Thyroid and Fertility

Fertility is a sensitive subject for many women experiencing difficulties conceiving.  There are many factors that contribute to optimal fertility, one of which is the health of the thyroid gland.  In fact, low functioning thyroid (hypothyroid) is one of the leading causes of infertility; therefore, understanding the role and health of the thyroid gland is essential in the preparation for pregnancy.

The thyroid gland is a butterfly shaped gland that overlies the trachea or windpipe and is located at the base of the neck.  The primary role of the thyroid gland is to use iodine from food to produce thyroxine (T4), and small amounts of triiodothyronine (T3).  These hormones are released into the bloodstream to be circulated throughout the body.  T3 is the active form of the thyroid hormone; therefore, once inside the target cell, T4 is converted into T3.  The functions of thyroid hormones are numerous.  These functions include: regulation of metabolism, stimulation of carbohydrate, fat and protein metabolism, during pregnancy, fetal growth and development is stimulated by maternal thyroid hormone, with help from the fetal thyroid hormone later in pregnancy, and is required for activity of other hormones, like growth hormone, that influences heart rate, blood pressure and proper brain function (1).

Another function of the thyroid gland is its influence on the female reproductive hormones.  Thyroid hormone stimulates the proper production of follicle stimulating hormone (FSH) and luteinizing hormone (LH) from the brain.  FSH and LH are required for the maturation of the egg follicle and production of estrogen and progesterone at the level of the ovary. The proper balance of FSH and LH and subsequent estrogen and progesterone production, will stimulate the release of the egg at ovulation.  Research suggests that women with low functioning thyroids have decreased levels of FSH and LH (2).  Consequently, ovulation can be disrupted and infertility result.  The disruption in reproductive hormones as seen in women with thyroid disorders, often have menstrual cycle abnormalities such as scant or heavy flow and irregular cycles.  Although, thyroid function influences reproductive hormones, reproductive hormones also influence the function of the thyroid.  A high level of estrogen (estrogen dominance) reduces the thyroid function by increasing a protein called thyroid-binding globulin (TBG).  TBG binds and transports T4 and T3 hormones.  The catch is, once bound to the TBG, the thyroid hormones become inactive.  In a normal functioning thyroid, a subsequent increase in thyroid hormone compensates for this.  However, in someone with hypothyroidism, symptoms worsen, as there is less active thyroid hormone (3).

The adrenal gland is also a large player in the healthy function of the thyroid gland.  The adrenal glands are located on top of the kidney and produce cortisol, adrenaline and noradrenaline in response to stress.  Exposure to high levels of stress can increase the production of the stress hormones.  As a result, thyroid function is affected.  High levels of cortisol alter the production of thyroid hormone at the level of the thyroid gland and can prevent the conversion of T4 to active T3 at the level of the cell.   Continued high levels of stress can eventually lead to ‘adrenal fatigue’ or ‘insufficiency’ whereby the stress hormones become low.  This can also lead to a lower thyroid function.

Symptoms of hypothyroidism include:

• Difficulty losing weight
• Cold intolerance
• Low body temperature
• Constipation
• Dry skin
• Hair loss
• Depression or irritability
• Insomnia
• Poor concentration
• Brittle nails
• Decreased libido
• Fatigue
• Muscle cramps
• Menstrual cycle abnormalities
• Infertility
• Swollen thyroid (goiter)
• Slow pulse

Typically, testing thyroid function is limited to measuring only thyroid stimulating hormone (TSH), which is a hormone produced by the brain to stimulate the thyroid gland to produce T4.  In hypothyroidism, TSH will be high since more stimulation is required in a lower functioning gland. The problem with testing only TSH is that TSH can be within normal range while T4 and T3 are abnormal.  This scenario results when there are issues converting T4 to the active T3 hormonal at the level of the cell (see figure 1).  The most beneficial way to evaluate thyroid function, especially with fertility concerns, is to measure TSH, T4 and T3 levels.  Among experts in the field of thyroid health, a TSH level of 0.3-3.0 mlU/L is considered normal (4). With respect to fertility, research suggests a lower TSH (2.0 or below) is optimal if trying to conceive (5).

Getting the thyroid into shape for pregnancy requires support of the thyroid gland itself and the adrenal gland.  Providing the nutrients for optimal thyroid gland function include getting enough iodine and selenium.  Iodine is required for the production of thyroid hormones.  Dietary iodine requirements increase during pregnancy because there is a higher demand for T4 and T3 for fetal development.  Choosing a prenatal vitamin with an iodine content of 150-200μg per day can help achieve the required amount.

Selenium is another important nutrient required in the conversion of T4 to T3.  Eating foods rich in selenium, such as pumpkin seeds, Brazil nuts, and sunflower seeds, can help to prevent deficiency.

Adrenal support can be achieved through active stress relieving techniques like meditation, adequate sleep, taking time to do activities you enjoy, and avoiding processed foods and stimulates like coffee.  Herbal support can help improve adrenal and thyroid function.  Some herbs include Ashwagandha, Schisandra, Rhodiola, Licorice root, and Gotu Kola.

Evaluation of the thyroid function is essential for those women having difficulty conceiving. Ensuring proper nutrition through whole, nutrient dense foods, and nutrient and herbal supplements can help to balance the hormonal disruption caused by an underactive thyroid.

References

1. Helt, M. (Online) Every Woman’s Guide to Hypothyroidism and Fertility 2016
2. Acharya, N (2011) Gonadotropin levels in hypothyroid women of reproductive age group. J Obstet Gynaecol India. 61(5):550-3.
3. Arafah, BM (2001) Increased need for thyroixin in women with hypothyroidism during estrogen therapy. N Engl J Med. 344(23):1743-9.
4. Shomon, Mary J. (2006) The Thyroid Hormone Breakthrough. HarperCollins.
5. Stagnaro-Green, A et al (2011) Guidelines of the American Thryroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and Postpartum. Thyroid. 21(10):1081-1125.