Context The developing thyroid is sensitive to iodine overload with exposure potentially resulting in goitre and/or hypothyroidism. The British National Formulary (BNF) lists neonates <32 weeks gestation and infants under 1.5 Kg as contra-indications for the use of povidone-iodine for skin disinfection, and recommends its avoidance during pregnancy and breast feeding. The BNF makes no recommendation on the use of iodinated-contrast media, as it is not a listed drug. Existing research in this area is inconsistent and based on small, outdated studies.

Aim Are neonatal thyroid hormone levels in preterm infants changed by maternal, fetal or neonatal exposure to iodine?

Methods Case-comparison study of infants born <32 weeks gestation.

Main outcomes Levels of thyroxine, thyroxine binding globulin and thyroid stimulating hormone (TSH) measured on Guthrie card on postnatal day 7, 14 and 28 and at 36 corrected weeks gestation.

Results 125 infants were potentially exposed and 48 infants not exposed to iodine from contrast media and/or povidone-iodine during labour. 13 infants recorded a TSH ≥6 mU/L in the first 28 days postnatal: 6% of infants were exposed to contrast media, 15% were exposed to povidone-iodine during labour, and 8% had no known exposure. No infants were diagnosed with transient hypothyroidism, 3 infants (exposed to contrast media) had transient hyperthyrotropinaemia (10–19 mU/L).

Comment In the context of this small pilot study, the incidence of raised TSH levels appears higher in infants exposed to iodine during labour but not in those exposed to contrast media. A large study is now planned.