Effect of perinatal factors on cord blood thyroid stimulating hormone levels

OBJECTIVE: To study the influence of perinatal factors on cord blood (CB) TSH levels. INFANTS AND METHODS: In a prospective cross-sectional study, CB TSH levels were measured in 1,590 live-born infants using IRMA. The effect of various perinatal factors on the CB TSH levels was analyzed statistically. RESULTS: The mean TSH level in the study group was 10.6 +/- 6.7 microU/ml (range 0.01-66.4 microU/ml). A significant fall in CB TSH levels was noted with increasing gestational age. A similar decline was noted in TSH levels with increase in birth weight. No significant difference in TSH levels was noted between males and females, or AGA and SGA (n = 296) infants. Infants with birth asphyxia (Apgar score < 4 at 5 min) had significantly higher CB TSH levels (mean 31 microU/ml, n = 18) as compared to those without (mean 10.4 microU/ml) (p < 0.01). The highest TSH levels were noted in neonates delivered by forceps extraction (mean 29.4 microU/ml, n = 17) and lowest levels in infants born by elective Caesarian section (mean 8.7 microU/ml, n = 149). CONCLUSION: CB TSH levels fall with increase in gestational age while birth asphyxia and difficult deliveries tend to elevate them.