Thyroid function hormone concentrations change during pregnancy. There is also a reduction in antibody titre and an increase in T helper-2 (Th2) immune responses. Thyroid antibodies (TPOAb) are associated with an increased risk of miscarriage but levothyroxine administration can reduce both miscarriage and premature delivery rates. Gestational hyperthyroidism may be due to hyperemesis gravidarum or Graves disease. Management of Graves hyperthyroidism is with antithyroid drugs (propylthiouracil). TSH receptor antibodies should be measured to predict neonatal hyperthyroidism which may occur even when the mother is receiving thyroxine (T4) substitution therapy following previous therapy for Graves disease. Women receiving T4 for hypothyroidism should increase the dose by 50 micrograms per day when pregnant. Asympotmatic (subclinical) hypothyroidism occurs in up to 2.5% of women of whom 7080% will be TPOAb+ve. In such women T4 delivery to the fetal nervous system may be inadequate with significant consequences for subsequent childhood development. Screening for maternal hypothyroidism in early gestation with appropriate T4 therapy in hypothyroid women may prevent the decrement in child IQ. In post partum thyroid disease (PPTD) transient hyper and hypothyroidism occurs on a background of TPOAb+ve. The thyrotoxic phase is not very symptomatic (beta blocker only) but the hypothyroid phase requires T4 therapy. This should be given for one year before assessing whether post partum hypothyroidism has been permanent or transient.
Current recommendations for management are therefore:
1) Preconception counselling for those known to have thyroid disorders. 2) Focused targeted screening for thyroid function in early pregnancy, (known thyroid disease, diabetes mellitus type I, family history of autoimmune disorder, previous episode of postpartum thyroid disease). 3) Appropriate postpartum follow-up. Screening for thyroid function in early pregnancy should be advocated.
06 - 07 Nov 2006
Society for Endocrinology