Thyroid and Pregnancy

Thyroid disease in pregnancy comprises conditions that affect both the mother and the fetus with potential important consequences for child development.1 To inform the debate concerning the importance of thyroid disorders in pregnancy and the role of screening for thyroid function, it should be noted that the gestational incidence of hyperthyroidism is 0.20.3%, hypothyroidism 2.5% and thyroid antibody (mainly TPOAb) positivity around 10%.2 Pregnancy has marked effects on thyroid physiology and autoimmune thyroid disease tends to ameliorate through gestation due to general immunosuppression seen in pregnancy. The presence of thyroid antibodies is associated with infertility and miscarriage.3 The explanation for these findings is unknown and, unfortunately, thyroxine treatment in the euthyroid woman does not increase pregnancy rates.4Transient gestational hyperthyroidism due to elevation in HCG – a weak thyroid stimulator- is common and presents as hyperemesis gravidarum.5 It more frequent in multiple pregnancies and in hydatidiform mole but normally does not require therapy. Around 5% of women require hospitalisation becauseof ketosis and dehydration. They have an increased incidence of high thyroid hormone levels and suppressed TSH. The TSH receptor antibody should be measured if there is diagnostic confusion between hyperemesis and Graves’ disease.As mentioned, hyperthyroidism in pregnancy - usually due to Graves’ disease - is not common; untreated or poorly managed disease may result in miscarriage, pre term delivery, hypertension and pre eclampsia in the mother and intra uterine growth retardation and even increased death rate in the fetus. In a compliant patient, a good outcome can be expected both for mother and child if treatment with anti-thyroid drugs (propylthiouracil is preferred because of the association of methimazole with aplasia cutis and methimazole embryopathy) is instituted.6TSH receptor antibody should be measured at 36 weeks in such patients in order to predict the possibility of neonatal hyperthyroidism. Available evidence suggests that there is no significant effect of antithyroid drugs in utero on the long-term health of the neonate or child7 even if the dose during gestation has caused iatrogenic fetal hypothyroidism.8 Radioiodine therapy is contraindicated in pregnancy but thyroid surgery may be performed safely in the 2nd trimester.