For patients with underactive thyroid (hypothyroidism) who are pregnant
or hoping to become pregnant 

There is now substantial evidence that thyroid deficiency during pregnancy can result in some problems in development  in children. In the early part of pregnancy the developing foetus is entirely dependent on the mother's thyroid hormone, so it is vitally important that the pregnant woman's thyroid  hormone levels are adequate.

Hypothyroid women on T4 treatment should have their TSH level checked when pregnant and will need to increase their dose of T4 by a small amount (25 or 50 mcg/day).

Sadly these facts are not yet widely known, and a recent study in a large District Hospital showed that TSH was not being checked when it should be.
Because of this the British Thyroid Association issued an interim statement in November 2001:

 ''Good practice recommends that pregnant women who are at risk of thyroid disorders should have thyroid tests checked at antenatal booking. These groups include women known to have or have had thyroid disease, also patients with type I diabetes, any woman with a family history of thyroid disease and any woman with symptoms suggestive of thyroid disease.''

For women about to become pregnant, we recommend to check the TSH levels before conceiving and adjust the dose of T4 if necessary. The dose will still need to be increased in the first few weeks of pregnancy.

The British Thyroid Association intends to address this further and to promote general awareness of this very important matter.