An underactive thyroid is known as hypothyroidism which is caused by decreased thyroid hormone production by the thyroid gland. The most common cause of hypothyroidism is Hashimoto’s disease (also known as Chronic Lymphocytic Thyroiditis, Hashimoto’s Syndrome, or Hashimoto’s Thyroiditis). Hypothyroidism can occur during pregnancy or worsen in pregnant patients who already have hypothyroidism. These reasons include the fetus increasing the metabolic demands of the mother and the mother experiencing changes in pregnancy that affect the thyroid gland.
Hypothyroidism is managed by supplementing the patient with oral thyroid hormone (levothyroxine, brand name Synthroid), even during pregnancy, but recent studies have shown that excess of this hormone can have devastating effects on both mother and child. Thus, it is important that the thyroid hormone levels should be kept at optimal levels. Unfortunately, even in normally pregnant women, thyroid hormone levels may vary, causing difficulty in diagnosing women who need treatment for hypothyroidism.
Fluctuations in thyroid hormone levels are normal during pregnancy
Hypothyroidism is diagnosed by elevated thyroid stimulating hormone (TSH) and decreased thyroid hormone levels. Sadly, TSH levels vary during pregnancy. TSH levels, even in normal women, decrease slightly in the first trimester of pregnancy and start to rise again in late 1st trimester. In the second trimester, TSH levels fall again and then rise slightly again at the end of the third trimester.
Therefore, these fluctuating TSH levels require a trimester-specific reference to be incorporated to prevent patients from being given thyroid hormone supplements when they are not needed.
Is it necessary to treat Subclinical Hypothyroidism in Pregnancy?
Hypothyroidism may be defined as “Symptomatic” if the patient is experiencing signs and symptoms associated with the condition. If these problems are absent then hypothyroidism is said to be “subclinical”.
Some doctors believe that pregnant women who have “subclinical hypothyroidism” should get treatment but studies have found no evidence to support the benefit of thyroid hormone replacement in subclinical hypothyroidism.
Approaches to the Management of Symptomatic Hypothyroidism in Pregnancy
Contrary to Subclinical hypothyroidism, symptoms of hypothyroidism in pregnancy can cause severe problems for the health of the mother and the baby. Thus, symptomatic hypothyroidism needs to be treated urgently.
It is important to consider trimester-specific TSH levels when determining the dose of thyroid hormone levels in hypothyroid pregnant patients. In addition to trimester-specific TSH levels, causes of hypothyroidism also affect thyroid hormone dosage. For example, pregnant women, where hypothyroidism is secondary treatment Grave disease and goiter, requiring the largest dose of thyroid hormone.
Pregnancy and Iodine
All pregnant and lactating women should receive adequate iodine intake to compensate for the increased loss of iodine in the urine and the mother’s iodine given to the baby. The best way to supplement with iodine is through the use of a multivitamin specifically developed for use by pregnant women.
The Role of Thyroid Peroxidase Antibodies (TPOAb) in Pregnancy
The most common cause of hypothyroidism is Hashimoto’s disease. Most patients with Hashimoto’s disease have TPOAb in their bloodstream. Women who have TPOAbs must have close monitoring for hypothyroidism during their pregnancy because they can develop Hashimoto’s Disease. Close monitoring is essential because TPOAbs can increase during pregnancy and, in itself, can increase the chance of developing hypothyroidism.
Sameer Ather MD, PhD is a Cardiologist based in Birmingham. He did his medical and PhD residency at Baylor College of Medicine, Houston, TX, and completed a cardiology fellowship at the University of Alabama, Birmingham, AL visit his website www.xpertdox.com.