However, estrogen deficiency has been diagnosed in 13- or 14-years-olds who have just experienced their first period. Finally, someone with estrogen deficiency might be having irregular or skipped periods as a perimenopausal 35-plus-year-old. A teenager whose period has stopped has low estrogen levels; she is losing bone density and risks later life fractures. Because low progesterone levels (what could be called “progesterone deficiency”) always occur first. Thus, the term, “estrogen deficiency,” does not accurately and scientifically describe amenorrhea, oligomenorrhea, PCOS, perimenopause nor menopause.