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| FOR IMMEDIATE RELEASE Sept. 18, 2003, 9:45 a.m. EDT |
For more information, please contact the ATA at thyroid@thyroid.org. |
Women With Thyroid Hormone Deficiency Who Become Pregnant Need Immediate Evaluation, Can Protect Fetal Brain Development
(PALM BEACH, FLA., Sept. 18, 2003) - Women with a deficiency of thyroid
hormone should have their hormone levels checked as soon as pregnancy
is confirmed and begin treatment immediately if hormone levels are low,
according to a study reported today at the 75th Annual Meeting of the
American Thyroid Association. Currently, there is no standard protocol
for evaluation of hypothyroid women who become pregnant because the precise
timing of the increase in thyroid hormone has not been known.
"It has been estimated that 1 percent to 2 percent of all pregnant
women receive drug therapy for hypothyroidism prenatally and would be
affected by these findings," said P. Reed Larsen, MD, senior author
of the study and professor of medicine at Harvard Medical School and chief,
Division of Endocrinology, Diabetes and Hypertension at Brigham and Women's
Hospital in Boston. "Given the nearly 4 million live births that
occur annually in the United States, prenatal care may be affected in
40,000-80,000 pregnant women."
Hypothyroidism is a deficiency in the thyroid that plays a critical role
in regulating important functions in the body, such as heart rate, metabolism,
growth, cognitive function and development, energy, and mood. Treatment
of the disorder is medication, most commonly a drug called levothyroxine,
to replace the deficient thyroid hormone.
In all women, pregnancy increases the demands on the thyroid, which produces
the thyroid hormone needed by the fetus for proper fetal development.
In most women, this extra load on the thyroid is not problematic. However,
for hypothyroid women, pregnancy causes a rapid and early increase in
the dose of thyroid hormone needed to maintain a normal level. Previous
studies have suggested that maternal hypothyroidism may affect future
cognitive development, seen later in lower IQ scores, in the unborn infant.
Although not common, if the hypothyroidism becomes severe, miscarriage
is a possibility. Approximately one out of every 50 women in the United
States is thyroid deficient during pregnancy.
"Our study provides the first prospective evaluation
of this issue," said Erik K. Alexander, MD, lead author of the study
and associate physician at Brigham and Women's Hospital. "Most often,
a routine thyroid blood test is performed sometime during the first trimester;
and if at that time hormone levels are found to be abnormal, the dose
of hormone will be increased."
To better identify when a pregnant women with hypothyroidism needs to
be evaluated, Dr. Alexander and colleagues studied 21 women with hypothyroidism
who were planning a pregnancy. The women were classified as being hypothyroid
due either to thyroidectomy and/or radioactive iodine therapy to treat
an overactive gland or thyroid cancer (12) or Hashimoto's disease (9),
three of whom were undergoing assisted reproduction (AR). Thyroid function
was measured before conception, every two weeks during the first trimester,
and monthly thereafter. Thyroid hormone dose was adjusted to maintain
the hormone concentrations at pre-conception levels.
Nineteen women became pregnant and, of those, 16 infants were delivered
at term. At the time of the first test (on average at five weeks), 53
percent had an increase in thyroid-stimulating hormone (TSH), which stimulates
the thyroid gland to secrete hormones. Greater than normal levels indicate
hypothyroidism. TSH increased earlier and to a greater degree in those
who conceived with AR. For women whose thyroid had been surgically removed
or destroyed with the use of radioactive iodine, the average TH requirement
increased 49 percent during gestation, beginning as early as week three
and plateauing after week 16. The most rapid increase in the dose of thyroid
hormone required occurred between weeks eight and 16, coinciding with
the peak of maternal hCG, a hormone secreted early in pregnancy. The researchers
state that hypothyroid women should increase thyroid hormone intake by
50 percent as soon as pregnancy is confirmed and monitor TSH monthly until
stabilization.
"This increased requirement appears related to changes in estradiol
concentrations and persists throughout all of pregnancy," added Dr.
Alexander. "Because of possible harmful consequences to both the
mother and fetus of allowing thyroid hormone levels to become low, such
women are advised to notify their physician as soon as pregnancy is confirmed."
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