Thyroid problems during pregnancy: should you be concerned?

Problème de thyroïde pendant la grossesse : faut-il s’inquiéter ?

Thyroid problems, hypo- or hyperthyroidism, are the cause of various symptoms that can be very disabling in many ways. We explain.

What is the thyroid?

The thyroid is a 20-gram gland located at the base of the neck. It is shaped like a butterfly, with a central part (isthmus), followed by a right and left lobe.

Benefits for the body

The thyroid is one of the largest endocrine glands. Its role is to secrete thyroid hormones: thyroxine (T4) and triiodothyronine (T3). These hormones regulate metabolism, body temperature, heart rate, the digestive and nervous systems...

In short: the thyroid really is your body's conductor. The menstrual cycle is therefore influenced by the thyroid (mood, sexual desire...).

TSH levels

Thyroid hormones are produced by a hormone from the pituitary gland called TSH (Thyroid Stimulating Hormone).

What role does the thyroid play during pregnancy?

The pregnancy is a time of upheaval for the thyroid gland. In fact, during this period, the thyroid increases its activity, as it has to produce even more hormones to ensure the growth and proper development of the fetus.

These thyroid hormones are produced by iodine. Pregnancy is a period when iodine deficiency is very frequent (part of it passes through the placenta to the fetus, while the rest is eliminated by the kidneys to an even greater extent in pregnant women).

This deficiency can lead to an enlargement of the thyroid gland, known as goiter. Fortunately, there are ways of reversing this phenomenon.

What is a normal pregnancy TSH level?

Defining the TSH level ensures that a person is not suffering from thyroid dysfunction. A thyroid that functions normally is called euthyroid. A normal TSH level is between 0.4 and 2.5 MUI/L during the first trimester of pregnancy. When it exceeds this threshold, we speak of hyperthyroidism. If it's too low, it's hypothyroidism.

Which thyroid disorders should be monitored during pregnancy?

During the first four months of pregnancy, the thyroid plays a very important role. It is responsible for ensuring the proper development of the foetus' brain, by supplying it with a sufficient quantity of hormones.

For this reason, thyroid activity in pregnant women is closely monitored. Regular monitoring will detect any disorders that could have harmful consequences for both mother and unborn child.


There are 3 types of hyperthyroidism in pregnant women.

Firstly, transient gestational thyroiditis, which affects 15% of pregnant women during their first trimester. It's a temporary condition, due to increased levels of BHCG in the body, which stimulates the thyroid (increasing T4) and decreases TSH.

Secondly, there is transient gestational hyperthyroidism, which is particularly noticeable in women who are pregnant with twins or who suffer from gravid vomiting. But don't panic: in most cases, this thyroid condition disappears at the start of the 2nd trimester of pregnancy, and no special treatment is required unless you're experiencing intense vomiting. In this case, treatment may be prescribed.

Graves' disease is the cause of the vast majority of hyperthyroidism disorders. It may be responsible for the development of certain complications for both mother and child, such as :

  • Prematurity;
  • in utero growth retardation
  • Fetal hypothyroidism, as anti-TSH receptor antibodies cross the placental barrier;
  • Pre-eclampsia;
  • Retroplacental hematoma.

Since these risks are present, it is very important to propose treatment by a health professional.

Other types of hyperthyroidism are rare, but can occur as a result of a wide variety of pathologies. They require special diagnosis and management.


An estimated 4% to 8% of women suffer from hypothyroidism. The disease has two origins:

  • Hashimoto's thyroiditis;
  • Iodine deficiency;

Unlike hyperthyroidism, hypothyroidism is often difficult to detect in early pregnancy. This is because peripheral hormone levels (T4) drop. Hypothyroidism is closely monitored if the pregnant woman has risk factors or a medical history. Hypothyroidism can lead to complications such as :

  • Neurological development, which may be slowed, leading to mental retardation in the child;
  • Or fetal hypotrophy;

Hypothyroidism may also be associated with a risk of retroplacental hematoma, preeclampsia or fetal distress.

Hypothyroidism can lead to obstetrical risks (recurrent miscarriage, premature delivery, post-partum thyroiditis).

What are the symptoms of a thyroid problem?

Several symptoms can herald a thyroid problem:

  • rapid and significant weight loss
  • Excessive sensitivity to heat;
  • Sudden thirst;
  • Hot flushes;
  • Excessive sweating;
  • Mood disorders ;
  • Pregnancy insomnia;
  • Hyperactivity;
  • Stress and anxiety;
  • Bulging eyes;
  • Enlargement of the neck, suggesting a goiter;
  • Increased frequency of bowel movements;
  • Pregnancy diarrhea;
  • Palpitations;
  • Reduced or absent menstrual periods.

When a patient presents symptoms suggesting thyroid dysfunction, her doctor will prescribe a thyroid check-up. The aim of this test is to check TSH levels.

How to treat thyroid problems in pregnant women?

Radioactive iodine-based treatments are not recommended during pregnancy. However, other treatments are available to restore hormonal balance: synthetic antithyroid drugs and beta-blockers. These treatments require careful monitoring. Time off work and rest are recommended.

What are the risks of thyroid disease for pregnancy and the baby?

Thyroid disorders are easily detected during the first trimester of pregnancy. There are no particular risks to report; the main risk remains the fetal risk, since the neurological development of the fetus is carried out by the mother-to-be's thyroid hormones until the 4th month of pregnancy.

For this reason, it's vital that the thyroid gland functions properly during pregnancy, especially in the first trimester, when the fetus develops via its mother's thyroid hormones. It's not until the 18th or 20th week of amenorrhea that the fetal thyroid becomes functional.

The risks are minimal, however, because as already mentioned, hypothyroidism is treated very quickly. If left untreated, or treated too late, the risk to the fetus is intellectual retardation.

Thyroid problems and fertility: is it possible to get pregnant?

Thyroid pathologies can indeed be linked to infertility, particularly in the case of hyperthyroidism (which affects 2.3% of women who have difficulty getting pregnant, 1.5% of the general female population).

Women suffering from hyperthyroidism are more sensitive to GnRh (the hormone that releases pituitary gonadotropin). This leads to greater production of luteinizing hormone (LH), which increases estrogen levels. This can lead to menstrual cycle disorders such as polymenorrhea (when the frequency of menstrual periods increases), making natural pregnancy more difficult. Despite this, women with hyperthyroidism still ovulate.

Hypothyroidism can also be a source of female infertility. The main cause of these difficulties in conceiving is the high TSH level, which can lead to oligomenorrhea (i.e. a reduction in the size and frequency of menstrual periods), amenorrhea or anovulatory cycles. It also reduces the chances of successful pregnancy in MAP procedures.

Thyroid and pregnancy FAQs

Does TSH increase during pregnancy?

During pregnancy, TSH levels generally drop during the first few months. This is a natural process of the thyroid glands, and does not mean that the mother is suffering from hyperthyroidism. Thereafter, TSH rises and returns to normal.

Can I take levothyrox during pregnancy?

Levothyrox (synthetic T4, a synthetic form of the hormone thyroxine) is safe for the fetus. We invite you to consult your doctor if you need information about treatments that may or may not be recommended during pregnancy. In any case, this medication is not available without a prescription.

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The information contained in the articles on is general information only. Although reviewed by health professionals, this information is not error-free, does not constitute health advice or consultation, and is not intended to provide a diagnosis or suggest a course of treatment. Under no circumstances may this information be used as a substitute for medical advice or consultation with a healthcare professional. If you have any questions, please consult your doctor.