Managing Thyroid Disorder during Pregnancy
disease is present in 2-5 percent of all women and 1-2 percent of
women in the reproductive age group. Thyroid problems are
common in women who are
pregnant. Several of the thyroid disorders which tend to occur during pregnancy are
autoimmune in nature. By this we mean that the body develops antibodies directed
against thyroid cells, which then affect the way the thyroid gland functions.
Antibodies which damage the thyroid cells may result in lymphocytic thyroiditis
(inflammation of the thyroid), also known as Hashimoto's disease. These damaging
antibodies can reduce the function of the thyroid and lead to
the other hand, your body can make antibodies against thyroid tissue which can
stimulate thyroid cell function. In this case,
hyperthyroidism due to
over-function of the thyroid (Graves' disease) may be the result.
Hypothyroidism. If hypothyroidism is suspected in a pregnant patient,
the physician can perform a TSH blood test. Just as in non-pregnant women, the
TSH will be increased if hypothyroidism is present. If a woman is already being
treated with thyroxine when she becomes pregnant, she should continue to take
this medication during pregnancy. Thyroxine is safe to take and is well absorbed
during pregnancy. Although there is usually no need for a dose change, some
women require somewhat higher doses when they are pregnant. Physicians generally
monitor the TSH level to detect even mild hypothyroidism and increase the
thyroxine dose, if necessary.
Guidelines for treatment
The following is a summary of the key components of the guidelines, which
have important implications for women who develop hypothyroidism
If a woman is diagnosed with hypothyroidism prior to pregnancy, her
thyroid medication should be adjusted so that the TSH level is no higher
than 2.5 µU/ml prior to becoming pregnant.
If a woman is
diagnosed as hypothyroid during pregnancy, she should be treated without
delay, with the goal of restoring her thyroid levels to normal as quickly as
possible. During the first trimester, the TSH should be maintained at less
than 2.5 µU/ml (and less than 3.0 µU/ml in the second and third trimesters.)
After initial diagnosis, thyroid function tests should be reevaluated within
30 to 40 days.
By the time a woman is four to six weeks pregnant, her dose of thyroid
medication will usually need to be increased, potentially by as much as 30 to
A woman with thyroid autoimmunity (such as she has previously tested
positive for thyroid antibodies) who has normal TSH levels in the early stages
pregnancy is still at risk of becoming hypothyroid at any point in the.
She should be monitored regularly through the pregnancy for elevated TSH.
most women with hypothyroidism will need their dosage of thyroid hormone
Hyperthyroidism. Thyrotoxicosis (hyperthyroidism) during pregnancy,
most often due to Graves' disease, or it can be a transient form that triggers
hyperemesis gravidarum –- a condition of pregnancy that causes severe
Guidelines for treatment
The risk of miscarriage and stillbirth is increased if thyrotoxicosis goes
untreated, and the overall risks to mother and baby further increase if the
disease persists or is first recognized late in pregnancy. The
suggested by specific physical
signs such as prominent eyes, enlarged thyroid
gland, and exaggerated reflexes, and is confirmed by markedly elevated serum
thyroid hormone levels.
Radioactive iodine scans or treatment
are never performed in pregnancy. However, if a thyroid scan is inadvertently
done in pregnancy, this should cause little concern, since the amount of
radioactivity delivered to the fetus is barely above the background level in the
environment. On the other hand, if radioactive iodine treatment is inadvertently
administered in pregnancy, this raises concerns about the radiation effects on
the developing fetus in
early pregnancy. The amount of radiation may approach
levels which can be harmful and, after appropriate counseling, some patients may
opt for a therapeutic abortion. Still a number of completely normal infants have
been born in this situation. Later in pregnancy radioactive iodine can destroy
the fetal thyroid, but this is probably not a sufficient reason to end the
pregnancy, since recognition and treatment of hypothyroidism shortly after
delivery usually assures normal growth and development in the
The treatment of choice for thyrotoxicosis during pregnancy is antithyroid
medication, either propylthiouracil or
methimazole, since radioactive iodine
cannot be used. The initial goal is to control
the hyperthyroidism and then use the lowest medication dose possible to maintain
the serum thyroid hormone levels in the high normal range. In this way the
smaller doses of medications are used, and there seems to be little risk to the
baby. If a mild allergy to one of these medications develops, the other
medication may be substituted. If there is a problem with taking pills or more
severe drug allergy, then an operation may be performed to remove most of the
thyroid gland. This is usually done in the middle part of the pregnancy.
Fortunately, it is rarely necessary.
The natural course of hyperthyroidism in pregnancy is for the disease to
become milder or remit totally near term. In many patients anti-thyroid
medications can be tapered to low levels or even discontinued. For those
patients who are not so fortunate, it is important to maintain control of the
hyperthyroidism throughout pregnancy to avoid severe thyrotoxicosis (thyroid
storm) developing during
labor and delivery. If this does develop, additional acute treatment with
beta-adrenergic blocking drugs are used.
If a woman has a severe negative reaction to anti-thyroid drugs, requires
very high doses to control her hyperthyroidism, or has uncontrolled
hyperthyroidism despite treatment, surgery may be recommended. The surgery would
usually be recommended during the second trimester, when it is least likely to
endanger the pregnancy.
In dealing with thyroid disease in pregnancy, the physician and patient
should be aware of problems that occur before and after, as well as during the
actual pregnancy. There should be equal concern for the welfare of both the
mother and baby. Fortunately, most thyroid conditions can be recognized,
problems can be anticipated, and effective treatment is available. The outcome
is almost always a healthy one, for both the mother and her baby.