Hashimoto’s thyroiditis is the most common disease which causes a decreased thyroid gland function (hypothyroidism) in women during reproductive period. Basically, hypothyroidism leads to less energy consumption in the body. Therefore, hypothyroidism causes weight gain and difficulty in losing weight. Additionally, hypothyroidism results in oligo-anovulation which is presented by long lasting and increased amount of menstrual bleeding.

The investigation of thyroid gland is important in diagnosis of polycystic ovary syndrome.Both hypothyroidism and polycystic ovary syndrome may be seen together in a woman. Usually, decreased energy consumption ,which leads to weight gain and obesity, causes presentation of  symptoms and signs of women with  polycystic ovary syndrome.

Hypothyrodism also causes a decrese in production of shbg (sex hormone binding globulin), transport protein of male hormones (androgens), by liver. That’s why, thyroid function tests should be investigated in women who have androgens in normal limits, although have the symptoms and signs of polycystic ovary syndrome.

Graves disease is the common disorder which increases the thyroid gland function (hyperthyroidism). Particularly, these women are not obese and have a difficulty in gaining weight. But, they may have long lasting and less amount of menstrual bleeding usually presenting spotting.