Thyroid Disease in Pregnancy: Symptoms, Testing and Treatment Approach

Thyroid diseases in pregnancy are conditions in which the thyroid gland in the neck works less or more than it should during or before pregnancy, and they are usually detected with a blood test and managed under a doctor's follow-up. Because thyroid hormone is also important for the baby's development, it matters that the problem is treated or the medicine is adjusted correctly. Do not stop or change your medicine without asking your doctor.

What does the thyroid do in pregnancy?

The thyroid is a gland at the front of the neck that makes a hormone regulating metabolism. The production of this hormone is controlled by a stimulating hormone released from the pituitary gland. In pregnancy, thyroid hormone production naturally increases; low iodine intake and autoimmune (the immune system turning against the body's own tissue) conditions are among the reasons for this change.

How are the symptoms and treatment assessed if your thyroid is underactive?

When the thyroid gland works less than it should, symptoms such as tiredness, feeling cold, dry skin and hair, and constipation can be seen; the diagnosis is made with a blood test. In some cases the stimulating hormone from the pituitary can come out high even though the thyroid hormone level is within normal limits; this picture is assessed according to the person. It is known that a well-treated underactive thyroid does not harm the mother or baby; if untreated, it can be linked with miscarriage, preterm birth, low birth weight and the baby's brain development. The treatment is a thyroid hormone tablet regarded as safe in pregnancy; in most people a higher dose is needed in pregnancy, but your doctor adjusts the dose according to blood test results. Do not stop the medicine or change its dose on your own; both too little and too much treatment can be harmful.

What is done if your thyroid is overactive?

The most common cause of an overactive thyroid is an autoimmune condition called Graves' disease. Symptoms may include weight loss, palpitations or a fast heartbeat, intolerance of heat, trembling, mood changes, enlargement of the thyroid gland and prominence of the eyes. In cases that are not well controlled, the likelihood of conditions such as pre-eclampsia, preterm birth and low birth weight may increase; it is also important for the baby's development. In treatment, a group of medicines used at the lowest effective level (antithyroid medicines) is generally preferred; the doctor decides which medicine to use and when. If a pregnancy is unexpectedly noticed while you are taking antithyroid medicine, it is important to tell the team following you without delay.

How does a temporary overactivity due to pregnancy progress?

In the first half of pregnancy, a temporary picture of overactivity due to the pregnancy hormone can be seen in some people. This usually settles by itself, and medicine treatment is rarely needed.

Do symptoms alone show thyroid disease?

Symptoms of an underactive thyroid include tiredness, feeling cold, dry skin and hair, and constipation; symptoms of an overactive thyroid include weight loss, palpitations, intolerance of heat, trembling and mood changes. Palpitations, trembling or tiredness can also be seen in pregnancy for other reasons; for this reason a symptom alone does not give a diagnosis, and the diagnosis is confirmed with a blood test. When you notice these complaints, tell your doctor at your check-up.

Who has a thyroid test?

A thyroid test can be offered in early pregnancy to those who have had a thyroid problem or thyroid surgery in the past, those who have swelling in the thyroid gland, those with another autoimmune disease, and those who had a stillbirth or late miscarriage in a previous pregnancy. Routine thyroid testing of all pregnant women is not a common recommendation; the test is requested in situations that carry risk. Practice on this varies according to country and institution; the doctor following you will explain when and why the test is requested for you.

How are your medicines and blood test check-ups planned?

In people who are being treated, the dose of the medicine may need to be adjusted again in pregnancy; for this reason it is important to share your pregnancy with the doctor who prescribes your medicine. Regular blood tests form the basis of monitoring; in some cases an extra ultrasound may be requested to assess the baby's growth. Your need for iodine increases in pregnancy; because an excess of multivitamin supplements can be harmful, review the supplements you use, including those containing iodine, with your doctor. Do not add supplements or change the medicine dose on your own.

What does it mean for the mother and baby?

Good control of thyroid disease reduces the likelihood of possible problems for the mother and baby; for this reason keeping to monitoring and treatment is important. In cases that stay uncontrolled, the likelihood of some problems that are also important for the baby's development may increase. This is a likelihood and does not mean a definite outcome; your doctor assesses what your situation means for you.

How are birth and postnatal follow-up planned?

Well-controlled thyroid disease generally does not change the timing or mode of birth; in some situations with Graves' disease, a high antibody level or a history of antithyroid medicine, closer monitoring of the baby's heartbeat during birth may be planned. After birth the medicine dose generally returns to the level before pregnancy or can be stopped, and the thyroid test is repeated; babies at risk may have a thyroid test after birth. Medicines for both an underactive and an overactive thyroid are regarded as safe during breastfeeding.

In the first year after birth, a temporary thyroid inflammation of autoimmune origin (postnatal thyroiditis) can develop in some people. This mostly heals by itself; in some people it can later turn into an underactive thyroid. If you are having marked postnatal mood changes, a thyroid test can also be part of the assessment.

How can you support yourself?

• Use your medicine as your doctor recommends; do not stop it or change its dose on your own.
• Do not miss your blood test check-ups.
• If you are planning a pregnancy, talk beforehand with the doctor who prescribes your thyroid medicine.
• Review the supplements you use, including those containing iodine, with your doctor.
• If you notice a new swelling in your neck, report it at your check-up.
• If you feel anxious, share this with your health team.

What can you ask your doctor about your thyroid condition?

• Ask why my thyroid test was requested and what the result means.
• If you take medicine, find out how the dose will be adjusted in pregnancy.
• Ask how often the blood test check-ups will be done.
• Talk about whether the birth plan will change according to the thyroid condition.
• Ask which tests will be done after birth and about medicine use while breastfeeding.