Effect of Thyroid on Pregnancy

Follow up of a case of miscarriage at 11 weeks.

Q: I truly appreciate your prompt response to my query. I forgot to mention that I am under treatment for thyroid, however we planned pregnancy only after it was completely under control. During pregnancy, TSH test was well under normal range. However after the treatment started, my periods, which were otherwise always timely, got delayed by 5 days for the first 2 months. Next month it was on time but heavy and only for 2 days. I conceived post this menstrual cycle. Does such a change in menstrual cycle impact quality of egg?
-By Preeti


It’s unlikely that the pattern of your menses or the quality of your egg caused the abortion. Much more chances are that it was the development of the fetus after conception that might have been affected.

Thyroid dysfunction of any type (hyperthyroidism or hypothyroidism) can be a cause of miscarriage. Since you had some thyroid dysfunction in the past, even though you were adequately treated, this may be the reason for your abortion.

This is because pregnancy influences the functioning of the thyroid tissues. Even in normal pregnancies, a mild hyperthyroidism usually occurs during the first trimester. It disappears itself in later trimesters.

Pregnancy can be a cause in itself for recurrence of Grave’s disease (hyperthyroidism) or Hashimoto’s disease (hypothyroidism) in women prone to thyroid disorders.

Guidelines for Thyroid Hormone Levels 

It is recommended that TSH should be kept below 2.5 mIU/L prior to conception. This lowers the risk of the TSH elevating in the first trimester.

During the first trimester, the TSH level should be maintained at a level between 0.1 and 2.5 mIU/L, 0.2 to 3.0 mIU/L during the second trimester, and 0.3 to 3.0 mIU/L in the third trimester.

If positive for thyroid antibodies, even with normal TSH levels in the early stages of pregnancy, there is a risk of becoming hypothyroid later during term.

How pregnancy affects thyroid functions needs to be clearly understood. Read here for understanding how to manage thyroid dysfunctions during pregnancy.

Take Care

Buddy M.D.

Medical Advice (Q&As) on “Effect of Thyroid on Pregnancy

  1. Preeti

    Dear Dr, I thank you for the clarification.

    I am increasingly getting convinced that the stoppage of fetal growth beyond 6 weeks resulting in miscarriage was not because of egg quality or my age but because of my thyroid problem. I am sharing certain details with you so that it helps me next time when I plan pregnancy.

    On 14th November 2011, I was diagnosed with hypothyroidism with T4 as 15.3 pmoL/L and TSH as 6.47 pmoL/L. I was put on Thyroxine 50mcg (6 days/week) and asked to test AMA and repeat TSH after 4 weeks before planning pregnancy.
    On 30 Dec, 2011, TSH was 3 and AMA as 439. (Unable to locate TSH report but I remember it was under normal range and around 3).

    I was asked to go ahead with the pregnancy plan and repeat TSH after 3 months or on getting pregnant whichever happens earlier.
    I failed to conceive in the months of Jan’12 and Feb’12.
    I repeated TSH on 27th March (as advised to repeat after 3 months) with TSH value coming out 3.6.

    After that I missed my period in April with LMP as 2nd March 2012.
    Since I realized I was pregnant on 8th April, I got TSH tested again and the value was 3.48. Advised medication was Thyroxine 50 mcg on 4 days/week and 2 Tablets (50 mcg) on 3 days/week.

    On 19th April an ultrasound showed a healthy heart beat with 6 weeks pregnancy.
    On 5th May I got monthly TSH test done and TSH was 1.95 which was stated as a very good report, although the fetal growth was already gone by then, and was not realized until 11th week.

    Do you suggest any change in medication going forward?

      1. Preeti

        Dear Doctor,

        Thanks very much for your advice. I truly appreciate your prompt response and the support you have provided despite being anonymous in times I need it badly.

  2. anika

    I have tsh 3.06 in week5 am using 12.5mg and now am 16 weeks can i continue it or i should go for a test again??please let me know am worried..

  3. Satya

    My wife is in 32 weeks pregnent. She had blood test reports show that she is having tsh level 4.10 ulu/ml and t3 1.86 ng/ml and t4 is 14 ug/dl. In her scaning reports cisterna magna 13.2 mm. Kindly give this reports will impact baby health after born

    1. Buddy M.D. Post author

      Nothing serious in the report given. However, your wife has to be careful about controlling her TSH levels within range throughout pregnancy.

      Is she taking any medicines?


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