Menstrual synchrony
Strassmann argued menstrual synchrony defined as menstruation overlap should be quite common. For example, the expected difference by chance between two women with 28-day cycles—which is approximately the average length of menstrual cycles of women at the age —is 7 days. Considering that the mean duration of menses is 5 days and the range is 2 to 7 days, the probability of menstruation overlap by chance should be high.
Functional hypothalamic amenorrhea
Females who have menstrual cycles lasting longer than 45 days and/or amenorrhea for three or more months should be evaluated for FHA. Differentiating FHA from the irregular menstrual patterns seen in adolescents during the initial years after menarche due to immaturity of the HPO axis can be challenging. However, studies have shown that even during this period, the length of a menstrual cycle does not exceed 45 days. Furthermore, healthy girls with normal BMI (18.5-25 kg/m) should develop regular menstrual cycles (every 28 +/- 3-5 days) within 1-2 years after menarche. FHA is a diagnosis of exclusion, and thus the evaluation should be used to rule out organic causes of amenorrhea (e.g., pregnancy, thyroid disorders, inflammatory bowel disease, etc.) Evaluation for FHA may include a thorough history and physical exam, laboratory testing, and imaging if appropriate. The Endocrine Society Clinical Practice Guidelines on Functional Hypothalamic Amenorrhea (FHA) suggests obtaining a baseline bone mineral density measurement by DEXA scan from any patient with 6 or more months of amenorrhea.