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What do reduced FT4 and TSH levels at 22 weeks pregnancy indicate?

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Posted on Fri, 18 Dec 2020
Question: Hello Doctor,

My wife is 22 weeks pregnant as of now. We recently had a Thyroid Function Test done and our doctor had shown concerns about her reduced FT4 and TSH levels since last test in November. We have attached all the reports here. Could you help us understand the lab results and what interpretations we should take from these.

We would really appreciate any guidance that you can provide on this.
doctor
Answered by Dr. Minal Mohit (59 minutes later)
Brief Answer:

Is she on treatment presently for thyroid dysfunction?

Detailed Answer:

Hello,

Sure I will explain all. I have gone through all your reports, I could see a lower side FT4 and also a normal TSH in all reports with a negative TPO antibody report.

But please tell me
1. Is she on treatment presently
2. Any family history of thyroid disease
3. Is this first pregnancy ? Any abortions?

Hope I have answered your query. Let me know if I can assist you further.
Above answer was peer-reviewed by : Dr. Yogesh D
doctor
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Follow up: Dr. Minal Mohit (43 minutes later)
Hello Doctor. Thanks for the response. Below are the responses to your query -

1. She is not on any thyroid medication. All she is taking is iron and calcium supplements (general pregnancy supplements).

2. Her mother than Hypo Thyroid problem long ago but is no longer prevalent as of now (for last may years).

3. Yes this is her first pregnancy - no abortions or any complications earlier.

Kindly advise.
doctor
Answered by Dr. Minal Mohit (18 minutes later)
Brief Answer:

All reports seem to be in normal range.

Detailed Answer:

Hello,

Let me explain one by one and try to relieve your stress. First and foremost, believe me, there is nothing to worry.

1. TSH is usually low in pregnancy. HCG is another hormone , formed by placenta. HCG and TSH match structurally so once HCG start rising as pregnancy progresses, TSH is suppressed.

So low TSH is not something to worry unless it is coupled by very high FT4 and unless it is in 0.0xy decimals.

2. FT4 is usually around 1.4 ng /dl but that is for a patient on thyroxine treatment. FT4 in low normal range for a lady not on treatment, is not a concern to treat.

3. Anti TPO , if high , is a marker of autoimmunity , and may be considered a marker to treat. but in your wife's case, it is normal or negative.

4. mother has some vague history with no documentation as of now, may not be important again.

5. spontaneous pregnancy, with continuation up to 22 weeks is a sign of normal thyroid function again

5. cortisol is also normal, which suggests normal pituitary function.

So the crux is, no concern as of now about thyroid. do repeat a test in 6 weeks time and let me know regards!

note: I am answering your query from my busy OPD, so excuse me for spelling and grammatical errors.

Hope I have answered your query. Let me know if I can assist you further.
Above answer was peer-reviewed by : Dr. Yogesh D
doctor
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Follow up: Dr. Minal Mohit (20 minutes later)
Thank you doctor. We were really concerned - as our doctor said that simultaneous decline of both FT4 and TSH could be a sign of some sort of pituitary tumor. We are really thankful for your response.
doctor
Answered by Dr. Minal Mohit (13 hours later)
Brief Answer:

True in a normal scenario.

Detailed Answer:

Hello,

Your doctor is very right in any normal scenario. In pregnancy the fluctuations are different. also a normal cortisol with continuing pregnancy , rules out pituitary involvement.

Still, we recommend a repeat check at every 6 weeks i.e 28th week and 34th week. If your doctor decides to add thyroxine, even that can be considered.

Hope I have answered your query.

Take care

Regards,
Dr Minal Mohit, Endocrinologist

Above answer was peer-reviewed by : Dr. Nagamani Ng
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Dr. Minal Mohit

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Practicing since :1998

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What do reduced FT4 and TSH levels at 22 weeks pregnancy indicate?

Brief Answer: Is she on treatment presently for thyroid dysfunction? Detailed Answer: Hello, Sure I will explain all. I have gone through all your reports, I could see a lower side FT4 and also a normal TSH in all reports with a negative TPO antibody report. But please tell me 1. Is she on treatment presently 2. Any family history of thyroid disease 3. Is this first pregnancy ? Any abortions? Hope I have answered your query. Let me know if I can assist you further.