What is Thyroid Gland?

Thyroid Gland is a small ductless butterfly shaped gland located at the base of neck, below the voice box.

The thyroid secrets hormones, and releases them directly into the blood, regulating growth and development by controlling the rate of metabolism.

What are The Functions of Thyroid Hormones?

Thyroid gland is made of follicles that produces and stores thyroid hormones: thyroxin (T4) and tri iodothyronine (T3). These hormones are stored in the follicles as colloid. These hormones play a important role in many fundamental processes including cell differentiation, growth, temperature regulation and basal metabolic rate. T3 and T4 regulate your body’s temperature, metabolism and heart rate. The thyroid gland is controlled by another hormone called thyroid stimulating gland hormone (TSH). TSH is produced by pituitary gland in your brain.

The TSH release is regulated by  positive and negative feedback of Thyrotrophin Releasing Hormone (TRH)  released by the hypothalamus. Any disruption in the regulation of thyroid stimulating factors can result in either lower production of thyroid hormones (Hypothyroidism) or higher production of thyroid hormones (Hyperthyroidism).

Thyroid hormones play an important part in growth and  are critical in pregnancy. If the thyroid is over or underactive, this can affect ovulation and reduce fertility. Many women suffer from thyroid dysfunction; around 25% of women in their lifetime, which is around 4 times higher than men.

Graves disease is the most common thyroid dysfunction, affecting 1% of the population. These conditions are important in fertility, because thyroid hormones are important in regulating ovulation, preventing miscarriage and aiding fetal brain development.

Goiters and Nodular Thyroid Disease

Goiter refers to an enlarged thyroid gland. It is caused by Iodine deficiency in the diet, or an auto immune disease (Hashimoto); or nodular disease.

In Iodine deficient areas, thyroid enlargement is due to compensatory effort to produce enough thyroid hormone.

There are endemic regions of iodine deficiency, or environmental goiterogens like Cassava roots, vegetables like cabbage and cauliflower.  Most goiters are asymptomatic.

Thyroid function tests should be performed to exclude hypothyroidism or thyrotoxicosis.

Role of  Thyroid Gland in Infertility?

The thyroid has been  overlooked in fertility treatment, unless results are very abnormal. However, there are clinicians who believe that it should be taken much more seriously than it currently is. There is evidence that actually thyroid hormones play a big part in fertility and pregnancy.

The Thyroid Gland Function Affects Fertility in Both Men and Women.

Thyroid hormone levels:

Recent studies have suggested that TSH should be no higher than 2.5 when trying to conceive and 3.0 during pregnancy. If TSH or iodine levels are too high/low, this can be easily rectified with supplementary medication.

Hyperthyroidism: Hyperthyroidism is when the thyroid is overactive and produces more than normal amounts of thyroid hormones. Graves disease and other autoimmune diseases are the most common manifestations of this.

Hyperthyroidism Affects  Fertility in Women?

Hyperthyroidism may be characterized by infrequent scanty menstruation or amenorrhea. Thyrotoxicosis (usually from Graves’ disease/gestational transient thyrotoxicosis) increases the risk of spontaneous abortions and especially if on methimazole, there is an amplified risk of congenital anomalies and Aplasia Cutis.  The presence of hyperthyroidism can be measured by performing a TSH blood test. Hyperthyroidism can cause infrequent periods in women and low sperm counts in men.

Treatment: Once hyperthyroidism is diagnosed it should be treated with medication, radioactive iodine or surgery.

After Treatment Hormone Levels Generally Return to Normal.

Hypothyroidism: Hypothyroidism occurs when the thyroid is underactive and does not produce enough thyroid hormones. This is often caused by a lack of iodine in the diet, or by autoimmune diseases such as Hashimoto’s thyroiditis. It is associated with reduced fertility, an increased risk of miscarriage, lower infant intelligence, pre-eclampsia, premature birth and infant death.

This  decrease in thyroid secretions affects the synthesis of factors VII, VIII, IX, and XI and estrogen break through bleeding secondary to anovulation, which may explain the frequent, prolonged, and heavy menstruation. This irregular ovulation and disruption of break through bleeding result in irregular cycles which in most cases is the cause of infertility. Hypothyroidism also affects the incidence of miscarriage in women. More than half of hypothyroid patients have menstrual irregularities and one third of sub fertile patients have thyroid disease.

Thyroid hormones are vital for the production of both Estradiol and progesterone lack of which may cause infertility. Hypothyroidism can be diagnosed by a blood test and can be easily treated.

Treatment:  is usually supplementation with iodine or a synthetic form of thyroid hormone, thyroxin.

Thyroid Antibodies

Apart from thyroid hormone level; thyroid antibodies are another factor which has an impact on fertility. These are produced if the thyroid is being mistakenly attacked by the immune system as part of an auto-immune disease, and they are present in between 8 and 30% of infertile women. Thyroid antibodies increase the risk of pregnancy loss by four  times. The mechanism of this is not yet clear; it could affect implantation or interact with other antibodies. Again, the best way to pick up on this is to undergo a blood test, so that appropriate treatment can be arranged if necessary.

Conclusion

Thyroid gland secretions are involved in all aspects of reproduction. Altered thyroid hormone levels are associated with

• Disturbed folliculogenesis,
• Lower fertilization rate,
• Lower embryo quality.
• Lower pregnancy rates.

Therefore, screening for thyroid function and autoimmunity should be performed as part of the work-up of women with sub fertility or miscarriage. L-thyroxin should be administered when Sub clinical hypothyroidism  is present in women of childbearing age if they plan a pregnancy, in order to improve the likelihood of successful pregnancy outcomes.

Moreover, women of childbearing age who plan to undergo fertility treatment should get their thyroid investigated.

Preventative Measures

Apart from diagnosis and medication, there are some lifestyle choices that can be taken to ensure that the thyroid functions properly. Reducing stress is important, as high cortisol (a stress hormone) levels inhibit thyroid hormone production. Ovarian ,Adrenal and Thyroid (OAT) axis plays an important role in ovarian function. Production of thyroid hormones increases the sensitivity of the tissues to these hormones. Modern diets also play a large part in thyroid dysfunction, in particular refined grains, sugars, soy products, peanuts and caffeine. Eating a healthy diet and avoiding smoking and alcohol consumption are therefore recommended.