“Sex is very difficult in zero gravity, apparently, because you have no traction and you keep bumping against the walls,” biologist Athena Andreadis of the University of Massachusetts Medical School told SPACE.com in 2011. “Think about it: you have no friction, you have no resistance.”

In addition to the mechanical difficulties of completing the act, actually conceiving and delivering a child in space could be “downright dangerous,” SPACE.com reports.

“There are many risks to conception in low or microgravity, such as ectopic pregnancy,” said Laura Woodmansee, author of the book “Sex in Space” (Collector’s Guide Publishing, Inc., 2006). “And, without the protection of the Earth’s atmosphere, the higher radiation levels raise the probability of birth defects.”