Funny enough, the first time the word “period” was uttered on TV (in the context of menstruation) was in a Tampax commercial in 1985, and Courteney Cox (from Friends among many other things) was the one who said it.
That was also the year that My Girl was released in theaters, and it showed the main character Vada getting her first period, so I guess that was a breakthrough year for it.
I believe the first film to portray menstrual blood on screen was Carrie from 1976.