Hi dear I read carefully your question and understood your concern. Hyperthyroidism is a condition in which the thyroid gland is overactive and makes excessive amounts of thyroid hormone. Hyperthyroidism speeds up some of your body s processes. Light menstrual periods—sometimes even missed periods is a symptom of hyperthyroidism.So,your irregular cycle (absent menstruation)can be due to hyperthyroidism. But don t worry,if your thyroid function become normal,the symptoms of hyperthyroidism will gradually disappear and your periods will return to a normal monthly cycle and this will not affect your fertility in the future. Anyway,my advice is to meet your doctor and discuss with him the other causes of irregular periods like lifestyle factors ,contraceptive etc. At the other side the results of the pelvic ultrasound will give important information about other causes like:Polycystic ovary syndrome and Gynaecological problems. Hope I have answered your question.If you have any doubts then feel free to ask me.You can contact me at HealthCareMagic at my private link: bit.do/hcm-Dr-Xhardo.I will be happy to help. Thank you for using HCM. Wish you good health.