From the Research
Target Range for Thyroid-Stimulating Hormone (TSH) Levels During Pregnancy
The target range for TSH levels during pregnancy is a topic of ongoing debate and research. According to various studies, the recommended target range for TSH levels during pregnancy is:
- 0.1-2.5 mU/L for the first trimester 1, 2
- 0.2-3.0 mU/L for the second trimester 2
- 0.3-3.0 mU/L for the third trimester 3
Trimester-Specific Reference Intervals
It is essential to note that trimester-specific reference intervals for TSH levels may vary depending on the population and assay used. Some studies suggest that institutions should calculate their own pregnancy-specific reference intervals rather than relying on fixed universal cutoff concentrations 2.
Controversy Surrounding TSH Cutoffs
There is ongoing controversy surrounding the optimal TSH cutoffs for pregnancy, with some guidelines recommending stricter cutoffs and others suggesting higher cutoffs 3. The American Thyroid Association (ATA) revised its guidelines in 2017, recommending an upper cutoff limit of 4.0 mIU/L when local population-specific reference ranges are not available 3.
Studies on TSH Levels and Pregnancy Outcomes
Several studies have investigated the relationship between TSH levels and pregnancy outcomes, including:
- A study of 78 women with hypothyroidism, which found that TSH levels above 2.5 mU/L were not associated with adverse fetal and maternal outcomes 1
- A study of 1858 pregnant women, which found that mildly elevated TSH levels between 2.5 and 4.0 mIU/L were not associated with adverse pregnancy outcomes 4
- A study of 4643 women, which found that women with TSH levels above 5 mU/L were more likely to deliver infants of lower birth weight, but there were no other differences in obstetric outcomes between groups 5