menstrual hemorrhage
hypomenorrhea
http://purl.bioontology.org/ontology/MEDDRA/10021032
http://purl.bioontology.org/ontology/SNOMEDCT/64206003
http://purl.obolibrary.org/obo/NCIT_C34719
https://en.wikipedia.org/wiki/Hypomenorrhea
https://www.wikidata.org/wiki/Q5959912
Decreased menstrual blood flow.
Extremely light menstrual blood flow.
The Complete Dictionary of Sexology