Thyroid health during pregnancy is very important for both the mother and the unborn child. During pregnancy the mother's thyroid hormone crosses the placenta and is needed for the growth of the fetus. When the mother's thyroid produces either too little or too much of thyroid hormone, serious side effects can occur. So, it is extremely important that during pregnancy the mother's thyroid is working normally.

Pregnancy can be viewed as a thyroid stress test. During pregnancy, the thyroid gland must make 50% more thyroid hormone. To do this, the mother also needs to increase her intake of iodine which is needed by the thyroid gland to make thyroid hormone by 50%. It is recommended that all pregnant and breastfeeding women take a daily prenatal vitamin that contains 150 mcg of iodine.

Hypothyroidism

Having too little thyroid hormone is called hypothyroidism. There are 2 types of hypo-thyroidism: minimal to mild, which is called subclinical hypothyroidism, and severe, which is called overt hypo-thyroidism. Both subclinical and overt hypothyroidism can lead to a miscarriage, preterm delivery and decreased IQ in the unborn child.

Women with hypothyroidism and on thyroid hormone replacement usually need to increase their dose during pregnancy.

This is not surprising as their thyroid gland is unable to produce the extra thyroid hormone required during pregnancy. Before getting pregnant, women on thyroid replacement drug should have their hormone levels checked so their dose can be changed if needed.

In addition to women known to be hypothyroid prior to pregnancy, another 2.5% of all pregnant women are hypothyroid. Most of these women have subclinical hypothyroidism and do not have any symptoms. These women are unable to produce the extra hormone needed during pregnancy because their thyroid has already been partially damaged — usually by the body's immune system attacking the thyroid gland.

Treatment is recommended in women with subclinical hypothyroidism those who have thyroid antibodies. Screening should be done in all women in the following high-risk group for thyroid disease:

* Women with infertility

* Women over 30 years of age

* Women with type 1 diabetes

* Women with a history of miscarriage or pre-term delivery

* Women with family history of thyroid disease, symptoms of thyroid disease or with a large thyroid known as a goitre etc.

Hyperthyroidism

Having excessive amount of thyroid hormone is called hyperthyroidism. It can also be divided into overt and subclinical hyperthyroidism. It is much less common than hypothyroidism and less than 1% of all pregnant women have it.

Overt hyperthyroidism causes miscarriage, gestational hypertension, eclampsia and preterm delivery. Subclinical hyper-thyroidism does not cause any bad outcomes for the mother or unborn child.

The most common cause of hyperthyroidism during pregnancy is Graves' disease, which is also an autoimmune disease. Graves' disease is caused by an antibody in the blood that makes the thyroid gland release too much thyroid hormone. Women with Graves' disease should see their doctor before getting pregnant to ensure that they are on the appropriate dose of anti-thyroid drugs.

Postpartum thyroiditis

Postpartum thyroiditis is a thyroid disease in the postpartum period in women who typically do not have a history of having a thyroid disorder. 8% of all women may develop postpartum thyroiditis. Women with postpartum thyroiditis may be diagnosed any time during the first year following childbirth. If the diagnosis is made in the early stages of the condition, an overactive state is more likely. During later stages of the condition, the thyroid runs out of thyroid hormone and becomes an under-active thyroid. Most women will recover fully and have normal thyroid function at the end of the first year after childbirth.

Thyroid health during pregnancy is important for the mother and developing baby. All pregnant women should take prenatal vitamins with iodine.

Women with pre-existing thyroid disease need special monitoring and treatment during pregnancy. Because both hypo-thyroidism and hyperthyroidism cause serious side effects, first trimester screening of women at high risk for thyroid disease is recommended.

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The writer is an Assistant Professor of Endocrinology Department at Bangabandhu Sheikh Mujib Medical University.