Thyroid Disease and pregnancy

Question 1

what affect do hyper/hypo- thyroidism have on fertility?

Answer 1

both cause anovulatory cycles - reduced fertility

Question 2

what is maternal thyroxine for?

Answer 2

thyroxine important for neonatal development (especially CNS)

Question 3

what is the demand on the thyroid during pregnancy?

Answer 3

Increased demand on thyroid during pregnancy
Plasma protein binding increases
Increased demand on thyroid during pregnancy
o increase in size
o increased T4 production just to maintain normal concentration

Question 4

how should patients on thyroxine be managed?

Answer 4

will have relative thyroid deficiency because the thyroid can’t meet increased demands – needs increased thyroxine dose

Question 5

how should pre-existing hypothyroidism be managed in pregnancy?

Answer 5

• Unable to compensate for increase demand
• Increase thyroxine dose by 25mcg AS SOON AS pregnancy suspected
• Check TFTs monthly for first 20 weeks then 2 monthly until term
• The average dose increase is by 50% (e.g. from 100mcg to 150mcg) by 20 weeks.
• Aim for TSH <3 mU/l

If untreated
o Increased preeclampsia, abortion, abruption, postpartum haemorrhage and preterm labour
o Foetal neuropsychological development – child can have 7 IQ points less and an increased risk of an IQ <85

Question 6

what is the physiological effect pregnancy has on the thyroid?

Answer 6

HCG which is produced by the implanted ovum decreases TSH levels
Thyroxine (free T4) is high
HCG levels being very high also causes hyperemesis gravidarum

Excess hCG mimics hyperthyroidism biochemically and so it can be hard to differentiate
o Check for thyroid antibodies
o If hCG then it will resolve after 20 weeks
o Blood results often aren’t as severe also

Question 7

what are the risks of hyperthyroidism and pregnancy

Answer 7

infertility/ammenorrhoea 
spontaneous miscarriage 
stillbirth 
thyroid crisis in labour 
transient neonatal thyrotoxicosis

Question 8

how is hyperthyroidism managed in pregnancy?

Answer 8

Wait and see (supportive management)		
o if hyperemesis, will settle					
o Graves may settle as pregnancy suppresses autoimmunity			
o Check TRAB antibodies
B-blockers if needed

LOW DOSE anti-thyroid drugs
o Propylthiouracil 1st trimester (risk of liver toxicity and don’t use after 1st trimester)
o Carbimazole 2/3rd trimester
- Can cause embryopathy in 1st trimester
- Scalp abnormalities
- GI abnormalities
- Choanal and oesophageal artesia
o wait as late as possible – could always be hCG effects
Check TRAb antibodies during pregnancy (ideally third trimester) - If present alert neonatalogist
TRAb antibodies can cross the placenta and cause neonatal transient hyperthyroidism

Question 9

what is post partum thyroiditis?

Answer 9

after delivery mother develops transient thyroiditis classically at 6 weeks
then at 3 months underactive thyroid develops

Question 10

how is post partum thyroiditis managed?

Answer 10

if hypothyroidism persists over a year then ongoing thyroxine is likely needed
hyperthyroid is not often treated but if symptomatic then the hypothyroid will be treated

Question 11

how does post partum thyroiditis present?

Answer 11

Small, diffuse, nontender goitre
Hypothyroid phase associated with postnatal depression
Postpartum - Exacerbation of all autoimmune dx