The Potential Repercussions of Maternal, Fetal, and Neonatal Hypothyroxinemia on the Progeny

Abstract

The adequate functioning of both the maternal and fetal thyroid glands play an important role to ensure that the fetal neuropsycho-intellectual development progresses normally. Three sets of clinical disorders are considered, that may eventually lead to impaired brain development. Firstly, in infants with a defect of glandular ontogenesis (congenital hypothyroidism), the participation of maternal thyroid hormones to the fetal circulating thyroxine environment is normal and, therefore, risk of brain damage results exclusively from the insufficient hormone production by the abnormal fetal thyroid gland. Secondly, when it is only the maternal thyroid gland that is functionally deficient (autoimmune hypothyroidism), the severity and temporal occurrence of maternal underfunction will both drive the resulting consequences for impaired fetal neuronal development. Clinical situations of this type may obviously take place already during early gestation (in women with known but untreated hypothyroidism) or appear only during later gestational stages (in women who have AITD and remain euthyroid during the first half of gestation). Lastly, in conditions with iodine deficiency, both maternal and fetal thyroid functions are affected and, therefore, it is primarily the degree and precocity of the maternal hypothyroxinemia due to iodine deficiency during pregnancy that will drive the potential repercussions for fetal neurological development. In the present review, we summarize available data and develop our present concepts concerning the complex feto-maternal thyroid relationships and the potential impacts of thyroid function abnormalities on the ideal development of the offspring.

Iodine deficiency in pregnant women in eastern Turkey (Malatya Province): 7 years after the introduction of mandatory table salt iodization

“…Even mild or subclinical hypothyroidism during pregnancy may affect the mental development of the infant (2,18) . For this reason, an adequate dietary intake of I throughout the pregnancy period is highly important.…”

Seasonality in urinary and household salt iodine content among pregnant and lactating women of the plains of Nepal

“…Pregnancy and lactation create different demands on the individual for iodine, and an understanding of iodine metabolism across reproduction may help to explain the persistent difference in iodine status between pregnant and lactating women in this study. Iodine is required for the increased production of maternal thyroxine throughout pregnancy and for fetal thyroid hormone production after the second trimester (Delange et al, 1988;Glinoer & Delange, 2000). However, in addition to the enhanced demand for iodine, renal clearance of iodine increases during pregnancy (Aboul-Khair et al, 1964), resulting in increased urinary losses of iodine compared to the nonpregnant state.…”

“…Transient hypothyroidism and increased thyroid volume have been observed in women and in neonates of women with mild-tomoderate iodine deficiency during pregnancy (Pedersen et al, 1993;Glinoer et al, 1995;Kung et al, 1997). Studies suggest that cognitive impairment may exist among children whose mothers were even mildly iodine deficient during pregnancy (Glinoer & Delange, 2000). Iodine is also required for the continued postnatal brain development of the young infant (Delange et al, 1988;Glinoer & Delange, 2000), and in countries where exclusive breast-feeding is practiced, breastmilk is likely to be an essential source of dietary iodine for the young infant.…”

“…Studies suggest that cognitive impairment may exist among children whose mothers were even mildly iodine deficient during pregnancy (Glinoer & Delange, 2000). Iodine is also required for the continued postnatal brain development of the young infant (Delange et al, 1988;Glinoer & Delange, 2000), and in countries where exclusive breast-feeding is practiced, breastmilk is likely to be an essential source of dietary iodine for the young infant. Thus, pregnancy and lactation represent high-risk periods for monitoring prevalence of iodine deficiency and evaluating the impact of programs to control it when dietary iodine is likely to be lacking.…”

Iodine supplementation of pregnant women in Europe: a review and recommendations

“…The fetal brain is particularly vulnerable to maternal hypothyroidism in iodine deficiency, and iodine deficiency is the leading cause worldwide of preventable mental retardation (Bleichrodt & Born, 1994). Even mild or subclinical maternal hypothyroidism during pregnancy can impair mental development of the newborn (Haddow et al, 1999;Glinoer & Delange, 2000). This paper discusses: (a) the iodine nutrition of pregnant women and women of child-bearing age in Europe; (b) the use of iodine-containing supplements by these groups; (c) trials of iodine supplementation in pregnancy; and (d) the availability and regulation of iodine-containing supplements in Europe.…”