14th February 2014 | by MFC Team
I’m 32 years old and have been trying to conceive for over 8 months. My doctor has done a number of basic tests including TSH, T3 and T4, iron, etc. and says everything looks normal except my TSH levels which are a bit high at 2.98 mU/L. Could you please help me understand the relationship between thyroid levels and pregnancy?
Written by our medical expert Dr. Stephen Hudson, Director of the Victoria Fertility Centre in British Columbia, Canada.
We should start with some background information on the thyroid gland. The gland is located in the neck close to the voice box (larynx). Its role is to release thyroid hormone (called T4 or thyroxine), which controls the body’s metabolic rate. The thyroid gland is regulated by the pituitary gland, which in turn is regulated by the hypothalamus. If the T4 level is low – the pituitary gland releases TSH (thyroid stimulating hormone) which increases the amount of T4 released by the thyroid gland. This regulatory process is called a “feedback loop” and is common in the human body.
If there is too much thyroid hormone being released, it causes the medical condition of hyperthyroidism. In such a condition, blood tests will show a high T4 level and a low TSH. High thyroid hormones speed up the metabolic rate, causing symptoms such as a fast pulse rate, sweating, diarrhea, and anxiety.
On the other hand, if there is too little thyroid hormone being released, the condition is called hypothyroidism. Blood tests will show a low level of T4, and high levels of TSH. In this case the pituitary gland is trying to get the thyroid to release more T4. Symptoms of low thyroid hormones include hair loss, exhaustion, depression, and cold intolerance. Menstrual irregularities and fertility problems are also common in cases of hypothyroidism.
The ideal TSH is a matter of much debate and controversial. Ideally TSH should be kept below 2.5 mU/L while trying to conceive and during the first trimester of pregnancy, to facilitate pregnancy and ensure normal fetal brain development. TSH levels should ideally be below 3.0 mU/L during the 2nd and 3rd trimesters.
Sometimes the immune system attacks the thyroid gland by producing anti thyroid antibodies (ATA) that damage the thyroid gland and affect thyroid function. Approximately 10% of women are found to have elevated levels of ATA. The presence of ATA has been associated with fertility problems including miscarriage, premature ovarian failure, unexplained infertility, endometriosis, polycystic ovarian syndrome, and recurrent IVF failures. Elevated levels of ATA are usually treated with Thyroxine (T4) to keep the TSH below 2.5 mU/L.
My own advice is that all women experiencing any form of reproductive difficulties should have a TSH and testing for ATA. Your doctor has already tested your TSH. I’d encourage you to ask your doctor to also conduct a test for ATA. With these results, your doctor will have the necessary information to guide you on how best to achieve a healthy pregnancy.
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