Fast-forward to several decades or a half-century from now, and it’s not inconceivable that humans could be living on Mars—building habitats, trundling around in rovers, mining the subsurface for resources, and producing the first generation of bipedal Martians.
Except, no one really knows if humans can successfully reproduce in space, whether that’s during spaceflight or on another planet. To be clear, having sex in (much) lower gravity is a simple physics problem. But a host of unknowns swirl around how space environments affect the actual biological sequences of events that must unfold with precision for a new human to grow, from fertilization to weaning.
For a long time, doctors considered 37 to 41 weeks of gestation “full term” but new evidence has prompted the definition to be tightened to between 39 and 41 weeks.
The report, to be released by Federal Health Minister Greg Hunt on Tuesday, found up to 60 per cent of planned caesarean sections are occurring before 39 weeks and up to 22 per cent before 37 weeks for no good reason and against guidelines.
It’s not as though we haven’t tried to sort it out. Mice, rats, salamanders, frogs, fish, and plants have been the subjects of experiments looking at how spaceflight affects reproduction. To put it simply, though, the results so far are mixed and inconclusive.
On Earth, evolutionary processes are fine-tuned to work in an environment characterized by one of our planet’s most basic forces: gravity. In space, gravity is essentially nonexistent, and on Mars it’s about 38 percent the strength of Earth’s downward pull. So far, no one has even come close to figuring out how a partial gravity environment could affect mammalian reproduction.
As well, radiation in space is stronger and potentially more damaging than down here on the ground, because Earth’s magnetic field helps shield the planet from energetic cosmic particles. High radiation doses are already a serious concern for adult space travelers, and space agencies carefully track their astronauts’ exposures in orbit. What that radiation could do to a much more developmentally sensitive fetus is a real worry.
The effects of those two things—gravity and radiation—on reproduction are, so far, the major issues scientists are trying to address. And because of ethical qualms associated with studying medical risks in humans, scientists have spent decades launching various other animals and associated tissues into space.
Early experiments done by the Soviets in the late 1970s included sending several rats into orbit aboard the Cosmos 1129 satellite. When they returned, there was evidence that they’d mated in space, but none of the females ever delivered, which might not be surprising to anyone who studies rodents, given their sensitivity to environmental perturbations.
Later, NASA scientist April Ronca sent pregnant rats into orbit and observed how spaceflight affected the later stages of pregnancy; back on Earth, the birthing process was more or less normal, but other work suggests thatrat pups exposed to microgravity develop abnormal vestibular systems, or the inner-ear machinery associated in sensing movement direction and orientation.
In mice, the story is similarly complicated. Research suggests that the two rodent species respond differently to changes in gravity. Two-cell mouse embryos sent into space aboard the shuttle Columbia failed to develop further, even as Earth-based controls matured normally. Later, work in simulated microgravity (achieved using a rotating piece of machinery called a clinostat) showed that while in vitro fertilization could occur normally, microgravity-cultured embryos transferred to female mice failed to implant and develop at normal rates.
Most recently, a Japanese-led study found that freeze-dried mouse sperm could produce embryos after spending nine months in space. Other work shows that crickets, nematodes, and fruit flies can successfully reproduce when spaceflight is involved. And Japanese medaka fish mated and produced offspring while on board the space shuttle Columbia.
Taken together, these experiments and others aren’t exactly constructing a cohesive image of how spaceflight affects reproduction.
“If you were to take reproduction and break it down into all of its various parts … there’s never really been a dedicated scientific program that looks at how each of those steps is affected by the space environment,” Lehnhardt says. “It’s one thing to know that it’s even possible, it’s another thing to know that it can be done safely and have a good outcome.”
In general, though, it’s not looking good for mammals, in which successful embryonic development starts with a complicated interchange between mom and fetus and just gets more complex from there.
“Across the board, almost every study has shown that in space, either things don’t work at all or they’re not as good—and so as we move forward, we need better and bigger studies, and human studies,” says James Nodler of the Houston Fertility Clinic, who reviewed the links between gravity and embryonic development.