Relationship of Iodine Ingestion to Iodine Excretion in Pregnancy

An iodine balance study has been carried out on 5 pregnant and 2 nonpregnant women as well as 2 men, all euthyroid. For the studies, which were of 1–7 months' duration, all subjects were inpatients on a metabolic ward. Iodine measurements were obtained once a week for dietary intake and daily for urinary excretion; analyses of stool excretion were always on 6-day pooled samples. No significant difference in iodine balance was found between the pregnant and nonpregnant patients or between the antepartum or postpartum months in the pregnant patients. The usual method of calculating balances was of little use in interpreting balance data because of the fluctuations in dietary intake and therefore an additional method of data analysis was developed. With use of a 3-compartmen mathematical model of iodine metabolism, a linear relationship was predicted between the mean daily iodine balance and the iodine intake; this fits the observed data quite well and can be considered to be an iodine response curve. The slope and intercept of this line are indices of iodine metabolism which are functions of the turnover time of the body iodine pools and the mean dietary intake of iodine for the population. On the basis of our experiences, recommendations are made for the conduct of future balance studies with iodine and other elements.