Space Is Bad for Making Babies, New Chinese Research Confirms

A Major Hurdle for Humanity's Space Ambitions

If humanity ever hopes to build permanent colonies on the Moon or Mars, we'll need to figure out how to reproduce beyond Earth. A landmark new study from Chinese scientists has delivered a sobering reality check: space is a deeply hostile environment for human reproduction — and the numbers are stark.

Early-stage human reproductive cells did not grow or develop nearly as well in space as on Earth, according to a team from the Chinese Academy of Sciences' Shanghai Institute of Technical Physics and Beijing's Tsinghua University. In space, the success rate of generating the earliest precursor germ cells falls by around half, while early sperm-producing cells multiply over 25 percent more slowly. The outcome was attributed largely to microgravity and cosmic radiation.

The findings were published in the journal Science Advances on July 15. That makes this one of the most detailed and rigorously documented studies of human reproductive biology ever conducted in orbit — and the results raise serious questions about what long-duration spaceflight means for the future of our species.

Years in the Making: The Tianzhou Experiments

The researchers used two of China's Tianzhou cargo spacecraft missions to culture and study the differentiation of human reproductive cells in space. During the Tianzhou-1 mission, launched on April 20, 2017, the team achieved a 30-day in-orbit differentiation culture of primordial germ cells induced from human embryonic stem cells. The later Tianzhou-6 mission, launched on May 10, 2023, resolved earlier technical limitations and enabled the differentiation of multiple germ cell types under spaceflight conditions, including real-time fluorescence imaging and the collection of matched datasets from both the spacecraft and a ground control group.

The researchers utilized an automated bioreactor that supported long-term differentiation of human embryonic stem cells into primordial germ cells, ovarian follicle precursors, and spermatogonial stem cells aboard the spacecraft. This also marks the first time in the world that scientists have successfully differentiated human embryonic stem cells into germ cells in a space environment. In other words, this wasn't just a measurement study — it was a genuine biological first.

The Numbers Are Troubling — But Not Catastrophic

In a space environment, the rate of formation of primordial germ cells — the earliest precursors of reproductive cells — is reduced by about half, while early-stage spermatogenic stem cells proliferate more than 25 percent slower. The research also revealed cell-type-specific disruptions in extracellular matrix organization, microtubule dynamics, and lipid metabolism. Together, these findings paint a picture of a biological system under real and measurable stress.

There is, however, a sliver of encouraging news buried in the data. Analysis after the samples returned to Earth showed that, although genetic damage to reproductive cells increased with the duration of exposure, a 15-day period did not cause widespread genetic damage. That's a meaningful distinction. Short missions may not permanently compromise reproductive potential — but the longer astronauts spend in space, the more the risks appear to compound.

What This Means for the Future of Space Colonization

Humanity's looming ambition to colonize the Moon and Mars faces one major obstacle: our ability to reproduce beyond Earth. While we're nowhere near making space babies just yet, now may be the time to begin understanding the exact risks of trying. This research moves that understanding forward in a concrete way.

Given these challenges, it may be necessary to turn to in vitro fertilization to help grow babies in space — an idea already being explored by several private space exploration companies. Scientists say the study will help reveal the risks and challenges humans might face during long-term space habitation, particularly regarding reproduction. By comparing space-grown cell models with those on Earth, the research could also provide fresh insights into which human diseases are linked to abnormalities during the earliest stages of life. The implications, in other words, stretch well beyond astronauts — they touch on our fundamental understanding of human development itself.