Postpartum maternal iodine status and the relationship to neonatal thyroid function.
Iodine deficiency in the postpartum period has the potential to affect neonatal neuropsychointellectual development. We performed a cross-sectional study involving 50 postpartum women and their neonates, measuring maternal urine iodine, breast milk iodine, and neonatal thyroid stimulating hormone (TSH), and examining their interrelationships. Women were studied at a median (range) of 4 (3-9) days postpartum. Moderate to severe iodine deficiency (defined by urine iodine concentration < 50 microg/L) was found in 29 of the 50 subjects (58%). The median +/- standard deviation (SD) urine iodine was 46.8 +/- 28.5 microg/L and the mean urine iodine expressed in micrograms per gram of creatinine was 86.6 +/- 45.6. The median (range) breast milk iodine was 84.0 microg/L (25.0-234.0). Breast milk iodine was significantly correlated with urine iodine in micrograms per gram of creatinine (r = 0.52, p < 0.001) but not with urine iodine measured in micrograms per liter (r = 0.19, p = 0.2). Six percent of neonates had whole-blood TSH values of greater than 5 mIU/L. Neonatal TSH levels were positively correlated with higher breast milk iodine (r = 0.42, p = 0.003). There was no significant correlation between neonatal TSH levels and the mother's urine iodine content. There is a high prevalence of iodine deficiency in these lactating postpartum subjects. Urine iodine as micrograms per gram of creatinine is a good predictor of breast milk iodine content. In our study, higher breast milk iodine was correlated with a higher neonatal TSH. The impact of breast milk iodine content on neonatal TSH levels and neuropsychointellectual development needs further study.
Department of Endocrinology, Royal North Shore Hospital, St Leonards, Australia. ssychan@med.usyd.edu.au
Sophie S Y
SS
Chan
Graham
G
Hams
Veronica
V
Wiley
Bridget
B
Wilcken
Aidan
A
McElduff
D000328:Adult; D002585:Cesarean Section; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007231:Infant, Newborn / Q000097:blood / Q000502:physiology*; D007455:Iodine / Q000032:analysis* / Q000172:deficiency / Q000652:urine; D008895:Milk, Human / Q000737:chemistry; D009321:Natural Childbirth; D049590:Postpartum Period / Q000378:metabolism*; D012044:Regression Analysis; D013961:Thyroid Gland / Q000502:physiology*; D013972:Thyrotropin / Q000097:blood
D013972:Thyrotropin; D007455:Iodine