Gestational hyperthyroidism in women from mild to moderate iodine deficiency (ID) areas
S. Presti, M. Moleti, B. Di Bella, G. Sturniolo, F. Di Mauro, F. Trimarchi & F. Vermiglio
Graves disease (GD) and gestational transient thyrotoxicosis (GTT) are the main causes of hyperthyroidism in pregnancy, their prevalence ranging between 0.10.4% and 0.311%, respectively.
Aim of the study: To evaluate both prevalence and outcome of gestational hyperthyroidism in mild to moderate ID areas.
Subjects and methods: 482 consecutive pregnant women who had never undergone thyroid function evaluation before and enrolled within 13 wks of gestation. Serum FT3, FT4, TSH levels were measured every 6 wks up to pregnancy term, while anti-TPO antibodies at enrollment only. Anti-TSH receptor antibodies (TRAb) were tested when TSH was below the lower limit of the trimester-specific reference range (1st 0.03 mU/L; 2nd and 3rd 0.3 mU/L).
Results: Thirty-two/482 (6.6%) pregnant women had serum TSH values <0.03 mU/L at first sampling. Of these, 17/32 (53.1%) were overtly hyperthyroid, and 15/32 (46.9%) had subclinical hyperthyroidism. TRAb assay revealed the autoimmune origin of hyperthyroidism in 6/32 (18.7%) women. Of the remaining 26/32 (81.2%) TRAb-negative women, 12/26 (46.1%) were diagnosed with GTT and 14/26 (53.8%) showed isolated hypothyrotropinemia. Of the 6 GD women, 1/6 spontaneously recovered from hyperthyroidism at early 2nd trimester, whereas 2/6 were given anti-thyroid drugs, and 3/6 showed FT4 levels that were consistently at the upper normal limit for general population. TRAb titer decreased of 3382% over gestation in 4/6, and became undetectable in the remaining 2/6 GD women. Of the 12 GTT women, 1/12 miscarried at early gestation. In the remaining 11/12, spontaneous remission of hyperthyroidism occurred, mostly within the 20th week.
Conclusion: The high prevalence of autoimmune hyperthyroidism (6/482, 1.2%), occasionally found in pregnancy, represents a further reason for recommending systematic and early thyroid function testing in pregnant women.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector