Starting a family off-planet can be more difficult than expected. New research from the University of Adelaide shows that sperm have a harder time moving in lower gravity, suggesting gravity plays a key role in reaching the egg.
Scientists from the Robinson Institute, the School of Biomedical Sciences, and the Masonic Center for Men’s Health and Welfare studied how space-like conditions affect sperm navigation, fertilization, and early embryo development.
To simulate microgravity, the researchers used a 3D clinostat machine developed by Dr. Giles Kirby of Firefly Biotech. The device continuously rotates the cell to mimic the disorienting effects of weightlessness. The test involved sending sperm from three different mammals, including humans, through a labyrinth designed to resemble the female reproductive tract.
“This is the first time we have been able to show that gravity is an important factor in the ability of sperm to move through pathways such as the reproductive tract,” said lead author Dr Nicole McPherson, from the Robinson Research Institute at the University of Adelaide.
“Under microgravity conditions, we observed a significant reduction in the number of sperm that successfully passed through the chamber maze compared to normal gravity conditions.
“This was correctly experienced in all models despite no change in the way the sperm physically moved. This shows that the loss of sperm orientation is not due to changes in motility, but to other factors.”
Progesterone may help guide sperm
The researchers also found that adding the sex hormone progesterone helped human sperm migrate better under simulated microgravity conditions.
“We think this is because progesterone is also released by the egg and helps guide sperm to the fertilization site, but this requires further research as a potential solution,” Dr McPherson said.
Effects on fertilization and embryo development
The research team investigated how exposure to microgravity during fertilization affects early embryonic development in animal models.
After four hours in simulated weightlessness, the number of successfully fertilized mouse eggs was reduced by 30% compared to normal Earth conditions.
“We observed a reduction in fertility after four to six hours of exposure to microgravity. Longer exposures appear to be even more harmful, slowing development and, in some cases, reducing the number of cells that will form a fetus during the early stages of embryogenesis,” said Dr. McPherson.
“These insights demonstrate how complex reproductive success in space is, and the great need for further research throughout the early stages of development.”
Why gravity is important for reproduction
Previous studies have investigated how sperm move in space, but no one had tested the ability of sperm to navigate the reproductive pathway under such controlled conditions.
The survey results are communication biology.
The research was carried out in collaboration with the University of Adelaide’s Andy Thomas Center for Space Resources, which focuses on the challenges of long-term space exploration and life beyond Earth.
Associate Professor John Culton, director of the Andy Thomas Space Resource Center, said: “As we move closer to species traveling through space and living on multiple planets, it is important to understand how microgravity affects the early stages of reproduction.”
Future research on reproduction in space
The next stage of the research will examine how different gravitational environments, such as the Moon, Mars, and artificial gravity systems, affect sperm navigation and early embryo development.
A key question is whether these effects change gradually as gravity decreases, or whether there is a threshold where changes occur suddenly and an “all-or-nothing” response occurs.
Answering this question will be essential for planning human reproduction on future settlements on the Moon and Mars, and for designing artificial gravity systems that support healthy development.
“Our latest research shows that many healthy embryos were still able to form when fertilized under these conditions. This gives us hope that reproduction in space may one day be possible,” said Dr. MacPherson.
