Objectives: To determine the prevalence of congenital hypothyroidism, establish reference levels for thyroid stimulating hormone (TSH), and determine the cut-off points of TSH level for neonatal screening in congenital hypothyroidism.
Design: A cross-sectional study.
Setting: Ghandhi Memorial, Zewditu, Tikur Anbessa and St Paulo's referral hospitals in Addis Ababa, Ethiopia, from July 1996 to January 1997.
Subjects: Four thousand two hundred and six consecutive newborns.
Main outcome measures: TSH and T4 values using standard TSH level estimation approach.
Results: The overall mean TSH value was 9.6 mIU/l with standard deviation of 7.8 mIU/l. Transient hypothyroidism occurred in 3.6% of the neonates. No true case of congenital hypothyroidism was identified. The mean(SD) sampling time was 12.8(6.7) hours and the recall rate 4.8%. Most neonates (98.6%) were screened at or less than 24 hours of age. Twins had lower mean TSH value of 7.9(SD=6.4) mIU/l than single neonates with 9.6(SD=7.8) mIU/l, while females had significantly lower mean TSH value of 9.4(SD=7.9) mIU/l than males of 9.8(SD=7.6) mIU/l. The mean TSH level decreased significantly as sampling time increases, the mean TSH level for neonates older than 24 hours is significantly lower than the mean TSH level for those with 24 hours old or less. No significant difference was found in the mean TSH levels in relation to maternal age, parity and gestational age. No significant correlation was found between TSH value and birth weight (r=0.02), height (r=0.03), and head circumference (r=0.02) of the neonates. The most appropriate TSH level cut-off point was found to be at 29.4 mIU/l. The reference range (the range between 2.5th and 97.5th percentiles) for serum thyrotrophin value was higher in the age range of 6 to 12 hours and then declined.
Conclusion: This pilot study has highlighted important findings, however larger studies should be conducted to assess the magnitude and associated factors of congenital hypothyroidism because congenital hypothyroidism represents one of the most common preventable causes of mental retardation.