| Maternal
Thyroid Deficiency During Pregnancy In the first trimester (3 mos) of pregnancy, the fetus is completely dependent upon the mother for thyroid hormone. During the second and final trimesters of pregnancy, most fetuses are able to provide some thyroid hormone but also continue to rely upon their mothers for some hormone. Problems of brain development occur when either the mother is unable to provide for the fetus’ needs in the first trimester, or neither the mother nor the fetus can provide for fetal needs during the remainder of pregnancy. Another important issue is the availability of iodine to the mother since idodine is an important requirement to provide for proper thyroid production by both the mother and the developing fetus. Should all pregnant women routinely be evaluated for thyroid function early in pregnancy? The thyroid status of a large group of pregnant women and their offsprings were evaluated by the authors.1 In those women with low levels of thyroid hormone, the authors show that hypothyroidism (low thyroid function) adversely affects the child’s performance on tests of intelligence, language, reading ability and motor performance. This can be true even when the mother is presenting no symptoms. As a result of their study, the authors suggest that an evaluation of the mother’s thyroid function should become routine early in pregnancy for all women. In an editorial in the same journal (pages 601-602), Dr. Robert D. Utiger raises questions about the cost/benefit effects of routine examination of thyroid function in all pregnant women. He suggests instead that since iodine is essential for thyroid hormone production, and adequate supply of iodine needs to be made available to all pregnant women. This is particularly true in that a common source of iodine in the U.S. diet is iodized table salt. With efforts to decrease the use of table salt in order to prevent high blood pressure, the consumption of iodine may no longer be adequate—particularly for pregnant women. He suggests iodine needs to be added to other foods and be included in all vitamin products as the fist step to prevent developmental brain damage due to maternal hypothyroidism. Thus, he proposes that before a national program of routine thyroid function in pregnant women is initiated and increased supply of iodine be added to vitamin products used by pregnant women. Comment: It has been recognized for a very long time
that an adequate supply of thyroid hormone is essential for normal brain
development. This is true during the entire period of pregnancy but it
particularly true in the last half of pregnancy and in the early years
of infant life. Modest thyroid hormone insufficiency leads to cognitive
inadequacies (e.g. learning disabilities); a large insufficiency leads
also to neurological deficits—spasticity, poor balance and deafness.
In women at risk of a troubled pregnancy, a thorough thyroid function
evaluation early in pregnancy would certainly seem prudent. Also, an available
source of iodine within the diet or by dietary supplements (e.g. iodine
fortified vitamins) should be routine. In addition, attention needs to
be given to the thyroid hormone status so the newborn infant; and in selected
cases to the infant several weeks after birth to make certain the infant’s
thyroid gland continues to function properly.
There are no longer any questions about the absolute requirement of thyroid
hormone for adequate brain development. Both pregnant women and their
physicians need to recognize this on the “check list” of things
to consider to foster normal development of the developing brain. |