There are two broad categories of thyroid disease.
These are hyperthyroidism, where more thyroid hormone is produced than the body requires, and hypothyroidism, where less thyroid hormone is produced. Both conditions 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 these 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 chapter.
Some forms of hyperthyroidism may affect the newborn and the details on this are found in this chapter. 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 chapter.
Treatment of hypothyroidism in the pre-conception and pregnancy period is by simple replacement of the hormone. It is safe, inexpensive and very effective.
Thyroid disease and fertility
Can thyroid disease interfere with fertility?
Yes. A woman suffering from hypothyroidism, the so-called ‘under-active thyroid’ may have difficulty conceiving.
Some women with hypothyroidism contact their doctor about infertility and the condition is discovered in the process of investigating the cause of sub-fertility.
Hypothyroidism (Underactive thyroid) and fertility
Why would low thyroid hormone cause infertility?
It causes failure to ovulate. This may be through an interference with the normal hormonal environment in the body.