The effect of infertility medication on thyroid function in hypothyroid women who conceive

To determine whether infertility medications alter thyroid status in patients with treated hypothyroidism, and whether resulting pregnancies require additional thyroid supplementation compared with those conceived spontaneously.

Prospective observational study of 18 infertility patients with treated hypothyroidism who conceived between July 2005 and July 2006 with or without infertility medications. Thyroid studies were performed prior to conception, at the time of pregnancy diagnosis, and approximately 6 weeks after an increase in thyroid replacement dose.

Orally medicated conceptions were similar to spontaneous conceptions on all thyroid related variables, and therefore the two groups were combined for analysis. Although there was a nonsignificant difference in thyrotropin (TSH) levels postconception (3.8 mIU/L vs. 2.2 mIU/L, p = 0.30), there was no difference in TSH levels after increase in thyroid replacement dose (1.7 mIU/L vs. 1.1 mIU/L, p = 0.30) between patients who conceived after gonadotropin stimulation compared with those who conceived spontaneously or with oral medications. The mean percent dose increases for the nongonadotropin and gonadotropin pregnancy groups were 30.6% and 32.4%, respectively.

Hypothyroid patients who conceive after gonadotropin stimulation or with oral medications for ovulation induction do not need additional thyroid supplementation compared with those who conceive spontaneously.