Objective: To measure breast milk iodine (MI) and urinary iodine (UI) concentrations in healthy newborns and their nursing mothers from an iodine-sufficient region to determine adequacy and to relate these parameters to thyroid function tests in mothers and infants.
Design: Cross-sectional.
Patients: Forty-eight healthy neonates of 37 to 42 weeks' gestation with normal cord blood TSH values and their mothers were recruited in Tehran, Iran.
Measurements: Serum thyroid function tests were performed, and maternal and infant urinary iodine excretion, and maternal MI concentration were measured.
Results: Neonatal age was 12.9 +/- 3.9 (mean +/- SD; range 7-30) days and maternal age was 25.8 +/- 5 years. Median (range) UI in neonates was 271 microg/l (57-800) and in mothers was 107 microg/l (20-710). Median (range) MI was 148 microg/l (45-750). Neonatal and maternal UI did not correlate with serum thyroid function tests. UI < 150, 150-230, and > 230 microg/l was found in 20, 12.5, and 67.5% of neonates and 79.1, 14, and 7% of mothers, respectively. MI was < 150, 150-180, and > 180 microg/l in 52.4, 11.9, and 35.7% of mothers, respectively.
Conclusions: Among euthyroid neonates, UI was adequate despite low median maternal UI and MI concentrations. There were no significant correlations between UI or MI and thyroid function tests in the mothers and infants.