Thyroid gland and pregnancy

Information sheet for women of childbearing age after radioiodine therapy

Due to a thyroid tumor, you have undergone surgical removal of the thyroid gland and radioiodine therapy. We would like to give you the following information for a possible future pregnancy:

In principle, there are no concerns about pregnancy following radioiodine therapy, as no relevant genetic damage is known. However, as a general precaution, we recommend avoiding pregnancy for at least 6 months after radioiodine therapy.

As your thyroid gland has been removed, without hormone replacement with L-thyroxine or Euthyrox, this would result in an underactive thyroid (hypothyroidism). After radioiodine therapy, you are therefore dependent on hormone replacement. We will adjust your hormone status depending on the stage of your tumor. If the primary tumor stage is low, a basal TSH setting in the low normal range between 0.3 and 1.0 IU/ml is sufficient; for higher-grade tumors, the TSH should be completely suppressed (TSH < 0.1µU/ml).

However, these guide values change during and before a planned pregnancy.

If you want to become pregnant, please note the following:

Fertility may be limited in women with existing hypothyroidism. Hyperthyroidism can also complicate conception. Before pregnancy (pre-conception), the TSH value should be < 2.5 lU/ml. As a low TSH value is recommended due to your thyroid tumor, it may be necessary to reduce the dose of L-thyroxine or Euthyrox. This should be done in consultation with us or your gynecologist.

If you are already pregnant, please note the following:

The correct thyroid metabolism has a lasting effect on the maturation of the unborn child, particularly on the development of the brain, especially in the first half of pregnancy. As the fetal thyroid gland only starts to function at the end of the third month of pregnancy, it is essential that the pregnant woman has an adequate supply of thyroid hormone, as the thyroid hormones reach the child via the placenta. If the correct dose of medication is administered, the normal development of the child is ensured.

We therefore recommend the following to regulate your thyroid function, regardless of the stage of your tumor:

The drug of choice before and during pregnancy is L-thyroxine.

During pregnancy, the TSH value should be in the trimester-specific (trimester = third trimester of pregnancy) reference range: In the 1st trimester between 0.1-2.5 IU/ml, in the 2nd trimester between 0.2-3.0 IU/ml and in the 3rd trimester: 0.3-3.0 IU/ml

The need for thyroid hormones often changes during pregnancy. It is often necessary to increase the substitution dose by 25-50% in the course of the pregnancy. Even mild hypothyroidism should be avoided by adjusting the hormone dosage in good time.

We recommend checking the TSH value and the free thyroid hormone values fT4 / fT3 before a planned pregnancy and adjusting them optimally. Monthly checks are necessary during pregnancy. 6 weeks after the birth, the TSH value and the tumor marker TG should be checked again. After pregnancy, the TSH value is again based on the reference value depending on the tumor stage.

If your TSH value has already been adjusted to <2.5 IU/ml (preferably <1.5 IU/ml) before pregnancy and a rapid determination of the TSH value for individual dose adjustment is not possible when the pregnancy becomes known (positive pregnancy test or missed period), the following procedure can also be used: Take an additional daily dose of L-thyroxine or Euthyrox twice a week (9 instead of 7 tablets/week). This will increase the L-thyroxine dose by 25-30%. Given the long half-life of thyroxine, this ensures the necessary increase in dose that is often required during pregnancy. In this case, however, please make an appointment with your family doctor/gynaecologist immediately for a laboratory test.

During pregnancy and breastfeeding, we strongly recommend taking an additional 150 - 200 µg of iodide per day to ensure that the child has an adequate supply of iodine. Attention should also be paid to folic acid intake.

If you have any questions, please contact our follow-up outpatient clinic on 089 4400 7 4636 or the special outpatient clinic of Prof. Dr. C. Spitzweg in the Medical Clinic II on 4400-73003.

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