ATA Guidelines Tools

5 Î The accuracy of serum Free T4 measurement by the indirect analog immunoassays is influenced by pregnancy and also varies significantly by manufacturer. If measured in pregnant women, assay method- specific and trimester-specific pregnancy reference ranges should be applied. (S-M) Î In lieu of measuring free T4, total T4 measurement (with a pregnancy- adjusted reference range), is a highly reliable means of estimating hormone concentration during the last part of pregnancy. Accurate estimation of the free T4 concentrations can also be done by calculating a free thyroxine index. (S-M) • A total T4 upper range determination can be calculated by shifting the nonpregnant limit 50% higher. However, this can only be used after week 16 of pregnancy. If a T4 measurement is required before that time (i.e. weeks 7–16 of pregnancy), a calculation can be made for the upper reference range based on increasing the non-pregnant upper reference limit by 5% per week, beginning with week 7. For example, at 11 weeks of gestation (4 weeks beyond week 7), the upper reference range for T4 is increased by 20% (four weeks × 5%/week) Iodine Status and Nutrition Î Median urinary iodine concentrations can be used to assess the iodine status of populations, but single spot or 24-hour urine iodine concentrations are NOT valid markers for the iodine nutritional status of individual patients. (S-H) Î All pregnant women should ingest approximately 250 μg iodine daily. To achieve a total of 250 μg iodine ingestion daily, strategies may need to be varied based on country of origin. (S-H) Î In most regions, including the United States, women who are planning pregnancy or currently pregnant should supplement their diet with a daily oral supplement that contains 150 μg of iodine in the form of potassium iodide. This is optimally started 3 months in advance of planned pregnancy. (S-M) Î In low-resource countries and regions where neither salt iodization nor daily iodine supplements are feasible, a single annual dose of ~400 mg iodized oil for pregnant women and women of childbearing age can be used as a temporary measure to protect vulnerable populations. This should NOT be employed as a long-term strategy or in regions where other options are available. (W-M). Î There is no need to initiate iodine supplementation in pregnant women who are being treated for hyperthyroidism or who are taking levothyroxine (LT4). (W-L)

• Cover