Hyperthyroidism - Treatment in Pregnancy
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Doctors prefer to use propylthiouracil (PTU) during pregnancy, because it is considered a
safer option than carbimazole. Carbimazole can cause a rare congenital abnormality of the
scalp, called aplasia cutis. PTU however can cross the placenta and may cause
hypothyroidism in the baby. Usually the lowest possible dose is given to avoid complications
in the baby.

If you take PTU when you are pregnant then you must monitor your thyroid hormone levels
every month. Thyroxine levels need to remain optimal (upper third of the normal reference
range), because studies consistently confirm that low maternal free circulating thyroxine (not
the maternal TSH), also referred to as hypothyroxinemia, can cause developmental delay or
future neurodevelopmental difficulties in the baby.

PTU can control the symptoms within a few weeks. Both PTU and carbimazole can be
excreted in the breast milk and it may not be safe for the baby. The evidence so far is
inconclusive. PTU is considered safer during breastfeeding than carbimazole, because
smaller amounts are excreted in the breast milk.

If hyperthyroidism cannot be controlled with low dose antithyroid medication, then surgery
may be recommended. It is possible to have a thyroidectomy (removal of the thyroid gland)
whilst pregnant. The safest time to do the surgery is in the second trimester. Antithyroid
drugs are given prior to the surgery to avoid ‘thyroid storm’.

Radioactive iodine should never be used in pregnancy, because it can cross the placenta
and destroy the baby’s thyroid gland.


Disclaimer  The information provided is for educational purposes only and is not intended to be medical
advice. The contents must not be relied upon in place of advice and treatment from a qualified medical
practitioner. Thyroid WA Support Group Inc. and the author disclaim any liability whatsoever. Copyright ©
Monique Atkinson 2011

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