8. Heavy Periods vs. Irregular Periods
Both overactive and underactive thyroid function can affect menstruation. With hypothyroidism, or low thyroid function, you may experience either heavy or irregular periods.
Your flow could be extremely heavy one month and missing the next. On the other hand, missed or unpredictable periods are more often associated with hyperthyroidism. Both conditions carry an increased risk of miscarriage and birth defects.