In this discussion, we’ll take a look at
the interaction between the mother and the
foetus and what may then happen when there
is lack of proper thyroid functioning between
the two symbiotic relationships.
Maternal thyroid changes during pregnancy.
Major alterations in the thyroid system during
pregnancy include the following.
Because of the estrogen, there will be an
increase in total binding globulin.
That increase in total binding globulin is
then going to remove or more accurately bind
the free T4.
You will then increase the bound type of T4
which then increases the total.
When the total T4 increases, remember that
the free is going to then communicate with
the hypothalamal pituitary axis and therefore
making sure that the free is always available
in the mother so that the foetus is properly
This is all perfectly normal during pregnancy
with thyroid functioning.
Also, as you can imagine because now, the
hypothalamus, pituitary and the thyroid is
increasing its production to normal levels
of free there will also be increased demand
Results from an increase in iodide clearance
by the kidney due to increased GFR that is
also noted in pregnancy and siphoning.
Meaning to say, the channelling of the iodine
from the mother to the foetus for proper thyroid
The thyroid gland can increase in size during
pregnancy called Pregnancy Induced Goiter,
perfectly normal especially though in a patient
from, let’s say, a developing country in
which there is already iodine deficiency…
We’re going to walk through this graph in
Let’s first dissect the graph like we’ve
done with every single one to clearly understand
as to what we’re trying to compare.
On the X-axis would be the weeks of gestation…
10, 20, 30, 40… takes us to all three trimesters.
And on the Y-axis represents your relative
serum concentration for the particular hormones.
The blue line is characterized by TSH, the
red line is then defined as being your hCG
and the grey shade represents TBG.
You can expect during pregnancy and we already
discussed over and over again that estrogen
that’s abundant in pregnant women then causes
increased total binding globulin and that
total binding globulin in a separate discussion.
How it’s going to bind to that free T4 and
so, therefore, the pregnant woman is then
going to normally have an enlarged thyroid
glands so that it can keep up with the free
T4 and that’s a different discussion that
we’ve had over and over again.
Here, in this discussion is the fact that
we’re going to focus upon hCG and in the
first 8 to 10 weeks is when the placenta,
the syncytiotrophoblast of the foetus is producing
human chorionic gonadotropin.
Human chorionic gonadotropin apart from working
on the LH receptor of the corpus luteum so
that you bring out the progesterone for proper
foetal development is also working upon or
replacing the TSH, isn’t it?
And it’s perfectly normal to find a little
bit of a drop in TSH during pregnancy, hence
the dip that you noticed and the elevation
of hCG this whopping interaction.
Everything’s perfectly normal though.
Meaning to say, that you have normal production
of your T3, T4.
And then you noticed after 10 weeks, especially
after 8 weeks you’re going to start dropping
your hCG and the TSH comes back to its normal
functioning upon your TSH receptors.
hCG… let’s read through this now, hCG
can weakly turn on the thyroid, but it can
be bind and transduce signalling from TSH
receptor; hCG and TSH are structurally very
High circulating hCG levels in the first trimester
may result in a slightly low TSH.
When this occurs TSH will be slightly decreased…
not every single pregnant woman, huh?
However, those of you that are going into
your wards and your shadowing your OB you
can expect that TSH in a normal pregnant woman
to be highly depressed, but as far as the
TSH is concerned that after the first trimester,
it comes back to be perfectly normal.
TSH the blue line, comes back to perfectly
In the meantime, tell me about that free T4.
It’s always at normal levels… always at
What about the bound?
Estrogen working upon the liver to increase
What about the total?
Total is mostly composed or contributed by
So, therefore, total is increased.
Let’s take a look at pregnancy and all the
different changes that are taking place overall.
It’s a nice little table here to give you
a summary of what you can expect in pregnancy
with all the different organ systems: thyroid
testing, TSH, Total T3, T4.
Finding first trimester… your TSH could
be a little bit depressed, that’s okay discussion
Because of Beta-hCG… we just discussed this
previously in that graph.
Finding of total is increased why, because
estrogen then works upon the liver to increase
Let’s move on to another system.
Cortisol… estrogen increases cortisol binding
globulin from the liver thus you find your
total to be elevated.
Your cardiovascular system is the following.
Now, you’ll find this to be fascinating
and I said review of your cardiovascular system
First, what happens is the fact that you’re
going to decrease your peripheral vascular
resistance, especially in the first trimester
by 50 percent.
Who’s helping you do this in pregnancy?
These hormones include progesterone and substances
such as nitric oxide.
Because of all this increase in plasma volume
during pregnancy, you’re going to find an
increase in cardiac output.
Here, once again, you find it to be increased
by 50 percent, increase in plasma volume decrease
in PVR; a decrease is your after load.
So, therefore, cardiac output increases as
much as 50 percent, the heart rate increases
Cardiovascular changes that are taking place
during pregnancy… the respiratory rate increases,
the plasma volume increases as much as 50
Now, RBC mass could increase as much as 20
to 30 percent.
I really want you to focus upon not much…
the discussion is a little bit more important
There might be haemodilution, in fact, there
is haemodilution because of that increase
in plasma volume that we just saw above so
even though there was an increase that could
be an increase in RBC mass, it’s really
the haemodilution that you’re also paying
attention to because of that increase in plasma
Thyroid hormone and the foetal development.
In the first trimester, the baby’s completely
dependent on the mother for the production
of thyroid hormone… the first trimester.
By the end of the first trimester, the baby’s
thyroid begins to produce its own thyroid
hormones, thus the siphoning of the iodine
from the mother to the foetus becomes incredibly
Impact on the mother… in women with subclinical
hypothyroidism, what does that mean to you?
Subclinical, meaning to say the mother and
even before she became pregnant never really
had overt hypothyroidism; subclinical would
mean that you have a normal free T4, but a
high TSH hence subclinical.
Extra demands of pregnancy can precipitate
clinical disease though.
Is that clear?
So, that’s when things become really interesting
Up until pregnancy, the patient was completely
asymptomatic, no bradycardia and no tiredness
or fatigue; in fact, the free T4 is perfectly
Now, she becomes pregnant, there’s increase
for demand for iodine, there’s increased
demand for thyroid hormones, in general.
She may then become symptomatic which becomes
dangerous for the foetus obviously and for
her as well.
Now, the overt maternal hypothyroidism is
typically not significant, the reason for
that is if your patient wishes to become pregnant
and she has Hashimoto to begin with, there’s
every possibility that with overt disease,
she’s already infertile.
So, what I’m saying is the reason that it’s
not significant is because pregnancy never
took place in overt maternal hypothyroidism.
Untreated hypothyroidism can lead to anaemia,
myopathy, heart failure, pre-eclampsia, placental
abnormalities, low birth weight babies, postpartum
haemorrhage… all kinds of issues as you
would expect with decreased thyroid hormone.
If that’s the impact on the mother by thyroid
hormones, what about the impact on the baby?
Thyroid hormone critical for development of
everything in the infant, especially during
the first two to three years of life.
So, there’s long term consequences.
Children with congenital hypothyroidism, no
thyroid function can have severe, severe developmental
abnormalities; you have to treat this child
immediately and promptly.
These abnormalities can be treated if-if screened
which is done in the U.S. diligently within
12 to 30 days after birth early.
Hence, all newborn babies in U.S. are screened
by for congenital hypothyroidism because you
have to be prompt with your treatment because
the long term sequelae could be disastrous,
if not administered properly.
If untreated, everything goes wrong.
The child, I showed you cretinism earlier,
there’s a protuberant stomach with umbilical
hernia, macroglossia, I wanted you to pay
attention to that cheek and the mouth, macroglossia.
IQ severely compromised and the skin is yellow.
Because of carotene.