Microgravity reduces the ability of sperm to navigate reproductive tracts

Having a baby in space may require a bit more direction, with new Adelaide University research revealing the navigational abilities of sperm are negatively impacted by a lack of gravity. 

Researchers at the University's Robinson Research Institute, School of Biomedicine and Freemasons Centre for Male Health and Wellbeing investigated how extraterrestrial conditions might influence sperm navigation, fertilisation and early embryo development. 

Sperm samples from three different mammals, including humans, were put through a 3D clinostat machine, developed by Dr Giles Kirby at Firefly Biotech, which simulates the zero gravity conditions experienced in space by flipping cells, so they become disorientated. The sperm then travelled through a maze designed to mimic the female reproductive tract. 

This is the first time we have been able to show that gravity is an important factor in sperm's ability to navigate through a channel like the reproductive tract."

Dr. Nicole McPherson, senior author, Adelaide University's Robinson Research Institute

"We observed a significant reduction in the number of sperm that were able to successfully find their way through the chamber maze in microgravity conditions compared to normal gravity. 

"This was experienced right across all models, despite no changes to the way sperm physically move. This indicates that their loss of direction was not due to a change in motility but other elements." 

The addition of the sex hormone progesterone, which is important for pregnancy establishment, helped more human sperm to overcome the negative effects that simulated microgravity had on navigation. 

"We believe this is because progesterone is also released from the egg and can help guide sperm to the site of fertilisation, but this warrants further exploration as a potential solution," said Dr McPherson. 

Researchers also looked at the impact that exposure to microgravity during fertilization had on embryo development in animal models. 

They observed a 30 per cent reduction in the number of mouse eggs that were successfully fertilised after four hours of exposure to zero gravity, compared to typical conditions on earth. 

"We observed reduced fertilisation rates during four-to-six hours of exposure to microgravity. Prolonged exposure appeared to be even more detrimental, resulting in development delays and, in some cases, reduced cells that go on to form the fetus in the earliest stages of embryo formation," said Dr McPherson. 

"These insights show how complex reproductive success in space is and the critical need for more research across all early stages of development." 

While previous studies have looked at sperm motility in space, to date none have assessed sperm's ability to navigate through a reproductive channel under these controlled conditions. 

The results of this study have been published in Communications Biology (Nature Portfolio). 

The work is also a collaboration with Adelaide University's Andy Thomas Centre for Space Resources, which focuses on addressing the challenges of long-term planetary exploration and living in off-Earth environments. 

"As we progress toward becoming a spacefaring or multi-planetary species, understanding how microgravity affects the earliest stages of reproduction is critical," said Associate Professor John Culton, Director of the Andy Thomas Centre for Space Resources. 

Researchers are now entering the next phase of their investigation into how varying gravitational environments, such as those on the Moon, Mars and proposed artificial gravity systems impact sperm navigation and early embryo development. 

A key question is whether gravity-related changes in development occur gradually as gravitational force decreases, or if there is a threshold effect, an "all or nothing" response. 

Understanding this distinction is essential for planning future human reproduction in extraterrestrial environments, including Moon and Mars settlements, and for designing artificial gravity systems that support healthy development. 

"In our most recent study, many healthy embryos were still able to form even when fertilized under these conditions. This gives us hope that reproducing in space may one day be possible," said Dr McPherson.