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Iodine and the Body

Pregnancy

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Haddow

Urine Iodine Measurements, Creatinine Adjustment and Thyroid Deficiency in an Adult United States Population.

Haddow JE, McClain MR, Palomaki GE, Hollowell JG.

J Clin Endocrinol Metab. 2007 Jan 2

"Purpose: To explore the relationships between urine iodine, creatinine, serum TSH and total T4 in a diverse population of United States adults with the aim of determining whether low urine iodine is associated with thyroid deficiency.

Methods: Using the NHANES III data set, we examined median TSH and total T4 values according to deciles of urine iodine (with and without creatinine correction). Stepwise regression analysis was used to further explore these relationships in the context of possible confounding variables. Exclusion criteria included age less than 21 years, pregnancy and the presence of thyroid antibodies.

Results: Among the 5,963 men and 5,722 women, median urine iodine concentrations do not vary with increasing age, while median creatinine levels decrease (p<0.001). Urine iodine and creatinine concentrations are lower among women (p<0.001). TSH increases with age (p<0.001), while total T4 decreases (p<0.001). Neither TSH nor total T4 median values are associated with urine iodine. If the urine iodine to creatinine ratio is used instead, an extensive re-distribution of study subjects occurs that results in an apparent positive relationship between this ratio and TSH measurements. A multivariate regression analysis that accounts for age, BMI, race, creatinine, iodine, estrogen use, smoking, and gender reveals only a weak association between levels of urine iodine and markers of thyroid function.

Conclusions: Our analyses indicate that the United States non-pregnant, adult population is iodine sufficient."

Maternal thyroid deficiency during pregnancy and subsequent neuropsychological development of the child.

Haddow JE, Palomaki GE, Allan WC, Williams JR, Knight GJ, Gagnon J, O'Heir CE, Mitchell ML, Hermos RJ, Waisbren SE, Faix JD, Klein RZ.

N Engl J Med. 1999 Aug 19;341(8):549-55.
 

"BACKGROUND: When thyroid deficiency occurs simultaneously in a pregnant woman and her fetus, the child's neuropsychological development is adversely affected. Whether developmental problems occur when only the mother has hypothyroidism during pregnancy is not known.

METHODS: In 1996 and 1997, we measured thyrotropin in stored serum samples collected from 25,216 pregnant women between January 1987 and March 1990. We then located 47 women with serum thyrotropin concentrations at or above the 99.7th percentile of the values for all the pregnant women, 15 women with values between the 98th and 99.6th percentiles, inclusive, in combination with low thyroxine levels, and 124 matched women with normal values. Their seven-to-nine-year-old children, none of whom had hypothyroidism as newborns, underwent 15 tests relating to intelligence, attention, language, reading ability, school performance, and visual-motor performance.

RESULTS: The children of the 62 women with high serum thyrotropin concentrations performed slightly less well on all 15 tests. Their full-scale IQ scores on the Wechsler Intelligence Scale for Children, third edition, averaged 4 points lower than those of the children of the 124 matched control women (P= 0.06); 15 percent had scores of 85 or less, as compared with 5 percent of the matched control children. Of the 62 women with thyroid deficiency, 48 were not treated for the condition during the pregnancy under study. The full-scale IQ scores of their children averaged 7 points lower than those of the 124 matched control children (P=0.005); 19 percent had scores of 85 or less. Eleven years after the pregnancy under study, 64 percent of the untreated women and 4 percent of the matched control women had confirmed hypothyroidism.

CONCLUSIONS: Undiagnosed hypothyroidism in pregnant women may adversely affect their fetuses; therefore, screening for thyroid deficiency during pregnancy may be warranted."

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