non-thyroidal illness and pregnancy W6 Flashcards
what is non-thyroidal illness (NTI)?
any illness outside thyroid that is significant enough to impact pattern of thyroid hormone measurements
non-thyroidal illness thyroid hormone levels? why?
tT3 (total T3) falls due to impaired hepatic uptake and T4 to T3 conversion
illness affects thyroid hormone binding proteins which reduces total hormone and raises free hormone fraction
fT4 usually stays within reference or is modestly raised
severity and duration associated with degree of abnormality in TFTs
mechanisms of TSH suppression in NHI
TRH release suppressed by cytokines, glucocorticoids
drugs eg dopamine inhibit TSH release
carbohydrate moieties on TSH modified, leads to diminished bioactivity
thyroid hormone uptake in liver impaired, results in low circulating tT3.
conversion of T3 to T4 impaired so T3 levels fall
what do low levels of T3 indicate
NTI
what is T4 important for in the fetus
developing CNS
control growth and metabolism of fetus
untreated overt hypothyroidism in pregnancy associated with?
infertility, miscarriage
pre-eclampsia, premature delivery
increased foetal mortality, impaired neurological development
mild (subclinical hypothyroidism) associated with?
neurodevelopmental delays, placental abruption
how should hypothyroid patient on levothyroxine be treated during pregnancy
increase thyroxine dose instantly
check TFTs every trimester
patients with current/previous Graves should have TRAb checked at antenatal booking and pre-delivery
why must TRAbs be checked during pregnancy?
can cross placenta and act on the fetal thyroid gland by 20 weeks to cause neonatal hyperthyroidism
what does HCG induce? how should this be treated?
HCG induces transient hyperthyroidism as mimics actions of TSH.
symptomatic treatment
what type of hormones should you check in pregnancy and why?
free hormones, not total hormones
because oestrogen can increase amount of thyroid binding globulin
