115 - Thyroid and pregnancy
Autor(s): E. Toffalori, P. Caciagli
Issue: RIMeL - IJLaM, Vol. 6, N. 2, 2010 (MAF Servizi srl ed.)
Page(s): 115-121
During pregnancy normal thyroid activity undergoes significant changes. Few weeks after conception, serum TBG increases two- to three- fold. This leads to an increase in the total amount of thyroid hormones of 1,5 times greater than pre-pregnancy values. The serum fT4 and fT3 levels decrease below the normal mean in the second and third trimesters. This decrease is further amplified when the iodide nutrition status of the mother is restricted or deficient. In the first trimester the increased hCG concentration is associated to a decrease in serum TSH levels that may also reach 20%. The hCG ß-subunits has mild thyroid-stimulating activity, this leads to an increase in iodide uptake and thyroid hormone secretion with a TSH decrease. The renal cle arance of iodide increases and during pregnancy iodine intake should double. These changes can complicate the interpretation of maternal thyroid function tests. Management of thyroid diseases during pregnancy requires special consideration because can have adverse effects on the pregnancy and the fetus. Diagnosis of hyperthyroidism and Basedow disease can be difficult because healthy pregnant women may exhibit the same symptoms. Gestational hyperemesis usually not require treatment, has negative story and normal antibody antithyroid concentration. Both overt and subclinical hypothyroidism have adverse effects on the course of pregnancy and neural and intellectual development of the fetus. Thyroid diseases should be corrected before initiation of pregnancy, replacement dosage augmented and euthyroidism maintained. Assessment of thyroid function during pregnancy be done with a clinical valuation as well as measurement of TSH and fT4. Measurement of thyroid autoantibodies may also be useful in selected cases to detect maternal Basedow disease or Hashimoto thyroiditis and to assess risk of fetal or neonatal consequences of maternal thyroid dysfunction. Early diagnosis and treatment is important to prevent complications, so it is recommend case finding among the women at high risk for thyroid disease. In recent years several studies have demonstrated that the use of reference intervals of normal people for pregnant women leads to an underestimation of deficiencies in the maternal thyroid functionality with an high level of risk for both the mother and the neurological development of the fetus and child. The guidelines NACB 2006 specify that trimester-specific reference intervals should be used when reporting thyroid test values for pregnant patients and that fT4 and fT3 reference ranges in pregnancy are method-depend and should be established independently for each method.