Are you curious about how thyroid hormones interact with pregnancy, or perhaps you have a pre-existing thyroid condition? In order to have normal fertility, i.e. to optimise your chances of getting pregnant, you need to have normal thyroid function. In this article, we thought we’d dive a little deeper into how the thyroid hormone works.

If you have thyroid disease, you are not alone. About one to two percent of all pregnant people have a previously known disorder of thyroid function. The most common is hypothyroidism, which is the underproduction of thyroid hormone. Why is it important to have a functioning thyroid gland during pregnancy? Because normal thyroid function in pregnant people is, among other things, important for the development of the foetus’s brain and cognitive functions. Before the twelfth week of pregnancy, the foetus lacks the ability to form its own thyroid hormone and therefore it is important that the mother’s production works as it should.

During the first half of pregnancy, the foetus is dependent on normal hormone levels from the pregnant person, who provides the foetus with thyroid hormones during this period. The increased demand therefore means that pregnant people need to increase their hormone production. From the 28th week of pregnancy, the foetus is sufficiently developed to survive on its own hormone production.

Too much or too little thyroid hormone

A thyroid disease can manifest itself in too low (hypo) or too high (hyper) thyroid function. Thyroid symptoms can be diffuse and difficult to detect.

If you have too low a thyroid production (hypothyroidism), you may have symptoms such as:
– Fatigue
– Constipation
– Coldness
– Dejection
– Pain in muscles and joints
– Low heart rate
– Swelling of the face
– Dry skin and hair loss

If you have too high a thyroid production (hypothyroidism), you may have symptoms such as:
– Hyperactivity
– Diarrhoea
– Wide-open eyes and visual issues
– High pulse and palpitations
– Tremors, often in the hands
– Abnormal sweating and hot flashes
– Mental and physical fatigue
– Weight loss
– Sleeping problems

This subject of hormones is complicated, even for the most well-educated on this issue. We have three participants in the thyroid dance: TSH, T3 and T4. Hormones are the body’s own signaling system and travel in the blood to end up in the right place where they can work properly. 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 form; T3 and T4. These then goes around in a complicated cycle and the body itself signals when it needs more or less hormone by sensing the hormone levels in the blood. If the body notices too low a level of T3 and/or T4, the pituitary gland starts to send out more TSH. Then 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 during pregnancy? Well, the pregnancy hormone HCG (human chorionic gonadotropin), you know that hormone that gives us a positive pregnancy test, has a stimulating effect on the thyroid gland in the first trimester and can, in early pregnancy, contribute to an increase in thyroid hormone and thus a decrease in TSH. TSH can then be “falsely” too low due to HCG being “tricked”. This physical change often resolves in the second trimester, and you may need to have new blood tests to make sure they are corrected.

Thyroid hormone production requires iodine, which we get from food. Iodine deficiency is unusual in Sweden today and the most common sources of iodine are primarily animal foods and iodized salt.

Hypothyroidism can be due to autoimmune chronic inflammation of the thyroid gland (Hashimoto’s disease). When afflicted by an autoimmune disease, the body’s own immune system attacks its own body. Hyperthyroidism (toxic goiter) is primarily caused by Graves’ disease. Hyperthyroidism can also be caused by adenomas (benign glandular tumors) that produce hormones.

Thyroid disease is treated with a thyroid-like hormone in tablet form. If you do not treat hyperthyroidism, the risk of giving birth prematurely, of the foetus being stunted, pre-eclampsia and placental abruption increases. If you do not treat hypothyroidism, it risks inhibiting the development of the foetus’s brain and can increase the risk of an early miscarriage.

You can also suffer from thyroid disease after giving birth. If you suspect that you have suffered from thyroid disease in the period after giving birth (postpartum), you can seek care at your health centre.

It is common to have thyroid disease and it is important to have normal hormone levels to optimise your chances of getting pregnant, but not least to ensure that you feel good as a pregnant person and that the foetus develops as it should. When admitted to the maternity ward, pregnant people are usually tested for TSH to make sure their thyroid is working properly. If you have a more severe thyroid disease, you may need to visit a specialist maternity clinic during your pregnancy. So, tell the midwife if you have, or may have, a thyroid disease.

Regional variations do exist. In some regions, TSH tests are done for everyone, in other regions, it is only done if there are specific risk factors.