Thyroid Disease in Pregnancy

Question 1

what hormones cause increased thyroid hormones in the blood during pregnancy

Answer 1

hCG - similar to TSH in that it stimulates the thyroid to produce more thyroid hormones

oestrogen - increased levels produces higher levels of TBG (protein that transports thyroid in the blood), this means there are less free thyroid hormones, which stimulates TSH

Question 2

hCG

Answer 2

produced by the palcenta after implantation

Question 3

thyroid hormones and neonatal development

Answer 3

maternal thyroxine is critical for neonatal development and growth

• linked to growth hormone function and production
• involved in myelinogenesis (proliferation of myelin sheaths) and axonal growth of nerves

Question 4

where do the foetus’ thyroid hormones come from

Answer 4

during the 1st trimester the foetus depends on the mothers supply of TH. this correlates with the rise in hCG which acts like TSH

at 12 weeks (trimester 2), the baby’s thyroid begins to function on its own, this correlates with the rise in TSH

Question 5

what are the consequences of increased demand on the thyroid during pregnancy

Answer 5

TBG protein increases

thyroid gland enlarges slightly

Question 6

what can happen if someone who is hypothyroid becomes pregnant

Answer 6

the thyroid cannot meet the increased demands

• thyroxine dose must be increased by 25 mcg as soon as pregnancy is suspected

TFT checked monthly for the first 20 weeks and then 2 monthly until term

Question 7

what TSH level should be aimed for in pregnancy to prevent hypothryoidism

Answer 7

<3 mU/L

Question 8

hCG

Answer 8

produced by the placenta after implantation - like TSH acts to stimulate the thyroid gland to produce more thyroid hormone and suppress TSH

Question 9

compare the chemical composition of hCG to TSH

Answer 9

chemically similar, have identical a chains but different ß chains

Question 10

what are the risks of untreated hypothyroidism in pregnancy

Answer 10

increased abortion

preeclampsia

abruption

post partum haemorrhage

pre term labour

foetal neuropsychological development impaired

Question 11

preeclampsia

Answer 11

sudden onset high BP and presence of protein in urine

Question 12

placental abruption

Answer 12

Placenta partially or completely separates from the uterus before the baby is born – deprive of oxygen and nutrients and cause severe bleeding

Question 13

pre term labour

Answer 13

regular contractions of the uterus that results in changes in the cervix, starting before 37 weeks

Question 14

compare the IQ of children with mothers who have untreated hypothyroidism to normal

Answer 14

average IQ of 7 points less

Question 15

complications of hyperthyroidism in pregnancy

Answer 15

infertility

spontaenous miscarriage

still birth

thyroid crisis in labour

transient neonatal thyrotoxicosis

Question 16

causes of thyrotoxicosis in pregnancy

Answer 16

Grave’s

TMNG, toxic adenoma

thyroiditis

Question 17

autoimmune diseases in pregnancy

Answer 17

often seen to improve during later pregnancy due to generalised suppression of the immune system (so that the foetus is not rejected) - immune privilege?

post partum thyroid dysfunction is common due to aggravation of autoimmune condition after parturition

Question 18

hyperemesis gravidarum

Answer 18

hyperthyroidism in pregnancy that is characterised by severe nausea, vomiting, weight loss and dehydration

it is believed to be triggered by high levels of hCG, which stimulates TSH receptor causing increased T3/4 and subsequently decreased TSH

tends to go away during second half of pregnancy

Question 19

what can high levels of hCG also lead to

Answer 19

transient hyperthryoidism that goes away during the second half of pregnancy

Question 20

how can hyperthyroidism be distinguished from the transient thyrotoxicosis assoicated with hCG

Answer 20

in HG:

• increased hCG and decreased TSH
• no TRAb antibodies (Grave’s)
• resolves by 20 weeks gestation, only treat if it persists past this point

Question 21

how is hyperthyroidism managed in pregnancy

Answer 21

it can be difficult to distinguish HG from hyperthyroidism so wait and see (provide supportive management) - HG will settle around 20 weeks gestation

prescribe ß blockers if needed

low dose anti-thyroid drugs - however wait as late as possible

Question 22

what anti thyroid drugs are prescribed

Answer 22

1st trimester - PTU (propythiouracil)

2nd/3rd trimester - carbimazole

Question 23

PTU risk

Answer 23

liver toxicity

best avoided, however ok in the 1st trimester

Question 24

CBZ risks

Answer 24

can cause embryopathy in the 2/3 trimester

causes scalp, GI etc abnormalities

choanal atresia and oesopahgeal atresia

Question 25

TRAb antibodies in pregnancy

Answer 25

TRAb antibodies can cross the placenta and cause transient neonatal hyperthyroidism

must be checked during pregnancy, especially in the 3rd trimester

• if present alert a neonataologist

Question 26

post partum thyroiditis

Answer 26

phenomenon following pregnancy

often transiently hyperthyroid, and then become hypothyroid

can also just cause hyper or hypo thyroidism

Question 27

how common is post partum thyroiditis

Answer 27

occurs in 5% of women

25% of those with T1DM

can occur up to one year post partum

25% persist hypothyroidism after one year

Question 28

what causes post partum thyroiditis

Answer 28

it is believed to result from the modifications of the immune system during pregnancy

there is a lymphocytic infiltration histologically

Question 29

outcome of post partum thyroiditis

Answer 29

self limiting normally

1 in 5 will develop permanent hypothyroidism requiring life long treatment

Question 30

what physical changes to the thyroid gland are there during post partum thyroiditis

Answer 30

small, diffuse and non tender goitre

Question 31

what is the hypothyroid phase of post partum thyroiditis associated with

Answer 31

post natal depression - may be misdiagnosed as this

TFTs are important in this situation obvs