Thyroid Disorders and Diabetes

Pregnancy, diabetes, and thyroid disorder
Pregnancy-related thyroid dysfunction is three times more common in women with diabetes and should be anticipated in every pregnant woman with Type 1 diabetes. Postpartum thyroiditis may cause fluctuating thyroid hormone levels in the months following delivery. In addition to symptoms such as fatigue, depression (the “baby blues”), irritability, and heart palpitations, blood glucose control and insulin requirements may be affected during this period of thyroid dysfunction and profound reproductive hormonal changes. Continued monitoring of thyroid function is necessary in all women who experience postpartum thyroiditis, since roughly one-third will develop permanent hypothyroidism within three to four years and will require thyroxine replacement.

Women who have diagnosed hypothyroidism and already take thyroxine before pregnancy often need to increase the dose of thyroxine during pregnancy. Adequate thyroxine replacement is vital for the baby’s neurological development. Women with active Graves disease may enter a period of remission during pregnancy, when the disease becomes less active, but they can expect a recurrence following delivery.

If hyperthyroidism is poorly controlled during pregnancy, the risk of maternal complications such as preeclampsia (a serious condition characterized by high blood pressure) and fetal problems such as prematurity increases. The maintenance of normal thyroid function and tight blood glucose control is therefore of utmost importance during pregnancy to ensure a successful outcome.

Diagnosis of thyroid disorder
As mentioned earlier, the diagnosis of abnormal thyroid function based solely on symptoms can be difficult. In people with diabetes, it may be even more difficult because of the complex interrelationships of thyroid function and diabetes. Both chronically high blood glucose and hyperthyroidism can cause weight loss despite good appetite, weakness, and fatigue. Likewise, severe diabetic kidney disease can produce symptoms such as swelling, weight gain, and hypertension, which may be confused with hypothyroidism.

The most reliable method used to diagnose thyroid disease is the simple, relatively inexpensive, yet highly sensitive TSH blood test. This test measures directly the amount of TSH produced by the pituitary gland. Since the pituitary is the first organ to recognize abnormal thyroid function, testing its function is the most sensitive way to monitor thyroid function. In addition to diagnosis, the TSH test is also used to monitor and adjust the dosage of thyroxine therapy.

Before the introduction of the TSH test in the late 1960’s, blood tests for thyroid function measured only the levels of the thyroid hormones, T3 and T4. However, these hormone levels can appear relatively normal even when the thyroid is not functioning normally, because the pituitary gland will compensate for thyroid dysfunction. When the thyroid starts to fail (a sign of early hypothyroidism), the pituitary responds by producing higher levels of TSH to stimulate the thyroid to produce more thyroid hormones, thereby maintaining normal circulating T3 and T4 levels. Conversely, when the thyroid gland produces too much thyroid hormone (a sign of early hyperthyroidism), the pituitary responds by producing less TSH, thereby reducing T3 and T4 production from the thyroid.
Therefore, prior to any changes in the thyroid hormone levels, there is a detectable change in the TSH level, which indicates abnormal thyroid function. A normal TSH level ranges from 0.4 mU/ml to 4.0 mU/ml (microunits per milliliter). A below-normal TSH level indicates hyperthyroidism, and an above-normal TSH level indicates hypothyroidism.