I like the gross idea and concept, and the great art and animation. My main concern is that it is too repetitive; by that I mean when the blood drops sing. Like another user said, it became annoying quickly. Instead of them singing a loop with perfect synchronization, why not elaborate more with a full song about periods or something to make it more interesting?
By the way, I actually watched more than "3 months later" hoping for some sperm to access the uterus :P