Conversation so far:
which hormone stimulates the release of the ovum from the ovary
Leutinizing hormone, the other reproductive pituitary hormone, aids in egg maturation and provides the hormonal trigger to cause ovulation and the release of eggs from the ovary.
what is the most important hormone in the menstrual cycle
The most important hormone for reproduction is called gonadotropin releasing hormone, better known as GnRH.

Question: how come
Self-contained rewrite: how come gonadotropin releasing hormone is the most important hormone for the menstrual cycle