In conjunction with World Thyroid Day (May 25), we take a look at thyroid problems that may occur during pregnancy, and how this affects the developing foetus.

THYROID diseases may be broadly divided into two categories:

Hormonal problems, which may be due to an excess of thyroid hormone production (hyperthyroidism) or the opposite, which is insufficient thyroid hormone production (hypothyroidism).

An enlarged thyroid gland (goitre) or nodules in the gland, which may be cancerous or non-cancerous.

Generally, only hormonal problems affect pregnancy. Optimal levels of thyroid hormone are essential to health from foetal life to adulthood. This review will therefore concentrate only on hyperthyroidism and hypothyroidism.

Problems with conception

Both hyperthyroidism and hypothyroidism affect the levels of female hormones, leading to menstrual problems and infertility. In addition, women with hypothyroidism may have raised prolactin levels (the hormone which promotes breast milk production, so high levels simulate breastfeeding), further diminishing fertility.

Diagnosing hypothyroidism in pregnancy is a problem because it is usually silent. The women at risk would be those with a family history of thyroid disease. However since anyone can develop hypothyroidism, and since it may be harmful to the pregnancy and foetus, all pregnant women and those intending to be pregnant should ideally be screened.

However, this is not universally accepted. In the US, this is the norm, but not in the UK. Other countries go a step further and screen all women over a certain age whether or not they intend to have a child.

The reason for this controversy is because studies have not proven conclusively that population wide screening at the expense of the government will lead to an improvement in pregnancy and foetal outcomes. But if cost is not a problem, I would suggest that pregnant women or those contemplating pregnancy request for a simple blood test to screen for hypothyroidism.

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Thyroid disease