The suggestion below: "There are third-party apps you can download and install that can be used to track your monthly cycle"... Remember the 3rd parties APPs does not work on galaxy watches.
So, please @Samsung do you have another solution?
It's incredible that a period tracker hasn't been implemented yet. I suggest that you postpone the development of a fully featured fertility tracker and include a basic tracker urgently, perhaps with the next update.
More than half of the population is female and more than half of females menstruate. And pretty much all of them track their period. It's an outrageous omission.
I don't mean to single Samsung out. Have a read of Invisible Women by Caroline Criado Perez to see how women's realities are overlooked throughout society.