The Comparison of Thyroid Function Tests in Cord Blood Following Cesarean Section or Vaginal Delivery

The present study was designed to assess the influence of mode of delivery on fetal pituitary-thyroid axis. The endocrine profile (umbilical venous plasma) of three groups of term infants was compared immediately after delivery. Samples were taken after 30 vaginal deliveries, 30 emergency cesarean sections during labor and 30 elective cesarean sections before labor. The study was performed in the Kowsar Hospital in Qazvin. The samples were matched based on maternal age, parity and gestational age and none of them had previous history of medical complications. Measurements of TSH and thyroid hormone levels were performed using immunoenzymometric and radioimmuno assays, respectively. Mean cord plasma TSH level of vaginal and emergency cesarean section was significantly lower than that of the elective cesarean section (p<0.0001; 3.3±1.8, 9.0±3.2 and 12.1±6.4 μU/mL, respectively). Mean concentrations of T4 and T3 were significantly higher in the elective cesarean section as compared with the emergencycesarean section and vaginal deliveries (p<0.05; 8.5±1.3, 7.4±2.4 and 7.4±1.3 μg/dL for T4 and 76±12, 62±20 and 51±16 ng/dL for T3, respectively). These results suggest that labor may reduce plasma thyrotropin and thyroid hormone concentrations at birth.