Influence of perinatal factors and sampling methods on TSH and thyroid hormone levels in cord blood.

To evaluate the effect of perinatal factors and sampling methods on thyroid stimulating hormone (TSH) and thyroid hormone levels in cord blood, serum TSH, free thyroxine (FT4) and free triiodothyronine (FT3) concentrations were measured in 124 healthy term neonates. Eighty-eight infants were born in normal vaginal deliveries, 25 were delivered by vacuum extractor and 11 by Cesarean section. There was no significant difference among the three infant groups in the mean TSH levels. Birth weight, the infant's sex, duration of labor and uterotonic agents had no effect on cord serum TSH and free thyroid hormone levels in the neonates born by normal vaginal delivery. To assess the adequacy of specimen collection, mixed cord blood samples, obtained by a direct application of cord on a filter paper, and venous blood withdrawn with a plastic syringe were collected in another 200 infants. There was a significant linear correlation in the TSH concentration in mixed cord blood and cord venous serum from the same individuals, while a poor correlation was found in T4 values from two specimens. Our results suggest that the TSH value in cord blood is less influenced by perinatal factors, including the sampling method, and the mixed cord blood collected by this technique might be a feasible alternative specimen for a TSH screening program with cord blood which is useful in countries where neonatal blood is not available.