Hypothyroidism in pregnancy; implications of the 2016 updated guidelines for the Monash Health Endocrine in pregnancy clinic.

Abstract

Background: Pregnancy has a significant impact on the thyroid gland with alterations in thyroid stimulating hormone (TSH) and thyroid hormone levels. New guidelines proposed by the American Thyroid Association1 suggest that thyroxine replacement is not required in pregnant women with TSH <4mIU/L, and negative thyroid peroxidase (TPO) and thyroglobulin (Tg) autoantibodies. Aim(s): 1. To assess the range of TSH values and autoantibody status of women with newly diagnosed hypothyroidism in pregnancy 2. To identify the proportion of women in whom thyroxine treatment will no longer be recommended Methods An audit of women reviewed in the Monash Health Endocrine in Pregnancy Clinic between March 2012 and December 2015 was performed. Data collected included gestational history, plurality of pregnancy, past history of thyroid disease, thyroid function tests (TFTs) and antibody status. Result(s): Two hundred and eighty-nine women were reviewed for hypothyroidism; 148 (51.2%) of these women were newly diagnosed with hypothyroidism in pregnancy, currently defined by TSH > 2.5 mIU/L in the first trimester, with a mean gestation at first TFTs of 10.8 weeks. All were confirmed singleton pregnancies. Amongst these women, 49 (33.1%) had an initial TSH measurement of 2.5-4.0mIU/L, 80 (54.1%) had a TSH of 4.1-9.99 mIU/L and 19 (12.8%) had a TSH >= 10.0 mIU. Of those with TSH values of 2.5-4.0 mIU/L, 17 (35%) were identified as positive for either TPO or Tg antibodies, 26 (53%) were both TPO and Tg antibody negative with the remaining 6 patients' antibody status unknown. Conclusion(s): New guidelines proposed by the American Thyroid Association suggest that thyroxine during pregnancy is not required in women with a TSH <4 mIU/L and negative thyroid autoantibodies. Based on these recommendations, approximately 20% of women overall, but 50% of those with TSH 2.5-4.0 mIU/L, currently referred to our service may not require thyroxine or specialist Endocrinologist review during pregnancy.