Urinary iodine excretion in pregnant women as an index of the impact of a national iodization programme

Abstract

Objective: To evaluate the extent to which increase in iodine requirement was achieved in pregnant women who attended the antenatal clinic at Harare Central Hospital. Design: Cross sectional. Setting: Samples were collected from pregnant women attending antenatal clinic at Harare Central Hospital, and from lactating mothers and their infants. Subjects: 100 pregnant women attending the antenatal clinic at Harare Central hospital, 80 infants, 80 lactating women and 18 non-pregnant women. Main Outcome Measures: Comparison of urinary iodine excretion levels among pregnant women, lactating mothers and their infants. Result: The results indicated lower urinary iodine excretion levels for the pregnant women and lactating mothers compared to the urinary iodine excretion of the infants and the breast milk iodine content. The urinary iodine excretion level of the non-pregnant control women was median (first and third quartiles): 18.5pg/dl (30.0, 30.2pg/dl). The urinary iodine excretion level of the lactating mothers was median (first and third quartiles): 12.0 mg/dl (7.6, 19.5 mg/dl) compared to the level of the infants, median (first and third quartiles): 26.5 mg/dl (18.8, 11.5 mg/dl). A significant difference was noted between the median urinary iodine excretion levels of the mothers, and the median levels of the infants, p = 0.001. The mean milk iodine content was 21.2 ± 6.8 mg/dl. There was no correlation between breast milk iodine levels and the urinary iodine excretion levels of the infants, (p = 0.96, r = 0.006). Positive correlation was found between maternal urinary iodine excretion levels and the urinary iodine excretion levels of the infants, p = 0.016 r = 0.285. Serum FT4, and TSH levels were found to be higher for infants at six weeks after birth, (FT4 =20.91± 65pmol,L) and median TSH= 2.28 mJU/ml (1.36, 0.86)mlU/rnl, compared to levels at 12 weeks postpartum: (FT4=17.53 -*6.4pmol/L) and median TSH=2.02 mlU/ml. (0.84. 1.55)mlU/ml. The differences were not significant. Conclusion: The results indicated a significant reduction in the urinary iodine content of pregnant women, and lactating mothers which did not appear to have any relationship to the urinary iodine excretion levels of infants and iodine content of breast milk. Iodine intake needed to be raised to reflect the recent proposed recommendation.