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Forum Name: Obstetrics

Question: High TSH and pregnancy


 anuindia - Tue Feb 09, 2010 12:16 am

Hi, I am 29 yrs old female, married for 1.5 yrs. I am on thyroid medication (thyronorm 50), since last 8-9 mnths. My TSH levels keep on fluctuating between 2-6, recent level being 5.58. T3 and T4 are in normal range. Pelvic Sonography report is normal. My physician thinks that it is ok for me to try for conception. But my concern is that if I do conceive, would my child have any mental or visual defects because of my high TSH? What precautions would I need to take? Please guide.
 Dr.M.Aroon kamath - Wed Jun 30, 2010 3:01 am

User avatar Hi,

As you have not mentioned certain important details such as the reason why you are on thyroxin (? thyroidectomy, ? thyroiditis etc), i will provide you with some general information pertaining to your query.

- TRH (thyrotropin releasing hormone) does crosss the placenta.
- Maternal TSH does not cross the placenta.
- Similarly, thyroglobulin does not cross due to its large molecular size.
- as far as T4 is concerned, It appears that when fetal thyroid function is normal, the net flux of maternal T4 to the fetus is very limited. However,in hypothyroid fetuses, placental transfer has been seen to occur + uptake of thyroid hormone from the amniotic fluid through the immature fetal epidermis.
- thyroid antibodies, which are found in autoimmune thyroiditis, can cross the placenta.
- Drugs such as thioamides used in the treatment of maternal hyperthyroidism can cross the placenta and affect the synthesis of fetal thyroid hormones.


Of potentially more concern to the fetus is
the mother with prior treatment for Graves’ disease(for example
radioactive iodine or surgery) who no longer requires antithyroid drugs.In this situation chances of harm to the fetus via placental transfer of thyroid stimulating antibodies may be overlooked.

Overall, the most common cause of hypothyroidism is Hashimoto’s thyroiditis (a form of autoimmune thyroiditis). Approximately, 2.5% of women will have a slightly elevated TSH of >6 and 0.4% will have a TSH >10 during pregnancy.They usually have raised titres of thyroid antibodies which as discussed earlier, can cross the placenta.

Whatever the cause, overt maternal hypothyroidism is not a significant cause of fetal disease because it usually is associated with infertility. If pregnancy does occur, there is a high risk of intrauterine fetal death and gestational hypertension. Most women with milder degrees of hypothyroidism may have no
symptoms.

The effects of maternal hypothyroidism on the fetal and post natal brain development is not very clear and are controversial. Untreated severe hypothyroidism in the mother can lead to impaired brain development in the fetus. However, recent studies have suggested that subtle brain abnormalities may be present in children born to women who exhibited mild untreated hypothyroidism during pregnancy. Several investigators have found effects such as slightly lower performance on IQ tests and difficulties with schoolwork in such children. The most common cause of subclinical hypothyroidism is autoimmune disease (such as Hashimoto's).

Hypothyroid women should have their levothyroxine dose optimized prior to becoming pregnant and should have their thyroid function assessed as soon as pregnancy is detected. Levothyroxine requirements frequently rise during pregnancy, by appproximately 25 to 50%, so the dosage should be tailored to maintain a TSH within the normal range.

Prenatal vitamins containg iron can impair the absorption of levothyroxine.So, ideally, levothyroxine and prenatal vitamins should not be taken at the same time and administrtion should be separated by at least an interval of 2-3 hours.

In case you have an uderlying autoimmune thyroiditis (hashimoto's) causing hypothyroidism and are being treated for the same, then an increasing TSH (after an initial period of stable levels) would indicate that the thyroiditis is continuing to destroy more and more of the thyroid follicles and therefore the TSH is being secreted in increasing amounts to maintain a euthyroid state.

I hope this information may be useful to you.
Best wishes!

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