Variations of urinary iodine during the first trimester of pregnancy in an iodine-replete area. Comparison with non-pregnant women

Objective: To assess variations of urinary iodine concentration (UIC) during a 4-week period among pregnant and non-pregnant women in an iodine-replete area. Design: Pregnant (in their first trimester of pregnancy) and non-pregnant women referred to two maternity hospitals in Tehran were consecutively recruited from September 2005 to March 2006. Urine samples (5-10 mL) were collected on an every-other-day basis for 4 weeks (i.e., 12 samples for each individual). UIC was determined using a modified Sandell-Kolthoff method. Results: Thirty-six pregnant and 32 non-pregnant women completed the study. Mean +/- SD age of pregnant women was 27.4 +/- 6.4 and of non-pregnant women 27.6 +/- 4.5 years (P = 0.897). Mean +/- SD gestational age was 11 +/- 3.3 weeks in pregnant participants. Median UIC of <100, 100-149, 150-249, and >= 250 mu g/L was present in 19.4, 25, 30.6, and 25% of pregnant, 15.6, 37.5, 34.4, and 12.5% of non-pregnant, and 17.6, 30.9, 32.4, and 19.1% of total individuals, respectively. Median UIC values of samples numbers 1 to 12 were not significantly different either in pregnant (P = 0.591) or in non-pregnant subjects (P = 0.745). Except for sample number 11, median UIC was not significantly different between pregnant versus non-pregnant women (P values >0.05). Mean SD values for UIC in samples numbers 1 to 12 in pregnant women was 138.4 (24.1-404) and in non-pregnant women 118 (29.5-272.4) mu g/L (P = 0.286). Conclusion: There was a wide intrapersonal variation in UIC values among pregnant and non-pregnant women residing in an iodine-replete area, supporting the notion that casual UIC would not reflect the iodine status of the individual.