menstrual blood vs menstrual flow

menstrual blood and menstrual flow both are nouns.

Word	Noun	Adjective	Verb	Adverb
menstrual blood	Yes	No	No	No
menstrual flow	Yes	No	No	No

As nouns, menstrual blood and menstrual flow are synonyms defined as:

menstrual blood and menstrual flow: flow of blood from the uterus; occurs at roughly monthly intervals during a woman's reproductive years

Other synonyms of menstrual blood include menorrhea.

menstrual blood (noun)	menstrual flow (noun)
flow of blood from the uterus; occurs at roughly monthly intervals during a woman's reproductive years	flow of blood from the uterus; occurs at roughly monthly intervals during a woman's reproductive years