menstrual flow vs menstrual blood

menstrual flow and menstrual blood both are nouns.

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

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

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

Other synonyms of menstrual flow include menorrhea.

menstrual flow (noun)	menstrual blood (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