Thyroid disease in pregnancy

There are two broad categories of thyroid disease.

These are hyperthyroidism, where more thyroid hormone is produced than the body requires, and hypothyroidism, where the thyroid hormone produced is insufficient. Both hyperthyroidism and hypothyroidism have a significant impact on the ability to conceive, the successful carrying of pregnancy and on the fetus itself.

Hyperthyroidism is not one simple condition. It may be caused by a variety of diseases, all leading to a common consequence: the production of excess hormone by the thyroid gland. The outward and physiological effects will, therefore, be more or less the same. This condition is relatively common and affects roughly two out of every thousand pregnant women (2/1000).

Most of those affected with hyperthyroidism will have a condition known as Graves' disease, which is explained in this chapter. There are several other less common causes of hyperthyroidism, also explained below.

Ideally, the condition should be recognized before conception. This is not always the case, as the symptoms may be so mild that they do not cause undue concern.

Sometimes, the diagnosis is made during investigations for fertility difficulties, and often the condition is discovered for the first time during pregnancy.

Treatment for hyperthyroidism needs to be maintained during pregnancy to optimize the successful outcome of the pregnancy. Some forms of medication are completely safe in pregnancy, while others are not. All this is clearly discussed in this section.

Some forms of hyperthyroidism may affect the newborn and the details on this are found in this section. However, these effects are usually transient and relatively easy to treat.

Hypothyroidism or deficiency of the thyroid hormone is also important with regard to fertility and successful pregnancy.

Investigations for infertility or reduced fertility will, in most instances, include thyroid function tests, as there is firm evidence that hypothyroidism can make conception difficult. Moreover, untreated hypothyroidism sometimes causes various minor and occasionally serious problems in pregnancy. We have explained all these in this section.

Treatment of hypothyroidism in the pre-conception and pregnancy period is by simple replacement of the hormone. It is safe, inexpensive and very effective.

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The idea that thyroid disease is always easily identifiable, such as with goitre (above), is a myth. Thyroid disease can be discovered for the first time during pregnancy