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to add 120 to 180 μg/day of iodine (Romano et al., 1991). Their urinary iodine increased from 37 to 154 μg/day during the second trimester and was 100 μg/day during the third trimester. Untreated control subjects showed little change. The initial thyroid volume of 9.8 mL did not change in those treated with iodine, but increased by 16 percent in the controls. Thus, the total daily iodine intake of about 200 μg prevented goiter. In another study from Denmark (Pedersen et al., 1993), 54 pregnant women were given 200 μg/day of iodine as potassium iodide drops beginning the second trimester. Urinary iodine increased from 55 to 105 μg/L, their thyroid volume (initially 9.6 mL) increased by 15.5 percent, and serum thyroid stimulating hormone (TSH) and serum thyroglobulin (Tg) concentrations did not change. Untreated control subjects showed increases of 31 percent in thyroid volume, 75 percent in serum Tg concentration, and 21 percent in serum TSH concentration. Thus, approximately 250 to 280 μg/day of iodine prevented goiter during pregnancy. In a third study (Glinoer, 1998), pregnant women with an initial urinary iodine of 36 μg/L were treated with an additional 100 μg/day. Their median urinary iodine concentration increased to 100 μg/L at 33 weeks, and their thyroid volume increased by 15 percent, compared with 30 percent in control subjects. Thus, a supplement of 100 μg iodine, bringing the total daily iodine intake to about 150 μg/day, was insufficient to prevent increased thyroid size.

On the basis of the above data, the EAR is set at 160 μg/day.

Iodine EAR and RDA Summary, Pregnancy

EAR for Pregnancy

 

14–18 years

160 μg/day of iodine

19–30 years

160 μg/day of iodine

31–50 years

160 μg/day of iodine

The RDA for iodine is set by using a CV of 20 percent (see “Adults Ages 19 Years and Older”). The RDA is defined as equal to the EAR plus twice the CV to cover the needs of 97 to 98 percent of individuals in the group (therefore, for iodine the RDA is 140 percent of the EAR). The calculated values for RDAs were rounded to the nearest 10 μg.

RDA for Pregnancy

 

14–18 years

220 μg/day of iodine

19–30 years

220 μg/day of iodine

31–50 years

220 μg/day of iodine



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