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Thyroid in pregnancy
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Pregnancy changes the thyroid's job. That gland in the neck raises its hormone output by about 50%, and the amount of iodine needed each day goes up along with it. It is a factory that suddenly has to produce 50% more.
That makes lab results look different, and it is worth knowing why. In pregnancy, thyroxine-binding globulin, the protein that carries the hormone through the blood, rises. With more carriers there is more hormone being carried, so total T4 and T3 rise, and they peak around week 16.
There is a second effect. hCG, the pregnancy hormone, stimulates the TSH receptor on the thyroid. With that push, TSH in the blood is usually lower than outside of pregnancy.
This adjustment is not a mere lab detail: thyroid hormone is critical to the fetus's neurodevelopment, that is, to how its nervous system forms.
In brief
In pregnancy, thyroid hormone production rises by 50%, and daily iodine requirements go up as well.
A factory that suddenly has to produce 50% more.
Higher thyroxine-binding globulin raises total T4 and T3, which peak around week 16.
hCG stimulates the TSH receptor, so serum TSH is usually lower than outside of pregnancy.
This balance matters because thyroid hormone is critical for fetal neurodevelopment.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingThyroid Disease and Pregnancy, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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