Babies Born to Hypothyroid Mothers Have Lower I.Q.'s

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.