal of this effect after the cessation of pregnancy (i.e., in the postpartum). They also observed pregnancy-associated biological aging in humans, with suggestive evidence from a cohort of 14 women that these effects may be partially reversed in the postpartum.”

Human translation: Working from evidence in mice that pregnancy results in the actual aging of cells, they looked for similar findings among women and observed that not only do women age faster during pregnancy, but that in 14 women, the effects were partially reversed after the baby was born. Are you staying with me here? Yeah, you feel older during pregnancy because your body really is biologically aging faster than you would if you weren’t pregnant. But some women actually see a reversal of that aging post-partum!

The surprise of regenerative cellular development sits in the middle of some not-so-surprising news. In general, pregnancy is rough on the body. When researchers “analyzed changes in blood samples taken during early, mid, and late pregnancy, they found unusually high amounts of chemical wear and tear. That included levels of DNA methylation that they would expect to see in people 1 or 2 years older than the study participants actually were. In other words, the stress of pregnancy may have caused their biological age to increase faster than their chronological age.”

This “wear and tear” is particularly concerning because of the degree to which it makes women more susceptible to disease. While that “aging” process typically peaks in the third trimester, the effects linger. The result is women appear more fragile and prone to serious illness, including cancer and heart disease, after pregnancy. That’s a pretty damn important matter to consider when thinking about whether to add to the planet’s burgeoning population.

But wait! There’s good news!

According to the research, “blood samples from 68 participants, collected 3 months after giving birth, revealed a dramatic about-face. Although being pregnant had initially aged their cells between 1 and 2 years, O’Donnell says, their biological age now appeared to be 3 to 8 years younger than it had been during early pregnancy—with different epigenetic clocks algorithms providing slightly bigger or smaller estimates. The effect appeared to be slightly muted in people who had a higher body weight prior to pregnancy, whereas it was enhanced in women who reported exclusively breastfeeding.”

So now, while one might age a couple of years during pregnancy, they might end up three to eight years younger than when they started! That would mean less body wear and tear, making one healthier. The caveats are that the type of epigenetic clock algorithm used to calculate age makes some difference, higher body weight reduces the effects, and women who exclusively breastfeed come out the best.

Obviously, findings like this demand further investigation. For example: if a 25-year-old woman ends her first pregnancy a net five years younger at six months post-partum, then ends a second pregnancy three years younger two years later, is she, physiologically, only 19 years old? What are the dominating factors in determining who does and who doesn’t experience the regenerating effect?

I know some people look at the research and respond that we’ve known that aging is not linear because of the effects of diet and exercise. May I point out that the effects generated by intentional actions are not identical to those generated by biological processes? You change your diet and exercise habits knowing the potential for physiological change. What this research indicates is that physiological rejuvenation may be part of the natural process of childbirth, not something cultivated by intentional activity.

This is exciting research that could begin to help us answer questions about premature aging, the development of health problems, and why the US mortality rate is so fucking steep. Plus, it’s nice to know that there are physical benefits to having a child that test your patience and sanity at every turn.

Perhaps next they can work on eliminating morning sickness.