Changes in TSH levels after pregnancy in women undergoing fertility treatment taking thyroid hormones

Abstract

When women who are taking thyroid hormones become pregnant, they are often requested to take double doses twice a week. However, it remains unclear whether this treatment also applies to women with subclinical hypothyroidism (TSH >4.0 mU/L) or high normal TSH (TSH 2.5–4.0 mU/L). Therefore, the present study compared TSH levels before and after pregnancy (4–10 weeks gestation, mean 6.7 weeks) in 89 women undergoing fertility treatment who were taking levothyroxine (LT4). TSH levels before pregnancy ranged between 0.5 and 2.5 mU/L and the LT4 dose was not changed at the time of pregnancy. TSH levels decreased after pregnancy in 49 women and increased in 40 women. No significant differences were observed in TSH levels between before and early pregnancy (1.48 ± 0.54 and 1.67 ± 1.59 mU/L, respectively, p = 0.263). In conclusion, when women with subclinical hypothyroidism or high normal TSH who are taking LT4 for fertility treatment become pregnant, it is preferable to adjust the dosage based on TSH levels in early pregnancy rather than immediately increasing the dosage without testing.