Hyperthyroidism, hypothyroidism, Graves’ or Hashimoto’s disease… All of these thyroid pathologies, whether autoimmune or not, can have an impact on our ability to conceive a child and affect pregnancy. Explanations.

Located at the base of the neck, in front of the larynx and trachea, the thyroid is one of the largest endocrine glands in the human body at about 6 cm high and wide. Its role: by secreting the two thyroid hormones, thyroxine (T4) and triiodothyronine (T3), it is involved in the body’s metabolism, but also in brain growth and development. The secretion of these 2 key hormones takes place under the influence of TSH (or Thydroid Stimulating Hormone), a hormone of pituitary origin.

 Thyroid pathologies are the most common endocrine diseases in women of childbearing age. They can be schematically classified into 2 large groups that can have an impact on female reproductive health whether in the pre-conceptual, gestational or post-partum period:

• Hyperthyroidism is a thyroid disorder causing excess production of T3 and T4 hormones and less than normal secretion of TSH. Its most frequent symptoms: palpitations, thermophobia (hot flashes accompanied by sweating, redness, etc.), sometimes exophthalmos (the eyes seem to come out of their sockets), the appearance of a goiter, a loss of weight despite increased appetite and food intake, nervousness.
• hypothyroidism is for its part an imbalance at the origin of an insufficient secretion of thyroid hormones which is accompanied by a TSH level which is sometimes higher than normal. The signs that can be synonymous with hypothyroidism: muscle cramps, constipation, asthenia, fluid retention, excessive weight gain or even dry skin.

Thyroid pathologies can be linked to infertility, starting with hyperthyroidism, which affects 2,3% of women with difficulty conceiving (against 1,5% of the general female population). At issue: women with hyperthyroidism are more sensitive to GnRh (the hormone releasing the pituitary gonadotropin). This results in a greater secretion of luteinizing hormone (LH), itself responsible for an increase in estrogen levels. Menstrual cycle disorders can then appear and sometimes polymenorrhea (increased frequency of periods) making the onset of a natural pregnancy more complex, even if most women with hyperthyroidism retain ovulation. Treating hyperthyroidism can then improve the chances of pregnancy.

Hypothyroidism can also promote female infertility. Mainly responsible for the difficulties in conceiving: the abnormally high TSH level which can be the cause of oligomenorrhea (decrease in the intensity and frequency of periods), or even of amenorrhea and anovulation. In addition, this same rate would reduce the chances of successful pregnancy within the framework of a medically assisted procreation protocol. For these reasons, the American Thyroid Association has recommended maintaining the TSH level below 2.5 mU / l in women of childbearing age and wanting to have children.

As for hyperthyroidism, the first-line treatment to promote the chances of becoming pregnant in the event of hypothyroidism remains that of the said pathology.

Whether pre-existing or appearing during pregnancy, thyroid pathologies are carefully monitored. The most frequent endocrine diseases after gestational diabetes, they can indeed have significant consequences on the health of both mother and unborn child.

Hyperthyroidism

There are 3 very different types of hyperthyroidism in pregnant women:

• Transient gestational hyperthyroidism (TGA) affects up to 15% of pregnant women in their first trimester of pregnancy. Passenger, as its name suggests, this disorder is due to the gradual increase in the level of βHCG in the body which stimulates the thyroid (increase in the level of T4) and lowers the level of TSH. HGT is particularly noticeable in women who are pregnant with twins or who have vomiting during pregnancy. Benign, this hyperthyroidism generally disappears by itself at the beginning of the 2nd trimester of pregnancy and does not require any particular care, except in the case of severe vomiting where an exceptional and temporary treatment based on synthetic anti-thyroid drugs can be prescribed. .
• Graves’ disease is the cause of the vast majority of other hyperthyroidism. This can promote the onset of certain complications for mother and child, especially in the case of maternal anti-TSH receptor antibodies, such as:

  – prematurity,

  – growth retardation in utero,

  – fetal hyperthyroidism, anti-TSH receptor antibodies crossing the placental barrier,

  – a retroplacental hematoma,

  – pre-eclampsia, etc.

In view of these risks, treatment during pregnancy is therefore essential. The most advanced treatments based on radioactive iodine not being recommended during gestation, medication based on synthetic anti-thyroid drugs, beta-blockers as well as prophylactic measures (sick leave, rest, etc.) are therefore generally recommended. This treatment must however be the subject of special attention on the part of the practitioner, because it can induce, in the unborn child, an iatrogenic hypothyroidism (due to the treatment of the mother). In case of contraindications or ineffective treatment, thyroid surgery (total thyroidectomy) may be exceptionally recommended, only in the second trimester of pregnancy.

• Other hyperthyroidism are extremely rare. They can be due to very varied pathologies (mutation of the TSH receptor, molar pregnancy, toxic adenoma, subacute thyroiditis, etc.) which must be the subject of a specific diagnosis and management.

Hypothyroidism

Between 4 and 8% of pregnant women would have hypothyroidism. The disease then essentially has two origins: Hashimoto’s thyroiditis and iodine deficiency (in endemic areas). Sometimes difficult to detect in early pregnancy due to the physiological drop in peripheral hormone (T4) levels, hypothyroidism is also closely monitored during pregnancy if risk factors or medical history exist. The main complication incurred (even if it is poorly evaluated today): a slowed down fetal neurological development, even therefore mental retardation in the child, and fetal hypotrophy (a small baby). Much more rarely, hypothyroidism is associated with a risk of retroplacental hematoma, preeclampsia or fetal distress. In addition, other obstetric risks (repeated miscarriages, premature childbirth, postpartum thyroiditis) would be incurred in women suffering from hypothyroidism and having developed anti-thyroid antibodies (case of autoimmune diseases).

However, this thyroid condition can be easily managed during pregnancy with L-thyroxine therapy.

Although they also remain rare, thyroid disorders can appear in the weeks following birth, especially in women with a history of this type of endocrine pathology. It is mainly a question of:

• a postnatal exacerbation of certain autoimmune diseases. Indeed, during pregnancy the mother’s immune response is naturally weaker to allow the body to welcome the future child. Result: some autoimmune diseases “go to sleep” for a few months, before making a comeback.
• postpartum thyroid syndrome: if its causes are still unknown, this transient and painless syndrome is characterized by a first phase of hyperthyroidism of one to 2 months, occurring within 3 months after childbirth, then a phase of hypothyroidism, about 6 months after birth. Sometimes associated with postpartum depression, this syndrome is transient, with normal thyroid function usually resuming after a year. However, it can presage a subsequent hypothyroidism (in the case of autoantibodies) which must therefore be monitored regularly.