The effect of type of delivery and povidone-iodine application at delivery on cord dried-blood-specimen thyrotropin level and the rate of hyperthyrotropinemia in mature and normal-birth-weight neonates residing in an iodine-replete area: report of Tehran Province, 1998-2005.

OBJECTIVE

To evaluate the effects of delivery type and of povidone-iodine disinfection at delivery on cord dried-blood-specimen (DBS) thyrotropin (TSH) concentrations.

METHODS

From 1998 to 2005, cord DBSs were collected from live deliveries in Tehran and Damavand, and TSH was assayed by a two-site immunoradiometric assay. Hyperthyrotropinemia was defined as TSH > or =20 mU/L. Vaginal deliveries prepared with povidone-iodine (VGL-PVP-I) or chlorhexidine (VGL-CHL), and cesarean sections prepared with povidone-iodine (CS-PVP-I) disinfection were assessed. Full-term, normal-size newborns were included. Iodine concentrations were measured in urine samples collected from 132 pregnant women immediately prior to delivery.

RESULTS

Median (range) TSH was 5.3 (1.0 to >100) mU/L in VGL-PVP-I (n = 23,432), 5.3 (1.0 to >100) mU/L in VGL-CHL (n = 5658), and 5.0 (1.0 to >100) mU/L in CS-PVP-I (n = 19,016) (p < 0.0001). Median TSH was higher in VGL-PVP-I versus CS-PVP-I (p < 0.0001) and in VGL-CHL versus CS-PVP-I (p < 0.0001). Hyperthyrotropinemia was present in 1.4%, 1.2%, and 0.8% of VGL-PVP-I, VGL-CHL, and CS-PVP-I deliveries, respectively, and was significantly higher in VGL-PVP-I versus CS-PVP-I (p < 0.0001) and in VGL-CHL versus CS-PVP-I (p = 0.005). Median (range) urinary iodine concentration of pregnant women was 176 (20-4600) microg/L.

CONCLUSION

Cord DBS TSH and rates of hyperthyrotropinemia are lower in cesarean section than in vaginal deliveries. Povidone-iodine disinfection at delivery has an effect neither on DBS TSH concentrations nor on the rate of hyperthyrotropinemia in the iodine-replete area of Iran.