# classifying the menstrual cycle into just 2 phases does not distinguish the multiple hormonal changes that occur within these 2 phases > eumenorrheic MC is separated into two distinct main phases, follicular and luteal, which are established on the occurrence of menstruation, follicular maturation, ovulation and corpus luteum formation. However, classifying the MC using just these two phases does not sufficiently distinguish the multiple hormonal milieus that occur within these two phases. Therefore, the MC is typically expressed in research using sub-phases, such as early follicular, late follicular, ovulatory, early luteal, mid luteal and late luteal.[[(Carmichael et al., 2021)#^g9vfm]]