Humans Might Struggle to Make Babies in Space. Sperm Gets Disoriented in Microgravity, a New Study Suggests

Simulated near-weightless conditions reduced human sperm’s navigational abilities

Margherita Bassi | Daily Correspondent

April 1, 2026

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Floating in near-weightless conditions can be disorienting for even the most experienced astronauts. Male reproductive cells—sperm—also seem to get confused in simulated microgravity, which has implications for human reproduction in space, according to a study published March 26 in the journal Communications Biology.

Near-weightlessness “causes [sperm] to flip around, to go upside down.… They don’t really know which way is up or down,” Nicole McPherson, a study co-author and a biologist at Adelaide University in Australia, tells the Guardian’s Tory Shepherd. The cells do “not really understand or know which direction they’re going in.”

NASA aims to establish a long-term human presence on the moon and Mars, raising questions about humans’ ability to reproduce offspring and breed animals there. While previous studies have explored how sperm’s mechanical movement in space environments, whether the cells can successfully navigate the female reproductive tract and fertilize eggs has remained an open question.

So, on Earth, McPherson and her colleagues put sperm from humans, mice and pigs in a device that rotates the cells in all directions, mimicking microgravity. They examined how well the sperm could navigate tiny mazes that resembled female reproductive tracts while being spun.

While around 50 percent of human sperm made it to their destination in Earth’s gravity, less than 20 percent of them reached the finish line in near weightlessness, even though microgravity didn’t affect the cells’ mechanical movement. Mouse sperm behaved similarly.

“Many of the proteins found on sperm act as mechanosensors, tiny molecular devices that detect physical forces,” McPherson tells Live Science’s Kenna Hughes-Castleberry in an email. “Remove the force of gravity, and it stands to reason that these sensors would be thrown off, disrupting the sperm’s ability to orient and navigate.”

However, adding high amounts of the hormone progesterone, which is produced by the female reproductive system after ovulation, helped sperm overcome disorientation in microgravity, the team found. “We believe this is because progesterone is also released from the egg and can help guide sperm to the site of fertilization, but this warrants further exploration as a potential solution,” McPherson says in a statement.

The team also investigated the impact of microgravity on fertilization and early embryo development using mouse and pig sperm and eggs. Compared to Earth conditions, the simulated space environment led to lower fertilization rates of cells from both animals. Some embryos developed from the few successful events in microgravity, although prolonged exposure to it resulted in certain signs of developmental delays in mice.  

“After fertilization, the embryo still needs to implant into the uterine wall,” a process that requires gravitational signals, McPherson tells Live Science. “Then the embryo’s cells must organize themselves correctly to eventually form every organ in the body, sustained by a placenta that must function properly for the full duration of pregnancy. Microgravity has the potential to disrupt any or all of these stages.”

Still, many of the embryos fertilized in space conditions contained healthy cells, so the researchers are hopeful about the future possibility of making space babies. Next, they plan to study sperm navigation and early embryo development in varying gravitational environments, like those on the moon and on Mars, which have gravity levels below that on Earth but higher than microgravity.

“As we progress toward becoming a spacefaring or multi-planetary species, understanding how microgravity affects the earliest stages of reproduction is critical,” says John Culton, director of Adelaide University’s Andy Thomas Centre for Space Resources, in the statement.

Margherita Bassi | Read More

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.