@fBoyle-- Well, you have to understand that throughout human history infant death was very common. Most children did not make it past their first year because of disease or poverty. So women gave birth often and I think our reproductive cycle is suited for this. It's to ensure the continuity of human life.
Just imagine if women menstruated once every three moths or perhaps twice a year. What would be the chances of her conceiving? It would be very slim and reproduction would slow down so much that population rates would quickly decrease.
It's actually a good thing that our menstrual cycle lasts one month. We are given a fresh new chance every month to have a baby. Our reproductive organs know exactly what to do and when to make conception possible.