Clinical presentation: A 34-year-old woman was referred for follow-up examination on 8th gestational week. She was known to have hypothyroidism for 2 years which was replaced by 50 microgram levothyroxine. Thyroid autoantibody levels were formerly elevated: aTPO 177 U/mL, anti-hTg 278 U/mL.

Palpation: no abnormality.

Hormonal investigation indicated euthyroidism with lower TSH-level 0.16 mIU/L, FT4 14.2 M/L.

Ultrasonography: the thyroids were echonormal. There were numerous hypoechogenic well-circumscribed small lesions partly presenting comet-tail artifact. The left lobe contained less hypoechogenic and less well-demarcated areas, as well. The former corresponded to insignificant lesions while the latter were signs of the underlying autoimmune thyroiditis.

Suggestion: we did not change the replacement dose because in the first trimester the TSH may decrease normally to 0.1 mIU/L. The THS was in the normal range later in the course of pregnancy, 2.01 mIU/L at 21st and 2.28 mIU/L at 33st week of gestation.