Thyroid disorders in pregnancy and postpartum

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Thyroid disorders in pregnancy and postpartum SUMMARY Thyroid dysfunction in pregnancy has consequences for mother and baby.Potential problems include pre-eclampsia, prematurity and congenital abnormality.For women known to have hypothyroidism, an increase in thyroxine dose by 20-40% when pregnancy is confirmed usually ensures they remain euthyroid.Treatment of subclinical hypothyroidism is recommended if the woman has antithyroid antibodies.Treatment of hyperthyroidism, unless it is related to human chorionic gonadotrophin, involves propylthiouracil in the first trimester.Carbimazole may be used in the second trimester.Thyroid function tests are checked every month and every two weeks following a change in dose.Women with a current or a past history of Graves' disease who have thyrotropin receptor antibodies require early specialist referral as there is a 1-5% risk of fetal hyperthyroidism.Women with thyroid disorders in pregnancy should be followed up by their GP in the postpartum period.Postpartum thyroiditis may present months after delivery. PhysiologyDuring pregnancy the thyroid gland undergoes hyperplasia and increased vascularity.Circulating iodine is reduced and thyroid-binding globulin increases.The rising concentration of beta-human chorionic gonadotrophin (HCG) in the first trimester can directly stimulate the thyroid stimulating hormone (TSH) receptor as HCG has structural similarities to TSH.This in turn leads to increased free triidothyronine (fT3) and free thyroxine (fT4), suppressing TSH secretion.A serum TSH below 0.1 mIU/L may be present in 5% of women by the 11th week of pregnancy.