Introduction: Thyroid dysfunction in pregnancy is not uncommon (1). Early recognition and intervention are essential to avoid any adverse pregnancy outcomes however caution must be exercised while interpreting the thyroid functions during pregnancy to avoid any unnecessary treatment.
Case report: 32-year female with was referred to the combined antenatal clinic for review following an abnormal thyroid function tests during pregnancy. She had no known medical conditions and was on no regular prescribed or over the counter medications. She had a routine blood test at the GP surgery at around 8 weeks of gestation, which showed thyrotoxicosis. There was no history of recent acute illness or use of iodine contrast medium. There was no family history of thyroid dysfunction. On clinical examination, she had a mild goitre. There were no other clinical signs of hyperthyroidism and no signs of thyroid eye disease. The TSH receptor antibody tested at 8-weeks of gestation was negative (<0.3 IU/l, range 0 - 0.9). She reported ongoing emesis from the first trimester of pregnancy, which continued during the second trimester, but was settling as the pregnancy was advancing. The thyroid hormone levels normalised as the pregnancy advanced without any intervention. The thyroid hormone profile done at various times of gestation was as follows:
|TSH||Free t4||Free t3|
Conclusion: It is important to identify the transient gestational thyrotoxicosis to avoid any unnecessary treatment of abnormal thyroid functions (2). Due to the weak thyroid stimulating activity of the beta HCG (human chorionic gonadotrophin) and direct stimulation of the maternal thyroid gland by HCG, changes in thyroid functions including a low or undetectable TSH and rise in total and free t4 are not uncommon. We do not advise treating an isolated low TSH or elevated free T4 in the absence of clinical evidence of hyperthyroidism, as with our patient whose thyroid function was monitored during her pregnancy but no treatment was required.
1. Führer D, Mann K, Feldkamp J, Krude H, Spitzweg C, Kratzsch J, et al. Schilddrüsenfunktionsstörungen in der Schwangerschaft. DMW - Deutsche Medizinische Wochenschrift. 2014 Oct 7;139(42):214852.
2. Albaar MT, Adam JMF. Gestational transient thyrotoxicosis. Acta Med Indones. 2009 Apr;41(2):99104.