- Thyroid hormones play a critical role
during pregnancy in maintaining the health of the baby as well as the mother.
- Two separate
trials were conducted in pregnant women, those with subclinical hypothyroidism and those with
results suggest that administering levothyroxine did not improve the IQs of
their babies or reduce preterm births or other negative outcomes.
trials were conducted on pregnant women who had two different clinical
conditions, subclinical hypothyroidism
. The drug called levothyroxine
tested to see if it improved the cognitive abilities of the babies born, or
reduced preterm births or reduced other negative outcomes. The results were published
in The New England Journal of Medicine
hypothyroidism and hypothyroxinemia are conditions that arise due to
fluctuations in the blood levels of thyroid hormones.
‘Subclinical hypothyroidism in pregnant women could lead to serious health problems in the mother and the unborn baby. Treating the condition using levothyroxine may not have positive outcomes.’
Gland-Thyroid Gland Loop
Thyroid hormones primarily regulate the body's metabolism and are responsible for
the proper development and differentiation of every cell in the human body.
The first step
in the cascade of events of thyroid hormone or thyroxine release starts with
the release of the thyrotropin-releasing hormone or TRH
from the brain's
. The release of TRH stimulates the release of the thyroid-stimulating
hormone or thyrotropin or TSH
from the pituitary gland.
hormone, thyrotropin then stimulates the production of thyroxine (T4)
followed by triiodothyronine (T3)
which then speed up
is maintained via a feedback loop
that involves the hypothalamus,
pituitary gland and the thyroid gland. Low levels of T3
in the blood cause the hypothalamus to release more TRH that in turn, stimulates the
release of more TSH to help to restore the levels of the hormones. Similarly,
high levels of blood thyroid hormones can exert a negative feedback temporarily
pausing the release of TRH and in turn TSH.
In certain circumstances and conditions, there could be
fluctuations in the thyroid hormone levels that can be caused by a disruption or defect in any part of
the process. While too much of the hormone in the blood could lead to
causing body functions
to speed up, too little of it can cause hypothyroidism
which slows down
many body functions.
Hypothyroidism, also known as underactive
or low thyroid is a condition characterized by low thyroid hormone or
in the blood. The symptoms are tiredness, depression and
weight gain. Untreated hypothyroidism during pregnancy can affect the growth
and intellectual development in the baby, usually known as cretinism.
can result due to
functioning of the gland - Primary hypothyroidism
stimulation of TSH from the pituitary gland - Secondary hypothyroidism
release ofTRH from the brain'shypothalamus - Tertiary
Primary hypothyroidism is the most common form of hypothyroidism and is
caused mainly by iodine deficiency.
Subclinical hypothyroidism (SCH)
a mild thyroid failure that occurs when the levels of thyroid-stimulating
hormone (TSH) are normal
but the thyroxine (T4) levels are in
the low range.
occurs when the levels of thyroid-stimulating hormone (TSH) are normal
thyroxine (T4) levels are in the low range.
conditions occur in pregnancy and is more predominant in South Asia. They could
be associated with adverse fetal neurologic effects including a
lower-than-normal IQ in offspring.
Also known as
L-thyroxine, levothyroxine is a synthetic form of the body's thyroid
and is used to typically treat hypothyroidism. It is
taken as an oral pill or through intravenous injection and is the treatment of
choice for people requiring lifelong thyroid hormone treatment. It is also used
to treat subclinical hypothyroidism. It is safe to use during pregnancy.
Treatment of subclinical hypothyroidism or
hypothyroxinemia with levothyroxine
to improve cognitive
function in children is a subject of ongoing debate and research.
trials were conducted to see if treatment of pregnant women with subclinical hypothyroidism or hypothyroxinemia with levothyroxine improved the IQ of
the baby or reduced preterm births or other negative outcomes. The results were published
in The New England Journal of Medicine
hypothyroidism was defined as a thyrotropin level of 4.00 mU or more per liter
and a normal free thyroxine (T4
) level (0.86 to 1.90 nanograms per
deciliter [11 to 24 pmol per liter]). Hypothyroxinemia was defined as a normal thyrotropin level
(0.08 to 3.99 mU per liter) and a low free T4
nanograms per deciliter).
included 677 pregnant women with subclinical hypothyroidism who underwent
randomization at a mean of 16.7 weeks of gestation, and 526 pregnant women with
hypothyroxinemia who underwent randomization at a mean of 17.8 weeks of
study participants were randomly assigned to receive levothyroxine
in separate trials.
team checked the thyroid function on a monthly basis and the dosage of
levothyroxine was titrated to attain a normal thyrotropin or free thyroxine
levels (depending on the trial). The primary outcome gauged was the IQ levels of the children
which were checked at 5 years of age (or at 3 years of age if the 5-year
examination was missing) or death at an age of less than 3 years.
- Subclinical hypothyroidism group: The median IQ score of the children was reported to be 97 (in
the levothyroxine group and 94 in the placebo group..
- Hypothyroxinemia group: The median IQ score was reported to be 94 in the levothyroxine
group and 91in the placebo group.
- The IQ levels and other neurocognitive or pregnancy
outcomes were not significantly different between the children of women
given levothyroxine and children of those who received a placebo.
results suggest that there is no benefit in treating women with subclinical
hypothyroidism or hypothyroxinemia during their pregnancies as it did not
show any significantly better cognitive outcomes in children.
- Treatment of Subclinical Hypothyroidism or Hypothyroxinemia in Pregnancy - (http://www.nejm.org/doi/full/10.1056/NEJMoa1606205?query=featured_home)
- Thyroid Disease and Pregnancy - (http://www.thyroid.org/thyroid-disease-pregnancy/)