# during the reproductive years there are five main factors that will influence the fluctuations in oestrogen and progesterone > During the reproductive years there are five main factors that will influence the fluctuations in oestrogen and progesterone: i) fluctuations across the eumenor- rheic menstrual cycle; ii) disruptions to the eumenorrheic menstrual cycle caused by illness or disease (e.g., polycys- tic ovary syndrome, endometriosis or other hypothalamic pituitary axis disruptions), low energy availability, the first two years after menses, and the time nearing menopause; iii) manipulation of the eumenorrheic menstrual cycle with exogenous hormones, both synthetic and natural (e.g., HC and HRT); iv) pregnancy (increasing ovarian steroids profile); and v) menopause (decreasing ovarian steroid profile). Researchers should strive to adopt all recommendations that are appropriate, thus facilitating good practice in this are[[(Elliott-Sale et al., 2021)#^h5yva]]