What is autoimmune thyroiditis during pregnancy?
Autoimmune thyroiditis (Hashimoto thyroiditis) is the main cause of spontaneous hypothyroidism. Autoimmune (from Lat. Auto – its, itself) diseases occur when the immune system is unable to recognize the tissues of its own organism from “alien”, while autoantibodies to the tissues of the thyroid gland (antibodies to thyroid peroxidase and thyreoglobulin) are formed in the body.
Pathogenesis during autoimmune thyroiditis during pregnancy
In autoimmune thyroiditis, when the thyroid gland is affected by an autoimmune process, its additional physiological stimulation that occurs during pregnancy may not reach its goal and, as in the situation with iodine deficiency, women will not experience an increase in thyroid hormone production, which is necessary for adequate fetal development in the first half of pregnancy. Moreover, overstimulation of the altered thyroid gland in autoimmune thyroiditis can lead to the manifestation of hypothyroidism during pregnancy. However, not every increase in the level of antibodies to thyroid peroxidase indicates the presence of autoimmune thyroiditis and the existing risk of developing hypothyroxinemia. In the general population, for every 10–30 adult women, there is 1 case of autoimmune thyroiditis. If the frequency of clinically overt autoimmune thyroiditis is 1-1.38%, then the presence of antibodies to peroxidase is detected in 10% of cases in healthy women. Researchers in recent years have found that autoimmune mechanisms are inherent not only in chronic autoimmune thyroiditis, but also in other types of thyroiditis, previously described as an independent disease.
Symptoms of Autoimmune thyroiditis during pregnancy
In the euthyroid phase and the phase of subclinical hypothyroidism, there are no symptoms. In some relatively rare cases, an increase in the volume of the thyroid gland (goiter), which rarely reaches significant degrees, comes to the fore in the euthyroid phase.
Diagnosis of autoimmune thyroiditis during pregnancy
Diagnostic criteria, in identifying a combination of which for a pregnant woman, it is advisable to prescribe preventive replacement therapy with L-thyroxine, are:
- increased levels of antibodies to thyroid peroxidase;
- an increase in the level of TSH in early pregnancy of more than 2 IU/l;
- increase in the volume of the thyroid gland more than 18 ml according to ultrasound.
Diagnosis of hypothyroidism during pregnancy can be difficult, as even in its normal course, women often have a feeling of cold, irritability or depression, and hair loss. Blood tests for the level of TSH, thyroid hormones, and antibodies to the thyroid gland are of fundamental importance for diagnosis. Due to the fact that the carriage of antibodies to thyroid peroxidase has no clinical manifestations, it is necessary to screen for this pathology before 12 weeks of pregnancy. If an increased level of antibodies to thyroid peroxidase is detected without other signs of autoimmune thyroiditis, a dynamic assessment of thyroid function during pregnancy (in each trimester) is necessary. As mentioned above, a low level of TSH is normal for early pregnancy. If the level of TSH in carriers of thyroid peroxidase antibodies is 2 mU/l, the prescription of L-thyroxine is not shown, with TSH over 2 mU/l in early pregnancy in women carrying these antibodies indirectly indicates a decrease in thyroid functional reserves and an increased risk development of relative hypothyroxinemia, and for such patients it is advisable to consider the appointment of preventive therapy for L-thyroxine. If the level of TSH exceeds 4 IU/l, regardless of the presence or absence of antibodies, the patient is most likely to have hypothyroidism. These women are given L-thyroxine therapy throughout pregnancy, and it is carried out according to the principles described above. Many studies demonstrate that women with an increased level of antibodies to thyroid peroxidase, even without impaired thyroid function, have an increased risk of spontaneous abortion in early pregnancy. The pathogenesis of abortion today remains unclear. Probably, antithyroid antibodies are a marker of generalized autoimmune dysfunction, as a result of which a miscarriage occurs.
The main provisions of the recommendations of the Association of Endocrinologists for the diagnosis of autoimmune thyroiditis:
- The diagnosis of autoimmune thyroiditis can not be established only on the basis of data on palpation of the thyroid gland, as well as after the detection of an increase or decrease in its volume.\
- “Large” diagnostic signs, the combination of which will allow to establish the diagnosis of autoimmune thyroiditis, are:
– primary hypothyroidism (manifest or persistent subclinical);
– the presence of antibodies to thyroid tissue or ultrasound signs of autoimmune pathology.
- In the absence of at least one of the “large” diagnostic signs, the diagnosis of autoimmune thyroiditis is only probabilistic in nature.
Treatment of autoimmune thyroiditis during pregnancy
Specific treatment has not been developed, and today there are no effective and safe methods of influence on the autoimmune process developing in the thyroid gland, which could prevent the progression of autoimmune thyroiditis to hypothyroidism. With the development of hypothyroidism, levothyroxine replacement therapy is indicated.