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What Causes Low TSH Levels Despite Taking Synthroid?
Question: Im looking for an endocrinologist to answer my question. Prior to getting pregnant i have had hypothyroidism for 15 years. I was on 125 mcg of synthroid with a tsh of .31. Im now 12 weeks and my endo upped my dose to 175 mcg. My last labs showed a tsh of .06 and t4 of 16.1 but a normal t3 of 132. Im really worried hes suppressed my tsh so much. I had a miscarriage last year because my ocerall levevls were too low with a tsh of 6.9. Im afraid though he has me too far in the other dorection. Id love a second opinion!
Brief Answer:
Thyroid
Detailed Answer:
I follow what you ate saying. The TSH can be suppressed in the first 3 months if you had significant vomiting due to a severe version of morning sickness called 'Hyperemesis Gravidarum'. If you had this then the TSH is low most likely due to that. It does not require any treatment and it typically normalizes on it's own. Your total T 4 legend will also normally be elevated above the normal range for non pregnant adults so do not worry as this is also normal for pregnancy. I would now like to know the reference range for normal on your XXXXXXX report for T3 and T 4
Thyroid
Detailed Answer:
I follow what you ate saying. The TSH can be suppressed in the first 3 months if you had significant vomiting due to a severe version of morning sickness called 'Hyperemesis Gravidarum'. If you had this then the TSH is low most likely due to that. It does not require any treatment and it typically normalizes on it's own. Your total T 4 legend will also normally be elevated above the normal range for non pregnant adults so do not worry as this is also normal for pregnancy. I would now like to know the reference range for normal on your XXXXXXX report for T3 and T 4
Above answer was peer-reviewed by :
Dr. Chakravarthy Mazumdar
I didnt have hyp grav. I had minimal morning sickness which is why is worries me. My t3 from before i was pregnant was 83 and t4 8.5. So you dont think im on too much of my tsh is suppressed that low?
Brief Answer:
Low TSH
Detailed Answer:
Kindly note the following:
1 Your TSH of 0.31 before pregnancy was also slightly lower than normal to begin with.
2 The TSH test result itself can vary by unto 20% when checked on the same blood sample, again in the same laboratory as well as another laboratory. Which means that it is possible that if your TSH of 0.31 were rechecked in the same laboratory or another on the same sample, or a fresh blood sample almost around the same time, there is a good chance it would read somewhere between 0.25 to 0.37
The point I am making is that we tend to go by trends and patterns in thyroid lab results, as is the case in many situations within endocrinology.
It is a complex science.
3 That being said, if the TSH is significantly suppressed or elevated, one can surmise an abnormality.
4 Given your circumstance, it was still likely prudent to have increased your synthroid dose when pregnancy occurred because requirements during pregnancy increase by 33 to 50%
5 During pregnancy, the total T3 and T4 can rise upto 1.5 times the upper limit for normal for non-pregnant adults.
So your Total T4 is likely still normal.
6 Another thyroid fact is that various labs may use different methods for running T3 and T4 tests. So the range for normal and pregnancy can vary. That is why it is important to know your lab's normal range for T3, T4 and TSH
However, many labs do not provide the normal range for pregnancy. But it is still possible to interpret the results from whatever reference range is provided.
7 Even if the current lab reports tend to suggest a slightly higher dose, it has not been shown to be harmful as it appears to be a mild suppression only.
Even if you were not formally diagnosed with Hyperemesis, hCG (human chorionic gonadotropin) produced by the placenta can have this effect on thyroid labs, especially in the first 3 months after which its effects tend to wane.
This does not require any treatment as long as the thyroid labs are not significantly abnormal.
8 Sorry to note your miscarriage last year. A high TSH has been associated with the risk of such problems. So it is good that your TSH before getting pregnant this time was not abnormally high.
The typical TSH target during pregnancy is
0.1 to 2.5 in first trimester
0.2 to 3 in second trimester
0.3 to 3 (or 3.5) in third trimester
Low TSH
Detailed Answer:
Kindly note the following:
1 Your TSH of 0.31 before pregnancy was also slightly lower than normal to begin with.
2 The TSH test result itself can vary by unto 20% when checked on the same blood sample, again in the same laboratory as well as another laboratory. Which means that it is possible that if your TSH of 0.31 were rechecked in the same laboratory or another on the same sample, or a fresh blood sample almost around the same time, there is a good chance it would read somewhere between 0.25 to 0.37
The point I am making is that we tend to go by trends and patterns in thyroid lab results, as is the case in many situations within endocrinology.
It is a complex science.
3 That being said, if the TSH is significantly suppressed or elevated, one can surmise an abnormality.
4 Given your circumstance, it was still likely prudent to have increased your synthroid dose when pregnancy occurred because requirements during pregnancy increase by 33 to 50%
5 During pregnancy, the total T3 and T4 can rise upto 1.5 times the upper limit for normal for non-pregnant adults.
So your Total T4 is likely still normal.
6 Another thyroid fact is that various labs may use different methods for running T3 and T4 tests. So the range for normal and pregnancy can vary. That is why it is important to know your lab's normal range for T3, T4 and TSH
However, many labs do not provide the normal range for pregnancy. But it is still possible to interpret the results from whatever reference range is provided.
7 Even if the current lab reports tend to suggest a slightly higher dose, it has not been shown to be harmful as it appears to be a mild suppression only.
Even if you were not formally diagnosed with Hyperemesis, hCG (human chorionic gonadotropin) produced by the placenta can have this effect on thyroid labs, especially in the first 3 months after which its effects tend to wane.
This does not require any treatment as long as the thyroid labs are not significantly abnormal.
8 Sorry to note your miscarriage last year. A high TSH has been associated with the risk of such problems. So it is good that your TSH before getting pregnant this time was not abnormally high.
The typical TSH target during pregnancy is
0.1 to 2.5 in first trimester
0.2 to 3 in second trimester
0.3 to 3 (or 3.5) in third trimester
Note: For more information on hormonal imbalance symptoms or unmanaged diabetes with other comorbid conditions, get back to us & Consult with an Endocrinologist. Click here to book an appointment.
Above answer was peer-reviewed by :
Dr. Chakravarthy Mazumdar
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