Maternal Thyroid Function, Iodine Deficiency and Fetal Development

Abstract

In an area of New Guinea where there is dietary iodine deficiency, measurements of thyroid function have been made on women of child-bearing age, several of whom were pregnant at the time. The outcome of these pregnancies, and also of those occurring in the four preceding years, were examined in relation to indices of thyroid function. More stillbirths, infant deaths and endemic cretins occurred among the offspring of women who showed biochemical evidence of iodine deficiency, without clinical evidence of hypothyroidism. This situation differs from that of untreated myxoedema or congenital hypothyroidism in women, which is usually associated with altered menstrual function, infertility or repeated abortion. Mechanisms that may account for these differences and the possible implications are discussed.

Iodine deficiency and brain development in the first half of pregnancy

“…It was also shown that to prevent the birth of cretins, interventions that corrected the ID (and the maternal hypothyroxinemia) were required very early in pregnancy and before mid-gestation at the latest 12,15,16 . Since these studies, evidence has accumulated showing that treatment early in pregnancy is required not only to prevent cretinism, but also to avoid the lowered intelligence quotient suffered by the rest of the inhabitants of such areas 17 -21 .…”

“…A series of studies in Papua New Guinea 11,12 and in Andean regions where endemic goitre with cretinism occurs 13,14 , showed that pregnant women in such places were unable to respond to the onset of pregnancy with an increase in circulating thyroxine (measured then by serum protein-bound iodine), which is the normal physiological response to the onset of pregnancy in women with an adequate iodine intake. It was also shown that to prevent the birth of cretins, interventions that corrected the ID (and the maternal hypothyroxinemia) were required very early in pregnancy and before mid-gestation at the latest 12,15,16 .…”

Correlation Between Thyroid Dysfunction and Infertility

“…33 Estimation of serum TSH proves to be the most sensitive index of thyroid failure. 34,35 TSH possess a luteotropic activity and reach one fifth of the biological activity of hCG. TRH or T3 or T4 do not possess luteotropic activity.…”

Understanding Prenatal Iodine Deficiency

“…However, the prenatal origin of this syndrome was confirmed when a clinical trial with iodized oil showed that it could be successfully prevented exclusively when iodine was supplied to the mother before conception. 3 The classic works by Pharoah et al 3,27 in Papua New Guinea in the 70's, and later by Thilly et al 4 in Ubangi (Zaire) and Malawi, provided a thorough description of the clinical symptoms of endemic cretinism (in its myxedema and neurological forms), which were characteristic of regions with severe endemic goiter.…”

“…Cases of intrauterine deaths, miscarriages, death in childhood and the birth of cretins to women with biochemical evidence of iodine deficiency (very low free T4 levels) without clinical signs of hypothyroidism were described. 28,29 In 1976, Pharoah et al 27 pointed out that iodine deficiency was different from untreated myxedema and from congenital hypothyroidism, which are usually associated with menstrual disorders, infertility or repeated miscarriage.…”