title: Biology of fertility control by periodic abstinence. Report of a WHO scientific group.
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D003267:Contraception; D005260:Female; D005298:Fertility / Q000502:physiology*; D006801:Humans; D008297:Male; D008598:Menstruation / Q000502:physiology*; D008875:Middle Aged; D010060:Ovulation