As soon as a woman being treated for hypothyroidism falls pregnant, she needs her thyroxine dose increased, says Australian expert, Professor Creswell Eastman.

It is imperative that the developing fetus have sufficient iodine right from conception to ensure they reach their full intellectual potential, said Professor Eastman, Clinical Professor of Medicine at the University of Sydney on a recent Healthed podcast.

Women who are already taking thyroxine prior to conception will need their dose increased by at least 25%, and this may have to be increased even further (sometimes up to 50% higher) but this should be determined by close monitoring especially over the first three months of the pregnancy.

It is important that this increase in dosage is not delayed as the damage done from iodine deficiency in the early stages of pregnancy are not thought to be reversible.

Iodine deficiency in Australia is fairly uncommon, despite it still being the commonest cause of intellectual impairment worldwide, Professor Eastman said.

As most people are aware, Australians used to be protected from this particular deficiency thanks to the dairy industry. The iodophors used as the major cleaning agent in dairy production and storage, meant that milk and milk products were fortuitously ‘contaminated’ with iodine, thereby supplementing the population. As cleaning practices changed, so did our vulnerability to iodine deficiency and the complications associated with this condition.

In the 1990s, Professor Eastman and colleagues showed, courtesy of nationwide research that the prevalence of iodine deficiency was high and morbidity associated with this deficiency – on a population basis – was likely to be significant.

This led to the mandatory inclusion of iodised salt in baked products in Australia, which has largely addressed the issue.

However, the problem associated with the increased demand for iodine in pregnancy remains particularly for women who are known to have thyroid disease.

People who are iodine deficient may present with a goitre. More commonly though a goitre is caused by autoimmune thyroid disease including Hashimoto’s disease. Initial investigations should include an ultrasound, thyroid function tests and thyroid autoantibody tests (especially thyroid peroxidase antibody).

Most people with hypothyroidism however do not have a goitre but present with more subtle, systemic symptoms such as tiredness, weight gain and hair thinning. Their TSH may be only mildly elevated and there may also be a number of comorbidities as well.

It is important to manage expectations early as Professor Eastman says people often attribute all their symptoms to the one condition, and when they don’t all resolve with the standard treatment – monotherapy with thyroxine – they turn to alternative therapies – most commonly dessicated thyroid extract.