Q.1: What parameter to order and then how
to interpret the Lab reports?? Ans:- Free T4: Why Free FT4? Ans:-If no such evaluation was done prior to
conception as is often observed in our country then ,Free T4 should be done as a minimum .
However , if one order for TSH, TT4 (or Free T4) & TT3 (free T3)
as is most commonly done in private
sector whatever the reports come we have to
remember that there are some obvious
physiological changes in early preg which is due to gestational hyperthyroidism and reports
have to be evaluated in the context of physiological changes as we do in case
of hematocrit in preg .
Q. 2 : What are the physiological changes
in pregancy??
Ans:-There are some physiological changes in early preg. For instance,
there is rise of thyroid-binding Globulin (TBG) from liver à
as an effectà
serum T4 & T4 levels are increased, to compensate such increased secretion
of TBG from liver. However levels of FT4 changes minimally.
To sum up :--
A)
TBG production in liver is increasedà so T3 & T4 rise.
B)
What about Fee T4-Can we rely on that
parameter?? Yes, Very much. The only parameter of TFT (Thyroid Function Test)
which is not at all changes or say minimally
altered in early pregnancy is Free T4 .
As HCG (a glycoprotein) has thyrotrophic activityà The receptors of TSH has
structural similarity with that of hCG , so hCG stimulated rise of TSH is
common as is in tis case possibly .
Q. 3: What
about TSH-the commonly performed TFT (Thyroid Function Tets) in our country for
economic constraints. Serum TSH usually falls a little but occasionally
TSH may rise. As such, I personally don’t order TSH alone if she was never assed in last one
yr prior to conception.
Q. 5: Suppose pregnant
woman comes to us and she is from affluent class? In such a women it will be
prudent to insist on all the four tets of TFT(Thyroid Function Tets, like FreeT4, Free T3, TSH, Anti TPO ab, TSH
receptor stimulating antibodies to avoid repeated venepuncture .This last one
is a marker for Graves diseases. Thyroid-Stimulating
Immunoglobulin (TSI) Level what is a TSI test? TSI stands
for thyroid stimulating
immunoglobulin. TSIs are
antibodies that tell us that thyroid gland is more
active and release excess
amounts of thyroid hormone into
the blood. A TSI test measures the
amount of thyroid
stimulating immunoglobulin in her blood
What to do?? Clinicians,
therefore take advantage of FT4 –which is an excellent working parameter in
early preg-if thyroid status was not assessed preconceptionally.
TSH alone may occasionally (not always) misguide us:
What changes do occur physiologically in serum TSH in early preg?? As HCG has
thyrotrophic activity as well there will be rise of T4 from T. Gland à so serum TSH usually falls a
little but occasionally TSH may rise also.
In some cases temporarily fall may be too much (physiological fall) à even we can falsely level
them as “hyperthyroidism (gestational hyperthyroidism) ”-. But such low TSH (if
only one parameter of Thyroid is assessed) in most cases is to be considered as
physiological drop of TSH in early pregnancy. Therefore TSH alone will supply
us minimal information about thyroid status. However, in third trimester TSH
may increase upto 7. .However universal screening of TSH in neonates have been
in vogue for couple of years in our country too?
What is the serum TSH level in nonpregnant
state in women residing in Northern India?? In Sub-Himalayan belt? –there is almost universal
increase of TSH levels (most of men and women) due to Chr iodine deficiency.
Therefore in North Bihar, Uttarakhand, Assam , West Bengal in nonpregnant state
we hesitate to initiate replacement Ry unless TSH is > 10 and or other lab
parameters support to initiate T4 therapy.
The adjustment of dose is made by levels of T4 &
T4 and not by TSH was the practice earlier.
Q. 5: What about Postpartum period?? Postpartum period is very vital as sometimes patient herself withdraw the
drug of her own -- as she is convinced
in early peg is beneficial for brain dev of
her foetus. As such compliance may be lost after confinement -à sudden deterioration due to withdrawal of
drug Involving TSH, FT4 & FT3 serum levels –baffling the clinician.
Therefore, what tests to order if there is
no financial constraint?? In
my opinion one should insist on biochemical assay of FT4, (the most informative
parameter) & if fund permit than may ask for FT3, TSH & TPO ab also.
The take home message is that in preg TSH alone gives us poor information as it
may rise or fall as an effect of preg.
If she is a case of Hyperemesis or sick for any other medical disease in early pregancy à then TSH will be temporarily low but Ft4 will be temporarily high. So it will not be prudent to test for thyroid function when someone is very sick
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