Thyroid and Pregnancy

What is the relationship between thyroid and pregnancy?

The thyroid gland is a gland located at the base of the neck and just in front of the trachea. Its function is primarily to regulate metabolism, and in women it plays a very important role in both reproduction and fertility.

In fact, thyroid dysfunctions are much more common in women than in men, either due to underactivity of the thyroid gland, i.e. hypothyroidism, in which the body produces an insufficient amount of thyroid hormones that slow down the metabolism. However, sometimes the opposite situation occurs, in which the thyroid is overactive and produces an excess of thyroid hormones, a fact that accelerates metabolism. In this case we speak of hyperthyroidism.

Thus, if not detected and treated in time, both hypothyroidism and hyperthyroidism can negatively impact both the health of the pregnant patient and the health of the baby.

As such, thyroid disorders can have a very negative impact on health, increasing the risk of premature delivery and raising the risk of placental abruption, in which the placenta detaches from the inner wall of the uterus before delivery.

Prognosis of the disease

The relationship between the thyroid gland and the pregnant woman can cause various problems.

  • Anti-immune antibodies: 2 to 17% of pregnant women have antibodies against the thyroid, and these women are at increased risk of hypothyroidism during pregnancy.
  • Hypothyroidism: consists of a lack of thyroid hormone and this deficiency mainly affects the central nervous system of the fetus. In particular, it is often associated with a lower IQ of the child.

Iodine deficiency is also very common, although less common in developed countries. It is prevented with iodine supplementation and treated with thyroid hormone.

  • Hyperthyroidism: in this case, hyperthyroidism is the excess of thyroid hormone, and is usually caused by Graves-Basedow disease and transient thyrotoxicosis of pregnancy.
  • Graves-Basedow disease: in cases where it appears before pregnancy, it can cause infertility. In cases of pregnancy, it should be noted that, although rare, the antibodies can pass to the fetus and cause complications. In cases where the disease is uncontrolled, both fetal and maternal complications can occur. It should be noted that in young women when designing a treatment it is necessary to consider pros and cons, especially thinking about possible future pregnancies.

Symptoms of thyroid problems in pregnancy

During pregnancy when suffering from hypothyroidism, there are a number of signs and symptoms that appear with some frequency:

  • Excess fatigue
  • Sensitivity to cold
  • Constipation
  • Dry and flaky skin
  • Thinning hair and hair thinning
  • Muscle pain or weakness
  • Swollen thyroid gland
  • Depression
  • Irritability


  • Weight loss or failure to gain expected weight. Increased appetite, diarrhea or constipation.
  • Fast heart rate with rapid breathing.
  • Heat intolerance
  • Excessive sweating
  • Swollen eyes
  • Painful lump in the neck
  • Muscle weakness and tremors
  • Increased blood pressure
  • Nausea and vomiting

Thyroid crisis should also be mentioned, which occurs when thyroid hormone levels become too high, increasing the body temperature, accelerating the heart rate and causing concentration problems. The affected person may sweat, have vomiting and/or diarrhea. In some cases, seizures occur and the patient may even go into a coma, which is life-threatening if immediate medical assistance is not received.

Close monitoring is essential when thyroid problems are present during pregnancy.

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Medical tests for the relationship between thyroid and pregnancy

When diagnosing a thyroid problem, it is important to know the patient’s health, age, medical history, size of the thyroid gland…

Thyroid function tests check and verify the functioning of the thyroid gland, and include blood tests and imaging tests. Imaging tests include the use of ultrasound, computed tomography and nuclear medicine tests.

What are the causes of thyroid problems during pregnancy?

In general, when talking about maternal hyperthyroidism during pregnancy the most common cause (up to 80% of cases) is Graves’ disease, which occurs in about one in 500 pregnant women.

It can be difficult to diagnose during pregnancy, but is diagnosed with a medical history, physical examination and laboratory tests. Graves’ disease may appear during the first trimester or may worsen during the time a woman has the disorder. It can lead to preterm labor or preeclampsia. There is also a risk of developing a thyroid crisis or thyroid storm.

In cases of hypothyroidism, the most common cause is usually an autoimmune disorder, also known as Hashimoto’s thyroiditis. Hyperthyroidism can occur during pregnancy due to inadequate treatment or multiple causes, such as overtreatment with anti-thyroid medications.

In cases of untreated hyperthyroidism, it has been associated on multiple occasions with maternal anemia, myopathy, heart failure, preeclampsia, placental abnormalities, hemorrhage during childbirth….

Can thyroid problems in pregnancy be prevented?

There are some guidelines to try to prevent and avoid thyroid gland diseases:

  • Women planning to become pregnant should be screened beforehand.
  • Pregnant women with goiter family history of thyroid problems or with anti-thyroid antibodies in the blood should be tested.
  • Apply low doses of thyroid hormone in women close to subclinical hypothyroidism.
  • In women who have anti-thyroid antibodies can receive selenium supplementation.

Treatments for thyroid problems during pregnancy

At the level of mild hyperthyroidism, it can usually be controlled by monitoring without needing treatment, as long as both mother and baby are in good health.

When hyperthyroidism is severe enough to need treatment, antithyroid medications are usually used. Prolithiouracil (PTU) is usually the appropriate medication. The goal of this treatment is to preserve maternal free T3 and free t4 levels using the lowest possible dose of medication. If the desired goals are achieved, the baby will have less risk of developing hypothyroidism. It is important to follow up the treatment closely.

In patients who for some reason (e.g. allergy) with antithyroid medications, surgery is presented as an alternative, although surgery is rarely recommended in pregnant women, due to the risk of surgery and anesthesia for both the baby and the mother.

Iodine is contraindicated for treating hyperthyroidism during pregnancy, as it can cross the placenta and be taken up by the baby’s thyroid, which may develop the disease as well.

To treat palpitations and tremors, beta-blockers can be used. Although they should be used with great care, as there is a link between a delay in the growth of the fetus associated with the consumption of these drugs.

In the case of hypothyroidism, the treatment is the adequate replacement of thyroid hormone through synthetic hormone. In women with hypothyroidism, thyroid function should be measured as soon as possible, and these should be repeated every six weeks to make sure that everything is working properly during pregnancy. As soon as the child is born, the usual dose of levothyroxine can be resumed.

Which specialist treats thyroid problems during pregnancy?

There are two specialists who work side by side when it comes to diagnosing, treating and following thyroid problems during pregnancy, and they are the Endocrinologist and the Gynecologist.