From the Research
Target TSH Levels in Pregnancy
The target levels for Thyroid-Stimulating Hormone (TSH) in the third trimester of pregnancy are:
- ≤3 mIU/L, as recommended by recent guidelines 1
- Greater than 2·5 mIU/L in the first trimester and greater than 3 mIU/L in the second and third trimesters, as defined by some authors 2
Key Findings
- A study found that 46% of levothyroxine-treated women had a TSH level greater than 2.5 mU/L, with 7.4% greater than 10 mU/L 3
- Women with TSH greater than 2.5 mU/L in the first trimester had an increased risk of miscarriage compared with women with TSH 0.2-2.5 mU/L 3
- The majority of women with hypothyroidism do not achieve the recommended preconception and early gestation TSH targets 4
TSH Levels and Pregnancy Outcomes
- TSH levels above 2.5 mU/L were not associated with adverse fetal and maternal outcomes in one study 4
- However, another study found that women with TSH greater than 2.5 mU/L in the first trimester had an increased risk of miscarriage 3
- The risk of miscarriage was increased in women with TSH 4.51-10 mU/L and TSH greater than 10 mU/L, but not with TSH 2.51-4.5 mU/L 3