Transient subclinical hypothyroidism in early pregnancy.

In the present study, a new clinical state of transient subclinical hypothyroidism in 12 early pregnant women is documented. The incidence of transient subclinical hypothyroidism was 18 (0.19%) among 9,453 pregnant women examined in this series in Sapporo. The characteristics of transient subclinical early gestational hypothyroidism in our study may be summarized as follows: temporarily increased TSH in the blood (11.7 +/- 6.3 microU/ml; mean +/- S.D.) in early pregnant women at 8.5 +/- 2.4 weeks of gestation, accompanied with or without reduced FT4 which spontaneously return to normal at 17.9 +/- 7.1 weeks; no subjective complaints and no previous history of thyroid disease; small struma; positive titers of antimicrosome antibody and antithyroglobulin antibody; normal serum hCG; negative results for TSH receptor antibody. None of the infants show any physical abnormality such as struma and none of the patients had neck pain or fever suggesting subacute thyroiditis. The presence of autoantibody to the thyroid gland and echographical findings strongly suggest the existence of Hashimoto's thyroiditis in early pregnant women with transient subclinical hypothyroidism, although the cause of transient subclinical early gestational hypothyroidism remains obscure.