Causes of low thyroid
No matter what the cause, the effects of low thyroid (known clinically as hypothyroidism) are the same for everyone. But identifying the cause in your specific case is important for further treatment by a medical professional. Causes of low thyroid hormone include radiation treatment for cancer; complete or partial thyroid gland removal; an inherited condition; a non-functioning pituitary gland; pregnancy or recent delivery of a baby; or Hashimoto's thyroiditis, an immune disease.
How thyroid hormones are affected
The thyroid's main function is to convert iodine into the hormones triiodothyronine (T3) and thyroxine (T4), which regulate metabolism. In the case of hypothyroidism, the thyroid isn't making enough T3 and T4 to keep the body's metabolism at the correct level. In response to the low levels, a chain reaction starts. The hypothalamus begins producing thyrotropin-releasing hormone (TRH), which in turn signals the pituitary gland to secrete thyroid-stimulating hormone (TSH). TSH then prods the thyroid into increasing production of T3 and T4. A simple blood test to find the level of TSH produced by your body will tell you if you're hypothyroid: A high TSH level indicates that your thyroid is compromised and cannot keep up with its normal production of T3 and T4.
Symptoms of hypothyroidism
When your body does not make enough thyroid hormone (T3 and T4), it can cause a number of symptoms. There is no minimum number of symptoms needed for a diagnosis. At first, you may just feel sluggish and fatigued, but then you will start to notice other symptoms such as hair loss, sensitivity to cold, dry skin, brittle nails, memory problems, trouble concentrating, constipation, depression, mood swings, unexplained weight gain or hoarseness. You can also develop a goiter, which is a swelling of the thyroid gland caused by the gland's overexertion.
Hypothyroidism and pregnancy
Pregnant women who suffer from decreased thyroid function are at greater risk for miscarriage, particularly in the first few months of gestation. If you know your levels are low, notify your obstetrician and the physician who is treating you for the hypothyroid condition. Your TSH level can rise quickly in the first few months of pregnancy due to the increased production of estrogen, increasing the risk of miscarriage. This means you will either need to start on medication to lower your TSH level or increase your current dosage. Many guidelines state that pregnant women should have their TSH levels tested at least once per trimester to ensure proper treatment. Untreated, low thyroid also can cause premature labor and fetal abnormalities.