Many women don’t realise that good thyroid function is necessary for fertility, the ability to conceive and to maintain a pregnancy.  An under (or over) functioning thyroid can prevent you from achieving that much desired pregnancy. While there are many and varied reasons for infertility, suboptimal thyroid function may be that “missing link” especially for those with no specific reproductive problems.


A full thyroid evaluation is essential, and should be done as soon as possible for any woman who wants to get pregnant, especially if she:

  • Has been trying unsuccessfully to get pregnant for more than 6 months 
  • Has had two or more miscarriages 
  • Has an irregular menstrual cycle 
  • Has any family history of thyroid problems

What Does the Thyroid Gland Do?

The Thyroid gland is found in front of the trachea (air pipe) in the neck. Every cell in the body depends upon thyroid hormones for regulation of the body’s metabolism, blood calcium levels, energy production, fat metabolism, oxygen utilisation, balance of other hormones & weight maintenance. The thyroid gland releases hormones that circulate in the blood stream and are distributed to all the body tissues where they act as catalysts increasing oxidation processed in the tissue cells. The Thyroid gland releases 2 hormones T3 and T4. The release is stimulated by the hormone TSH, released from a gland in the brain. T3 and T4 regulate various enzymes controlling energy metabolism.

Thyroid antibodies are only found in people where somewhere along the line there has been thyroid cell injury. Raised thyroid antibodies cause the T3 and T4 to be less effective.

Healthy Thyroid function can be affected by:

  • Exposure to environmental toxins – electromagnetic radiation, chemicals, pesticides, heavy metals e.g. mercury & fluoride 
  • Genetic susceptibility 
  • High levels of stress 
  • Nutrient deficiencies 
  • Autoimmune disorders 
  • Infections 
  • Other hormone imbalances e.g. estrogen dominance, high prolactin levels

How Does Hypothyroidism (Low) affect fertility? 

  • Anovulatory cycles – not releasing an egg / ovulating.  This makes pregnancy impossible.
  • Luteal Phase Problems –With a short second half of the menstrual cycle a fertilised egg can’t implant securely and ends up leaving the body at the same time that menstruation would occur (very early miscarriage) & is often mistaken as a regular period.
  • High Prolactin Levels – due to elevated levels of Thyroid Releasing Hormone (TRH) and low levels of Thyroxine (T4) resulting in irregular ovulation or no ovulation.
  • Other Hormonal Imbalances – reduced sex hormone binding globulin (SHBG), oestrogen dominance, progesterone deficiency, all of which interfere with proper reproductive hormone balance.

Causes and Symptoms

  • An underactive thyroid gland is caused by insufficient release of the thyroid hormones into the blood stream, reducing the rate of energy production in the cells. The overall effect is tiredness, increased weight gain, the skin and hair deteriorates and most important from a fertility perspective the egg and uterine lining preparation and development are poor. Poor uterine preparation results in recurrent miscarriages. 
  • An overactive thyroid will speed up oxidation rate in the cells. Body temperature increases, there is profuse sweating, raised heart beat and respiration. The person becomes excitable and apprehensive and often the eyeballs protrude 


Medication (Eltroxin or Euthyrox) will boost the functioning of the thyroid gland. When the medication is administered a follow up thyroid test should be done to check medication dose is correct. Thyroid investigations and medication need to be overseen by a qualified endocrinologist.

It needs to be noted that both the thyroid gland and prolactin levels are influenced by stress. The stress factor should therefore be dealt with.

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