[Pregnancy and the thyroid gland].

Thyroid disease is very frequent in women, particularly during pregnancy and the post partum period. Several mechanisms are involved. The most frequent is related to immunological modifications during pregnancy and increased risk of producing anti-thyroid autoantibodies. The second is related to a relative deficiency of iodine in France, aggravated by increased glomerular filtration during pregnancy. The third mechanism involves changes in thyroid hormone metabolism induced by pregnancy. Finally, the fourth mechanism is a purely hormonal phenomenon due to the possible stimulating effect of gonadotropic chorionic hormone on the TSH receptor. Thyroid disease requires special care for pregnant women or those desiring pregnancy. There are several reasons as it is difficult for thyroid hormones to cross the placental barrier after several weeks of gestation but antithyroid drugs, iodine and autoantibodies cross it easily. There is a risk of maternal and fetal complications in case of untreated hyperthyroidism due to Graves' disease. If the patient is treated prior to pregnancy, it is important to know the course and type of treatment used to attain euthyroidism because maternal anti-TSH receptor autoantibodies cross the placenta-blood barrier after surgery or radioiodine treatment and increase the risk of fetal and neonatal hyperthyroidism. If the woman is under treatment or if her Graves' disease begins during pregnancy, the course generally improves during the second trimester but worsens after delivery. Antithyroid drugs should be titrated regularly because of the risk of maternal or fetal hypothyroidism and subsequent risk for fetal development. In addition, antithyroid drugs have been suggested to have a teratogenic effect although this has not been formally demonstrated. Management is perturbed less in other hyperthyroidisms as pregnancy has less impact on the disease. Hypothyroidism is very uncommon during pregnancy. Depending on the etiology, maternal hypothyroidism can raise the risk of fetal hypothyroidism, requiring careful management due to the risk of mental sequelae and compressive goiter in the infant. For thyroid morphology diseases, the problem is generally one of differentiated thyroid cancer, particular as the frequency is probably higher during pregnancy, the course being aggravated by the TSH-like effect of hCG, and curative treatment with radioactive iodine which cannot be started unless there is no risk of pregnancy. Exploration of a thyroid nodule in a pregnant women is a particular situation as scintigraphy is not advisable prior to the fourth month for the technetium method and for the entire pregnancy for 123-iodine. Needle aspiration can be used systematically and the histology results help guide management. Inquiry into past thyroid history and physical examination are thus required for all pregnant women or women desiring pregnancy in order to choose the best management scheme.