Non-thyroidal illness and pregnancy

Question 1

what do thyroid hormone levels look like in non-thyroidal illness

Answer 1

TSH can be suppressed acutely then rise on recovery
tT3 fall due to impaired hepatic uptake and T4 to T3 conversion
fT4 usually stays within reference range or is moderately raised
can mimic TFTs seen in patients with thyroid disease
in patients recovering from illness, raised TFTs may be misinterpreted as hypothyroidism
low T3 may be an adaptive response

Question 2

what does non-thyroidal illness affect

Answer 2

thyroid binding proteins, which reduces total hormone and raises free hormone fraction

Question 3

should TFTs always be performed

Answer 3

no, should not be performed in patients with chronic or acute illness unless thyroid disease is considered to be the cause of the presenting complaint

Question 4

what is the severity and duration of the disease correlated with

Answer 4

degree of abnormality observed in TFTs

Question 5

what is the mechanism of TSH supression

Answer 5

TRH release is suppressed by cytokines and glucocorticoids (some drugs may also inhibit this)
carbohydrate residues on TSH dictate is biological activity and half-life, in NTI the carbohydrate moieties are modified leading to diminished bioactivity
in illness, thyroid hormone uptake by the liver is impaired, resulting in low circulating tT3
conversion of T3 to T4 be deiodinases is impaired in NTI so T3 levels fall

Question 6

thyroid hormone requirements in pregnancy

Answer 6

foetus needs T4 from week 4/5
uses maternal T4 exclusively up to week 10, and partially thereafter
T4 requirements can increase by 50% by week 20, and plateau from there

Question 7

what management is there for a pregnant woman with hypothyroidism

Answer 7

increase T4 dose when pregnancy is confirmed
TFTs in each trimester
check TFTs pre-pregnancy in autoimmune disease, current or PH/FH of thyroid disease, features of thyroid disease

Question 8

what is overt untreated hypothyroidism associated with

Answer 8

infertility
micarriage
pre-eclampsia
premature delivery
increased foetal mortality
impaired neurological development

Question 9

what is mild subclinical hypothyroidism associated with

Answer 9

neurodevelopmental delays
placental abruption