Gestational hypothyroidism: development of mild hypothyroidism in early pregnancy in previously euthyroid women.

OBJECTIVE

To determine the proportion of euthyroid women attending a fertility practice who develop hypothyroidism in very early pregnancy (gestational hypothyroidism [GHT]), and to examine the association of GHT with exogenous gonadotropin treatment.

DESIGN

Retrospective cohort study.

SETTING

A private reproductive medicine practice.

PATIENT(S): All healthy women (N = 94) with infertility or recurrent pregnancy loss, TSH level <2.5 mIU/L, negative thyroid peroxidase antibodies at initial evaluation, and not taking thyroid medication, who conceived during an 18-month period.

INTERVENTION(S): Usual fertility care; 30 women who had received exogenous gonadotropins.

MAIN OUTCOME MEASURE(S): Serum TSH level at the time of pregnancy detection.

RESULT(S): Gestational hypothyroidism (TSH ≥ 2.5 mIU/L) developed in 23 of 94 women (24%). The mean increase in serum TSH level from initial evaluation to early pregnancy was 0.45 ± 0.08 [SE] mIU/L. There was a trend toward the association of GHT with use of exogenous gonadotropins. Gestational hypothyroidism was positively associated with initial prepregnancy TSH level.

CONCLUSION(S): Euthyroid women may develop mild hypothyroidism in early pregnancy, especially after exogenous gonadotropin treatment. Appropriate vigilance will allow for timely levothyroxine treatment.