థైరాయిడ్ పరీక్ష (TSH / T4)

Why are the TSH normal ranges in pregnancy different from the standard lab ranges?

In pregnancy, hCG (the pregnancy hormone) cross-reacts with the TSH receptor and mildly stimulates the thyroid, naturally lowering TSH — especially in the first trimester. This is why the lower end of normal TSH in pregnancy is slightly different. More importantly, the upper end is set tighter (2.5 mIU/L in T1 vs 4.5 in non-pregnant) because the fetus depends entirely on maternal thyroid hormone for brain development in the first trimester. Even a mildly elevated TSH at this stage can affect fetal IQ, so treatment thresholds are more conservative.

I am already on levothyroxine before pregnancy. What do I need to change?

Thyroid hormone requirements increase by approximately 30–50% in pregnancy because the baby requires maternal thyroid hormone in addition to your own needs. Most women on levothyroxine need a dose increase as soon as pregnancy is confirmed — typically increasing by 25–50 mcg/day or taking two extra doses per week. TSH should be checked every 4–6 weeks in the first trimester, and then every trimester thereafter, with dose adjustments as needed. After delivery, the pre-pregnancy dose is usually resumed.

Is levothyroxine safe to take during pregnancy?

Yes, completely. Levothyroxine is identical to the T4 your own thyroid produces. It crosses the placenta minimally (the baby produces its own once its thyroid is active at 12 weeks) and has no harmful effects. Untreated hypothyroidism is far more dangerous than treating it with levothyroxine. Do not stop medication without doctor's advice.

My TSH was slightly high at booking but my FT4 is normal. Do I need medication?

This is called subclinical hypothyroidism (elevated TSH with normal FT4). In the first trimester, many endocrinologists and obstetricians recommend treatment even at TSH 2.5–4.0 mIU/L because of the fetal brain development window. After the first trimester, the threshold may be slightly more relaxed. Your doctor will decide based on your TSH level, trimester, symptoms, and whether you have thyroid antibodies (anti-TPO antibodies), which indicate autoimmune thyroid disease.

How often will my thyroid be checked during pregnancy?

If hypothyroidism is newly diagnosed or already being treated: every 4–6 weeks in the first trimester, then once each in the second and third trimesters (or more frequently if dose adjustments are needed). If thyroid function was normal at booking with no antibodies: no routine repeat is usually needed unless symptoms develop. TSH is re-checked at 6 weeks postpartum as thyroid disease can flare after delivery (postpartum thyroiditis).