Thyroid disorders can cause puberty and menstruation to occur abnormally early or late. In addition, abnormally high or low levels of thyroid hormone can cause very light or very heavy menstrual periods, very irregular menstrual periods, or absent menstrual periods (a condition called amenorrhea).

An overactive or underactive thyroid may also affect ovulation. This is the release of an egg for fertilization. Thyroid disorders may prevent ovulation from occurring at all. In addition, the ovaries are at an increased risk for cyst development if the woman has an underactive thyroid (hypothyroid). Severe hypothyroidism can actually cause milk production in the breast, while preventing ovulation.

Thyroid disorders during pregnancy can harm the fetus and may lead to thyroid problems in the mother after birth, such as postpartum thyroiditis. A deficiency of thyroid hormone can cause miscarriages, preterm delivery, stillbirth, and postpartum hemorrhage. Women with overactive thyroid during pregnancy are at risk of having more severe morning sickness. Ways of treating overactive thyroid gland during pregnancy must be individually considered.

Thyroid disorders may cause the early onset of menopause (before age 40 or in the early 40s).Some symptoms of overactive thyroid (hyperthyroidism) may also be mistaken for early menopause. These include lack of menstruation, hot flashes, inability to sleep (insomnia), and mood swings. Treating hyperthyroidism can sometimes ease symptoms of early menopause or prevent early menopause from happening.