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Guidelines to Manage Thyroid During Pregnancy
 The
guidelines for the management of thyroid
disease during pregnancy and
after birth has been recently updated from its 2007 version. The clinical
practice guideline, published in the August issue of the Journal of Clinical
Endocrinology and Metabolism, recommend approaches to diagnosing and
treating patients with thyroid-related medical issues before, during, and
immediately after pregnancy.
Thyroid function tests change during pregnancy due to the influence of two main
hormones: human chorionic gonadotropin (hCG), the hormone that is
measured in the pregnancy test and estrogen, the main female hormone. For
the first 10-12 weeks of pregnancy, the baby is completely dependent on the
mother for the production of thyroid
hormone. By the end of the first trimester, the baby’s thyroid begins to
produce thyroid hormone on its own. The baby, however, remains dependent on the
mother for ingestion of adequate amounts of iodine,
which is essential to make the thyroid hormones.
The new clinical guideline include:
-
Trimester-specific reference ranges for pregnant women,
using a free T4 assay.
"The non-pregnant total T4 range
(5–12 μg/dL or 50–150 nmol/liter) are to be adapted in the second and third
trimesters by multiplying this range by one and a half-fold. For more, click
here.
-
Propylthiouracil
(PTU) should be the first-line drug for treatment of hyperthyroidism during the
first trimester of pregnancy. Methimazole (MMI) may also be prescribed if PTU is not available or not
tolerated. Clinicians should change treatment of patients from PTU to MMI after
completion of the first trimester because of the potential for liver toxicity.
-
Breast-feeding mothers should maintain a daily intake of 250 μg iodine to
ensure breast-milk provides 100 mg iodine per day to the infant.
-
One-daily prenatal vitamin containing
150 to 200 μg iodine needs to be consumed in the form of potassium iodide or
iodate, to protect from iodine deficiency.
-
 Thyroid receptor antibodies need to be measured before 22 weeks' gestational age
in mothers with "1)
current Graves' disease; or 2) a history of Graves' disease and treatment with
or thyroid-ectomy before pregnancy; or 3) a previous neonate with Graves'
disease; or 4) previously elevated [thyroid-stimulating hormone receptor
antibodies (TRAb)]," according to authors of the study.
-
Regular Fetal Screening: In
women with TRAb at least 2- to 3-fold the normal level, and women treated with
anti-thyroid drugs, fetal thyroid dysfunction should be screened for during the
fetal anatomy ultrasound done in the 18th–22nd week and repeated every four to
six weeks or as clinically indicated. Evidence of fetal thyroid dysfunction
could include thyroid enlargement, growth restriction, hydrops, presence of
goiter, advanced bone age, tachycardia, or cardiac failure.
-
Women with nodules from 5 mm to 1 cm in size should be considered for
fine-needle aspiration (FNA) if
they have a high risk history or suspicious findings on ultrasound, and women
with complex nodules from 1.5 to 2 cm in size should also receive an FNA.
"During the last weeks of pregnancy, FNA can reasonably be delayed until after
delivery. Ultrasound-guided FNA is likely to have an advantage for maximizing
adequate sampling," according to the study. In an FNA, a very fine, thin needle
is inserted into the thyroid, and aspirates (or "suctions") cells and/or fluid
from a thyroid nodule or mass into the needle. The sample obtained can then be
evaluated for the presence of cancerous cells.
The committee could not reach a consensus on screening recommendations for all
newly pregnant women. Some members recommended screening of all pregnant women
for serum TSH abnormalities by the ninth week or at the time of their first
visit.
Ref:
Dated 20 August 2012
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