PMC8322681_01
Time course of serum levels of hCG ( ), TSH ( ), fT4 ( ) and fT3 ( ). FLC performed in the setting of TTTS led to resolution of hyperthyroidism within 1 week along with a rapid decrease in hCG levels. Hormones were measured by ECLIA (electrochemiluminescence immunoassay) on cobas e602 (Roche Diagnostics, Rotkreuz, Switzerland). Reference ranges (not trimester-specific): TSH, 0.270-4.20 mUI/l; fT4, 12-22 pmol/l; fT3, 3.1-6.8 pmol/l.
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Further investigations revealed overt hyperthyroidism ( Figure 1 ). The unexplained persistence of tachycardia (up to 120 bpm) 24 hours after FLC prompted thyroid function tests that showed overt hyperthyroidism ( Figure 1 ); TPOAb and TRAb were again negative and thyroid ultrasonography was still normal. Both thyroid function tests and hCG plasma levels before FLC were retrospectively assessed on a stored plasma sample obtained at 16 WG and were clearly consistent with a relapse of overt thyrotoxicosis along with a substantial increase of hCG plasma level ( Figure 1 ).