Thyroid

Question 1

Changes in thyroid physiology in pregnancy

Answer 1

**Increase
**Thyroid hormone synthesis - transplacental transfer of maternal T4, foetus converts to T3 (T3 does not cross the placenta)
Increase in thyroid binding globulin
Increase in urinary iodine excretion
Increase in deiodinase activity in the placenta -> increase thyroid hormone metabolism

HCG -> thyrotropic activity -> as levels increase in early pregnancy, there is an appropriate reciprocal decline in TSH

Question 2

Prevalence of thyroid disorders in pregnancy

Answer 2

Question 3

Recommendations for Hypothyroidism in Pregnancy

Answer 3

• Women who are pregnant, breastfeeding or planning a pregnancy - iodine supplementation
• Test for hypothyroidism if: personal history thyroid disease, type 1 DM, symptoms of thyroid disease

**Overt hypothyroidism = treat
** I.e. TSH above reference range with low T4 or TSH > 10

Screening for sibclinical hypothyroidism or TPO antibiodies and treatment with thyroxine not recommended in pregnancy (or prior) - though subclinical hypothyroidism is A/W higher risk of preeclampsia
Treatment of TPO antibodies (present in up to 20% reproductive age women) in euthyroid women not recommended (does not reduce miscarriage)

**Known diagnosis of hypothyroidism prior to pregnancy
**Adjust levothyroxine dose to target TSH level in lower half of trimester specific reference ranges
Increase dose thyroxine to 20-30% as soon as pregnancy is confirmed
TFTs every 4 weeks with any dose changes

Question 4

Notes on pregnancy with history of previous Grave’s disease

Answer 4

• Should have TRAB level chacked early in pregnancy and around 18-22 weeks if initially elevated - increased risk of placental transfer and resulting foetal/neonatal hyperthyroidism/goitre
• Positive TRAB sntibodies - regular follow up with serial foetal ultrasounds and postnatal TFTs

**Treatment of Grave’s disease in pregnancy
**PTU is planning pregnancy and first trimester. Can switch to carbimazole after 16 weeks
Carbimazole more potent, switching may increase risk of maternal or foetal hypothyroidism but PTU more hepatotoxic
At time of transition TSH and T4 should be monitored every 2-6 weeks

Question 5

Notes on hyperthyroidism in pregnancy

Answer 5

• 0.4% pregnancies, most commonly Grave’s and gestational thyrotoxicosis
• Gestational and hCG mediated thyrotoxicosis usually less severe than Grave’s thyrotoxicosis
• Usually runs a self limited course and rarely requires antithyroid drug treatment