Are you pregnant and curious about how the thyroid works? Or perhaps you have a known thyroid disease? In order to have normal fertility, i.e. optimize your chances of getting pregnant, the thyroid gland needs to function normally.

About one to two percent of pregnant women have a previously known disorder of thyroid function. The most common is hypothyroidism, which is an underproduction of thyroid hormone. Why is proper thyroid production important during pregnancy? Because normal thyroid function in a pregnant woman is important for the development of the fetal brain and cognitive functions. Before the 12th week of pregnancy, the fetus lacks the ability to produce its own thyroid hormone. During the first half of the pregnancy, the fetus is therefore dependent on normal thyroid hormone levels in the pregnant woman, who supplies the fetus with thyroid hormones during this time. The increased need therefore means that pregnant women need to increase their hormone production. From the 28th week of pregnancy, the fetus is so developed that it can survive on its own hormone production.

What problems can a pregnant woman have when her thyroid gland is not working?

A thyroid disorder can result in too low (hypo) or too high (hyper) thyroid function. Symptoms from the thyroid gland can be diffuse.

If you have low thyroid production (hypothyroidism), you may have symptoms such as:
- Fatigue
- Sluggish stomach
- Coldness
- Sadness
- Pain in muscles and joints
- Low pulse
- Swelling of the face
- Dry skin and hair loss

If you have too much thyroid production (hyperthyroidism), you may have symptoms such as:
- Hyperactivity
- Diarrhoea
- Puffy eyes and visual disturbances
- High heart rate and palpitations
- Trembling, often in the hands
- Abnormal sweating and hot flushes
- Mental and physical fatigue
- Weight loss
- Sleep problems

Hormones are complicated, even for the most knowledgeable. We have three participants in the thyroid dance; TSH, T3 and T4. Hormones are the body's own signaling system and travel in the bloodstream to get to the right place where they can work. In simple terms, thyroid production works like this: Thyroid stimulating hormone (TSH) is produced in the pituitary gland (a gland in the brain) which stimulates the thyroid gland to produce its own hormones. The thyroid gland has two different hormones that it can produce; T3 and T4. This is then passed around in a complicated cycle and the body signals when it needs more or less hormone by sensing hormone levels in the blood. If the body detects too low a level of T3 and/or T4, the pituitary gland starts sending out more TSH. The thyroid gland responds by increasing its production. Similarly, the pituitary gland reduces the production of TSH if we have too high a level of T3 or T4.

What can happen to the thyroid when you become pregnant is that the pregnancy hormone HCG (human chorionic gonadotropin) has a stimulating effect on the thyroid. This is also known as the hormone that tests positive on a pregnancy test. In early pregnancy, this can contribute to an increase in thyroid hormone and therefore a decrease in TSH. TSH can then become 'falsely' low due to the fact that HCG "cheating". This physical change often resolves in the second trimester, and you may need to have new blood tests to see if they correct themselves.

Thyroid hormone production requires iodine, which we get from food. Iodine deficiency is rare in Sweden today, but where do we find iodine in our food? Sources of iodine are mainly animal foods and iodine-enriched salt. Those who currently risk getting too low an intake are therefore vegans and those who do not use iodine-enriched salt. It is common that ready-to-eat food does not contain iodine-enriched salt, so an overly one-sided diet can lead to iodine deficiency.

Thyroid dysfunction can be caused by autoimmune chronic inflammation of the thyroid gland (Hashimoto's disease). In autoimmune disease, the body's own immune system attacks its own body. Hyperthyroidism (toxic goitre) is in most cases caused by Graves' disease. It can also be caused by adenomas (benign glandular tumors) that produce hormones.

Thyroid disease is treated with thyroid-like hormone in tablet form. Not treating an overproduction of thyroid gland increases the risk of premature birth, fetal growth retardation, pre-eclampsia and placental abruption. If you don't treat an underproduction, it may inhibit fetal brain development and may increase the risk of early miscarriage. You can also suffer from thyroid disease after giving birth. If you suspect that you have thyroid disease in the postpartum period, you should seek treatment from your health center.

Thyroid disease is therefore common and it is important to have normal thyroid hormone levels to optimize your chances of getting pregnant, but not least to ensure that you feel good as a pregnant woman and that the fetus develops as it should. If you are very ill with thyroid disease, you may be advised not to become pregnant. When admitted to the maternity ward, pregnant women are usually tested for TSH* to ensure that your thyroid gland is working properly. If you have more severe thyroid disease, you may need to visit a specialist antenatal clinic during your pregnancy. So tell your midwife if you have, or may have, a thyroid condition.

Regional variations exist. In some regions, TSH is taken in all cases; in other regions, TSH is taken only for specific risk factors.

Here you can read about exercise during pregnancy.