One may think that the microgravity in space would lead to "retrograde menstruation", a real condition where blood flows backwards into the pelvic cavity instead of out the body, according to the Mayo Clinic. You’ll be surprised to know that the female reproductive cycle actually is ONE of the systems in the human body that is just not impacted by being in space, whereas every other system within the body seems to be affected by being in a space-like environment!
Studies have shown that women can have periods as normally in space as they do on Earth. Menstrual blood flow isn’t affected by the weightlessness we experience in space, so it doesn’t float back in – the body is smart enough to know that it needs to get rid of it.
Of course, the human body goes through a lot of changes when in space. Not having gravity to constantly work against, it loses bone density and muscle mass. The cardiovascular system gets lazy and the body’s balance control mechanisms have to completely readopt themselves to find a new norm but one should be all aware of the huge difference between blood circulation and menstruation. If not, this is for you. The former is controlled by a network of arteries and veins that work all the time while the latter is controlled by hormones. The flow of menstrual blood isn’t guided by circulation of blood. So while male engineers were worried about retrograde bleeding, the female astronauts aren't worried at all, rather they expect a period in space to be the same as a period on Earth.
There is, however, another option for female astronauts and that’s not having periods at all, properly called medically induced amenorrhea. It makes possible to suppress menstruation by messing with the body’s natural hormones. The combined oral contraceptive pill is taken daily which contains an active ingredient that suppresses ovulation and thins the uterine lining. Taking the active pill for a full month, or many months, completely stops any bleeding, though there might be light spotting.
Another option is a hormonal intrauterine device (IUD) that achieves the same result through a localized release of low dose hormones. In some cases, like spaceflight, this could be a better option. Not only does an IUD negate the risk of missing a pill and getting a period, it’s small and inside the body. An astronaut could be in space for years, say, on a mission to Mars, and not have to think twice about menstruating. It would simply not be an issue. And a natural cycle of menstruation can be resumed once the IUD is removed.