Thyroid Disease in Pregnancy Flashcards
what hormones cause increased thyroid hormones in the blood during pregnancy
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
hCG
produced by the palcenta after implantation
thyroid hormones and neonatal development
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
where do the foetus’ thyroid hormones come from
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
what are the consequences of increased demand on the thyroid during pregnancy
TBG protein increases
thyroid gland enlarges slightly
what can happen if someone who is hypothyroid becomes pregnant
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
what TSH level should be aimed for in pregnancy to prevent hypothryoidism
<3 mU/L
hCG
produced by the placenta after implantation - like TSH acts to stimulate the thyroid gland to produce more thyroid hormone and suppress TSH
compare the chemical composition of hCG to TSH
chemically similar, have identical a chains but different ß chains
what are the risks of untreated hypothyroidism in pregnancy
increased abortion
preeclampsia
abruption
post partum haemorrhage
pre term labour
foetal neuropsychological development impaired
preeclampsia
sudden onset high BP and presence of protein in urine
placental abruption
Placenta partially or completely separates from the uterus before the baby is born – deprive of oxygen and nutrients and cause severe bleeding
pre term labour
regular contractions of the uterus that results in changes in the cervix, starting before 37 weeks
compare the IQ of children with mothers who have untreated hypothyroidism to normal
average IQ of 7 points less
complications of hyperthyroidism in pregnancy
infertility
spontaenous miscarriage
still birth
thyroid crisis in labour
transient neonatal thyrotoxicosis
causes of thyrotoxicosis in pregnancy
Grave’s
TMNG, toxic adenoma
thyroiditis
autoimmune diseases in pregnancy
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
hyperemesis gravidarum
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
what can high levels of hCG also lead to
transient hyperthryoidism that goes away during the second half of pregnancy
how can hyperthyroidism be distinguished from the transient thyrotoxicosis assoicated with hCG
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
how is hyperthyroidism managed in pregnancy
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
what anti thyroid drugs are prescribed
1st trimester - PTU (propythiouracil)
2nd/3rd trimester - carbimazole
PTU risk
liver toxicity
best avoided, however ok in the 1st trimester
CBZ risks
can cause embryopathy in the 2/3 trimester
causes scalp, GI etc abnormalities
choanal atresia and oesopahgeal atresia
