Hormones Matter TM

The need for thyroid testing during pregnancy

February 21, 2012  |  Staff


One in five women of reproductive age suffer from some form of thyroid dysfunction, mostly hypothyroidism (Gharib et al. 2005; Hollowell et al. 2002). In adult women, 95% of clinical hypothyroidism results from primary disease of the thyroid gland, generally, the autoimmune condition Hashimoto thyroiditis (Wartofsky et al., 2006). Autoimmune thyroid disease is also common among women with Type 1 diabetes mellitus, Sjogren syndrome, Addison disease, or pernicious anemia. Up to 25% of patients with Type 1 diabetes will develop postpartum thyroid disease (Alvarez-Marfany et al., 1994).

But what happens when someone with untreated thyroid disease gets pregnant? Depending upon the diagnostic criteria, hypothyroidism affects 0.3% (Casey & Leveno, 2006) to 5% (Gharib et al. 2005) of pregnancies. The symptoms are vague and are similar to other pregnancy concerns making diagnoses based on clinical symptoms alone difficult. Hypothyroid symptoms include fatigue, constipation, cold intolerance, muscle cramps, insomnia, weight gain, carpal tunnel syndrome, hair loss, voice changes, and slowed thinking.

The consequences of undiagnosed hypothyroidism during pregnancy are significant. Hypothyroidism is associated with premature birth, pre-eclampsia, abruption, low birth weight (LBW), postpartum hemorrhage, and impaired neuropsychological development in childhood (Burman, 2009). Research found that fetal loss was higher in untreated hypothyroid women (29%) vs hypothyroid women taking levothyroxine (6%), highlighting the need for early detection (Hallengren 2009).

Hyperthyroidism, the result of an excess of thyroid hormones, complicates less than 1% of pregnancies (ACOG Practice Bulletin, 2002). Symptoms of hyperthyroidism are uncommon in normal pregnancy and thus somewhat easier to identify clinically. Maternal symptoms include weight loss or failed weight gain despite increased dietary intake, resting tachycardia, hypertension, tremor, eye stare, eyelid lag, proptosis, and thyroid enlargement or nodule.

Graves’ disease, an autoimmune disorder occurring in 0.5% of the population, accounts for more than 90% of the hyperthyroidism associated with pregnancy. Complications associated with undiagnosed or poorly managed hyperthyroidism during pregnancy include pre-term labor, pre-eclampsia and maternal thyroid storm, fetal tachycardia, low birth weight, congenital abnormalities and stillbirth.

For pregnant women, there is little consensus among the major medical associations regarding who, when and how to test for thyroid function during pregnancy. It is argued that by the time TSH (the gold-standard in thyroid diagnostics) becomes hyper-elevated and the clinical symptoms emerge, the damage to fetal neuro development related to insufficient maternal T4 stores, has already been done (Calvo et al. 2002).  Evidence is emerging however, that maternal T4 levels may not track directly with elevated TSH levels especially in the first trimester when the demands for maternal T4 are greatest (Morreale de Escobar et al. 2000).

Given the dire consequences of untreated thyroid dysfunction during pregnancy, there is a need for more accurate, non-invasive and less expensive thyroid function tests with reference ranges specifically identified for this population of women. Screening for thyroid function in women of reproductive age and in pregnant women could reduce maternal and fetal complications.