Thyroid Disease & Pregnancy

Question 1

Physiology

Answer 1

• Fetal thyroxine is wholly obtained from maternal sources in early pregnancy as fetal thyroid gland becomes functional at 12 weeks
• Thyroxine is essential for fetal neurodevelopment
• In pregnancy, iodide losses through urineand the feto-placental unit contribute to a state of relative iodine deficiency
• Pregnant women require additional iodine intake - 250µg

Question 2

Effects of pregnancy on thyroid function

Answer 2

• Totsal thyroid hormone concentrations in blood are increased in pregnancy, partly due to high levels of oestroegen and due to the weak thyroid stimulating effects of hCG that acts like TSH
• Thyroxine (T4) levels rise from about 6-12 weeks, and peak by mid-gestation; reverse changes are seen with TSH
• Measure free T4 as it is only the free portion that can enter cells and modify metabolism

Question 3

Thyroid hormone ranges

Answer 3

Question 4

Fetal thyroid

Answer 4

• Fetal thyroid gland develops 7-9 weeks
• Placental transfer of T4 prior to 12 weeks
• From 12 weeks fetal thyroid function independent (in presence of adequate iodine)

Question 5

Effects of thyrotoxicosis on pregnancy

Answer 5

• Increase miscarriage
• Increase IUGR
• Increase preterm delivery
• Increase perinatal mortality

Question 6

Management

Answer 6

• Similar to non-pregnant
• Radioactive iodine contraindicated