Baseline demographic characteristics of the participants with and without occult POI.

The mean age, BMI, day of menstrual cycle at the time of blood sampling, and age at menarche were comparable between the participants with and without occult primary ovarian insufficiency (POI). The mean cycle length reported by the participants with occult POI were significantly shorter than those without it. Significantly higher number of participants with occult POI reported a positive family history of premature menopause in their mothers and/or sisters compared to those without occult POI.