Babies Born to Mothers with Untreated Hypothyroidism Have
Lower I.Q.'s
Routine Thyroid Screening Should Occur
During Pregnancy
Dateline: 08/19/99
August 19, 1999 -- Today's New
England Journal of Medicine (NEJM) is reporting on the results
of a new research study that found that untreated hypothyroidism
during pregnancy may affect a child's psychological development, and
result in substantially lower I.Q. levels, reduced motor skills, and
problems with attention, language and reading.
The study found that women with untreated underactive thyroids
during pregnancy are nearly four times more likely to have children
with lower I.Q. scores. The researchers indicated that
approximately 1 out of every 50 women have hypothyroidism
(underactive thyroid) during pregnancy, however other experts
believe this number may actually be far larger, and that a larger
percentage of the population is undiagnosed
or undertreated.
The study showed that 19 percent of the children born to mothers
with thyroid deficiency had IQ scores of 85 or lower. This was
compared to a reduced IQ level of only 5 percent of those born to
mothers without such thyroid problems. According to James E. Haddow,
MD, lead study author, Vice President and Medical Director for the
Foundation for Blood Research, the range below 85 I.Q. level can
mean significant impairment for children.
"The children whose scores are in this range may face
life-long developmental challenges. It might be possible to
prevent these problems through the early diagnosis and treatment
of thyroid disease in their mothers."
The study found that the 62 children whose
mothers were hypothyroid during pregnancy performed less well on all
the various intelligence and IQ tests used for measurement. The
children of the 48 women who were not treated for thyroid disease
during the pregnancy had an average I.Q. score that was 7 points
lower than the children in the control group, with 19 percent
scoring 85 or less.
About Hypothyroidism and its Diagnosis
Hypothyroidism, the condition in which the thyroid is not
producing sufficient hormone, can result from thyroid surgery,
radioactive iodine ablation of a hyperactive thyroid, the presence
of thyroid nodules or goiter, or most commonly due to autoimmune
thyroid disease such as Hashimoto's. Common symptoms of
hypothyroidism include fatigue, weight gain, hair loss,
constipation, muscle weakness, slow heart rate, depression, dry
skin, and infertility, though dozens of symptoms are often seen in
hypothyroid patients. [See: Hypothyroidism
Symptoms Checklist" for a comprehensive list of symptoms.]
Many cases of hypothyroidism can be diagnosed via a standard test
known as the TSH test along with other key thyroid levels [Thyroid
Blood Test Levels Interpretation Chart] as well as via several
other methods, including the TRH
test, and antibodies testing..
Drug
treatment for hypothyroidism typically includes levothyroxine
(i.e., Levoxyl, Levothroid or Synthroid), an increasingly popular
combination of levoxyl with Cytomel, or thyroid hormone combination
drugs such as Thyrolar or Armour. The NEJM published in February of
1999 a research report that says that many patients feel better on a
combination drug versus the levothyroxine (i.e., Synthroid) alone.
[See
the NEJM article summary here.]
Interestingly, the researchers also found that the mothers who
were subsequently discovered to be hypothyroid had gone an average
of five years before their doctors diagnosed the thyroid disorder. A
few of the women were not diagnosed until 10 years later. This is an
ongoing problem for the entire population, and some estimates find
that there are as many as 13 million people with hypothyroidism in
the U.S., the majority of them women, and as many as half
undiagnosed. [See HELP!
My TSH Is "Normal" But I Think I'm Hypothyroid.]
Next Steps?
The NEJM mentioned that screening of pregnancy mothers for
hypothyroidism might be recommended. Typically, women who have
undergone a procedure to remove or ablate the thyroid, or who have a
diagnosed autoimmune hypothyroidism are aware of their
hypothyroidism, and should practice particular care in preparation
for pregnancy and in management of thyroid levels during pregnancy.
The greatest danger, however, is in the many women hypothyroidism
who are undiagnosed, who have normal thyroid levels with elevated
antibodies, or who have untreated subclinical hypothyroidism -- all
due to chronic autoimmune thyroiditis (Hashimoto's Thyroiditis).
The prevalence of this problem suggests that all women intending
to get pregnant should have a thyroid function test prior to
becoming pregnant, and during the early part of the first trimester,
and again in trimesters two and three, in order to ensure that
thyroid hormone levels are sufficient for both mother and fetal
health.
Another issue is concerns over iodine intake. In the New
England Journal editorial
accompanying the main
article, Dr. Robert D. Utiger says "Despite the presumption that
hypothyroidism in most pregnant women is caused by chronic
autoimmune thyroiditis, which cannot be prevented, the difference
among countries suggests another possible explanation -- iodine
deficiency, which is preventable. . . It is likely that both chronic
autoimmune thyroiditis and iodine deficiency contribute to the
occurrence of hypothyroidism in pregnant women in many countries."
This points to the key implication that prenatal vitamins should
ensure adequate iodine intake.
Before about 12 weeks' gestation, when a fetus' thyroid gland
becomes active, the mother is the sole source of thyroid hormones
for development of the fetus. Insufficient thyroid hormone in the
mother at that stage may be a particular danger to mother and baby,
and may in fact increase risk of miscarriage. This is why it is
particularly important for women with diagnosed thyroid disease to
work with a doctor who understands management of hypothyroidism,
particularly in the early stages and first trimester, when thyroid
hormone dosages sometimes need to be increased up to 40% in order to
meet the demands of pregnancy. In addition, there are some
particular theories regarding how high -- even within the normal
range -- it is safe for a hypothyroid mother to be, and these are
discussed in Thyroid
Disease and Pregnancy.
The Story
in The News
New England Journal
Articles
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successful pregnancy with hypothyroidism, alternative therapies for
hypothyroidism and its symptoms and side effects, combatting weight
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