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.
Chan
Sophie S Y
SS
Department of Endocrinology, Royal North Shore Hospital, St Leonards, Australia. ssychan@med.usyd.edu.au
Hams
Graham
G
Wiley
Veronica
V
Wilcken
Bridget
B
McElduff
Aidan
A
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