Problems with the thyroid gland or the hypothalamus can impact ovulation. One third of women experiencing fertility issues have thyroid complications. The thyroid gland is located in the neck; its normal function is to produce hormones that regulate metabolism and maintain normal development. Thyroid hormones play an indirect role in ovarian follicle growth. With insufficient follicular growth, the chances of an egg being released are diminished and with no egg, ovulation cannot occur.
An underactive thyroid results in insufficient thyroid hormone production. The condition is nearly 7 times more likely to affect women than men. In developing countries, hypothyroidism is most frequently caused by a dietary iodine deficiency; however, in countries with adequate dietary iodine, the predominant cause is Hashimoto’s thyroiditis, an autoimmune disease characterised by the immune system attacking the thyroid and resulting in inhibited thyroid hormone synthesis.
Symptoms of hypothyroidism include fatigue, weight gain, slowness in movements and thoughts, muscular aches and an increased sensitivity to cold. Between 20 and 50% of women with the condition will experience irregular menstrual cycles and/or hyperprolactinaemia. Hypothyroidism can also predispose a female to PCOS-like symptoms.
The first line treatment approach for hypothyroidism is synthetic thyroid replacement therapy (levothyroxine). For women who are suffering from irregular menstrual cycles due to low thyroid hormone, this treatment is often successful at restoring regular menstrual cycles. To date, the evidence regarding the use of levothyroxine during pregnancy is inconclusive; as such, women with hypothyroidism who fall pregnant should discuss with their doctor whether or not to continue taking their medication. In general it is considered that those women who have TSH levels greater than 4.0 mlU/L are at higher risk of miscarriage, so continued thyroid hormone replacement therapy will often be recommended to improve pregnancy rates.
Functional hypothalamic amenorrhoea (FHA)
Caused by a disruption in the secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus. This hormone would normally trigger the release of oestrogen from the ovaries, and a lack of it can therefore cause hypo-oestrogenism and anovulation. FHA disturbs the balance of the hypothalamic-pituitary-ovarian axis and is responsible for 20-35% of cases of secondary amenorrhoea. It can be one of the causes of delayed puberty.
Provided that a congenital condition has been ruled out, some of the most common causes of HPA are an imbalance in energy availability (often due to reduced calorie intake or excessive exercise) and stress. This means that making lifestyle changes and learning how to manage your emotional well-being can help to alleviate the symptoms of HPA. This is important because, left unmanaged, HPA can affect bone density, increase the risk of cardiovascular disease and predispose an individual to anxiety and depression.
There are other factors that might result in a woman failing to ovulate, or experiencing irregular ovulatory cycles. These include age, as the ovarian reserve diminishes over time, and lifestyle/environmental factors.