There are several types of thyroid cancer but the most common is known as 'differentiated' thyroid cancer. Differentiated thyroid cancers can be divided into two sorts, based on the appearance of the tumour cells under the microscope, these are papillary carcinomas and follicular carcinomas. The treatment of the two types of differentiated thyroid cancers is very similar.

Usually the first step in the treatment of differentiated thyroid cancers is surgery. Normally this will involve a total thyroidectomy, removing the tumour and the thyroid gland. Occasionally, for very small tumours, only part of the thyroid gland needs to be removed (a thyroid lobectomy).

Over the years studies have shown that giving high dose radioiodine treatment after surgery does reduce the risk of recurrence of the cancer and increases the chance of cure.

Radioiodine therapy has no long-lasting effect on fertility. Many women have had completely successful pregnancies, with normal healthy children, following radioiodine treatment for thyroid cancer.

There may be very temporary changes in fertility immediately after receiving radioiodine as the treatment does effect hormone levels in the body, but this settles quite quickly. In any case, specialists advise that conception is delayed for at least four months after the treatment in order to allow any temporary effect on the reproductive system to settle completely. This four month delay applies to both men and women after radioiodine treatment.

If someone is found to be already pregnant when radioiodine treatment is being planned it will usually be quite safe to delay the treatment until after the end of the pregnancy (experts suggest radioiodine treatment is still useful provided it is given within one year of the initial surgery to remove the thyroid cancer). If radioiodine therapy is given once a pregnancy is over one thing to be aware of is that breast feeding should be avoided as, for a while, traces of the radioiodine will be present in the mother's milk.

When someone becomes pregnant after radioiodine therapy they will be taking thyroid hormone replacement tablets, usually in the form of thyroxine. It is essential to continue this throughout pregnancy but the doctors will want to do regular blood tests of thyroid function (perhaps every two months) because the dose of thyroxine may need to be adjusted because of the pregnancy.