Simulated microgravity alters sperm navigation, fertilization and embryo development in mammals.

As human space exploration extends toward long-duration missions and off-Earth settlements, understanding the impact of microgravity on reproduction is vital for sustaining life beyond Earth. This study investigates how simulated microgravity influences sperm navigation, fertilization, and subsequent early embryo development across three mammalian species; human, mouse, and pig, using a dual-axis 3D clinostat and clinically relevant in vitro culture systems. Sperm function was assessed via microchannels, revealing that microgravity impaired directional navigation and fertilization capacity in a time- and species-dependent manner. Fertilization still occurred, indicating compensatory mechanisms within subsets of sperm. Notably, progesterone partially restored navigation in human sperm under microgravity, suggesting the potential of chemical cues to mitigate gravitational absence. In vitro fertilization and embryo culture were performed under clinical assisted reproduction conditions, with time-lapse monitoring and blastocyst lineage characterization. Microgravity exposure during fertilization (4-6 h) compromised blastocyst development in pigs and led to elevated inner cell mass and epiblast counts in pig and mouse embryos. Prolonged exposure (24 h post-fertilization) resulted in developmental delays and reduced blastocyst cell numbers in mice. These findings underscore the resilience and vulnerability of reproductive processes under altered gravitational conditions, emphasizing the critical need to optimize peri-conception environments for successful reproduction for future space missions.