Background: Since the initiation of neonatal screening-programs for congenital hypothyroidism (CH) in the 1970s, an increase in the incidence of CH has been observed. This change has been attributed to the gradual use of lower TSH cut-offs that lead to the detection of milder cases of CH. Based on currently used screening cut-offs, CH occurs in approximately 1:2 000 to 1:4 000 newborns, varying by geographic location and ethnicity. A female predominance, approaching a 2:1 female to male ratio, has been consistently reported.
Objective and hypotheses: To assess whether the gradual decrease in the TSH cut-off limits has affected the female to male ratio in neonates with CH.
Method: The yearly records from 1980 to 2014 of the Greek National Neonatal CH screening program were thoroughly reviewed. For each year, the TSH cut-off point was noted and the percentage of female neonates diagnosed with CH was calculated.
Results: The National Greek Neonatal CH screening program was initiated in 1980. Over the following 35 years, more than 3 690 000 neonates were screened. The TSH cut-off point was gradually lowered from 30 mIU/ml in 1980 to 6 mIU/ml in 2006 and moved back to 8 mIU/ml as of 2012. The proportion of female neonates diagnosed with CH was 78% in 1980 but showed a progressive decrease to lower than 50% in the last decade. In fact, the use of a 68 mIU/ml TSH cut-off point led to marginal male predominance.
Conclusion: Change of the TSH cut-off point used in the CH screening program alters the female to male ratio. Specifically, lowering the TSH limit results in a decrease of female percentage among neonates with CH. When a 68 mIU/ml TSH cut-off point is applied, an inversion of the female to male ratio is observed and male preponderance is noted.
01 - 03 Oct 2015
European Society for Paediatric Endocrinology