At what values (T3, T4, TSH) does it become dangerous for my baby?
An underfunction of the thyroid gland is diagnosed on the basis of an altered hormone level in the blood. The control hormone TSH is produced in the brain and leads to the release of T3 (triiodothyronine) and T4 (thyroxine) from the thyroid gland into the maternal bloodstream. From there the thyroid hormones are transported via the placenta to the baby, where they contribute to the regulation of fetal development.
A distinction is made between latent and manifest hypothyroidism. In latent hypothyroidism, the concentrations of the free hormones T3 and T4 are still within the normal range, only the TSH value is elevated. The body initially tries to compensate for the hypothyroidism by increasing the production of TSH by the pituitary gland, which leads to the release of T3 and T4.
As the disease progresses, the body is no longer able to compensate for the hypothyroidism and hypothyroidism becomes manifest. TSH levels continue to rise, but the concentration of free T3 and T4 in the serum is also reduced. Due to the decreasing level of thyroid hormones the fetus is threatened with developmental damage and the risk of premature birth increases.
The reference ranges in which the concentration of thyroid hormones in pregnant women should lie depend on the trimenon and cannot be determined with certainty. The following values can be used for orientation: If the concentration of TSH rises above these values, the free T3 and T4 should also be determined in any case. A clarification and exact interpretation of the blood values should always be carried out by the gynecologist. Hormone substitution is used in both latent and manifest hypothyroidism.
- In the 1st trimester (third of pregnancy) the TSH value should be between 0.1 and 2.5 mU/l,
- In the 2nd trimester at 0.2 – 3 mU/l
- In the 3rd trimenon at 0.3 – 3mU/l.
