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Thyroid UK
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Pregnant and under active thyroid

Hi - i am 16 weeks pregnant, and i was just told that I have an under active thyroid. I am worried about the affects on the baby. I wasn't told if the risk was high or low , however she did tell me that the effect of low thyroid affects IQ and brain development . 

I am now on medication, what the the chances that my baby will be affected? Can I still have a normal baby or do I have to prepare my self for something different 

Any Advice would be appreciated


4 Replies

Welcome to the forum, J_Molondon.

The foetus will have developed it's own thyroid gland by 12 weeks and will no longer be dependent on maternal thyroid hormone.  Your own thyroid hormone has probably been depleted by the demands of the foetus.  If the baby is developing normally you should expect to have a healthy baby.  Newborns are given a heel prick blood test to check thyroid levels before discharge from hospital.


I am not a medical professional and this information is not intended to be a substitute for medical guidance from your own doctor. Please check with your personal physician before applying any of these suggestions.


thank you . I am also confused with the results . The THT is 3.33 and free T4 is 13.0 . this confuses me as to why they think i have an under active Thyroid 

i will take the medicine prescribe and gives me relief that probably its more precautionary than anything else  



The range is lower for women planning conception and pregnant.  NICE recommend TSH should be in the low-normal range 0.4-2.0 with FT4 in the upper range.


Taking the medication will reduce the chances of miscarriage and post-partum thyroiditis.

It's possible that your pregnancy has caused the hypothyroidism and you may become euthyroid a few months after delivery.


thank you very much !


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