The increased incidence of congenital hypothyroidism: fact or fancy?

Marvin L. Mitchell, University of Massachusetts Medical School
Ho-Wen Hsu, University of Massachusetts Medical School
Inderneel Sahai, University of Massachusetts Medical School
Stuart J. Brink, Tufts University
Laurie E. Cohen, Harvard Medical School
Rosalind S. Brown, University of Massachusetts Medical School
Roger B. Eaton, University of Massachusetts Medical School
Mary M. Lee, University of Massachusetts Medical School
Lynne L. Levitsky, Harvard Medical School
Edward Reiter
Abdollah Sadeghi-Nejad, Tufts University
Leslie A. Soyka, University of Massachusetts Medical School
Joseph I. Wolfsdorf, Harvard Medical School
Massachusetts Pediatric Endocrine Work Group

Abstract

OBJECTIVE: The incidence of congenital hypothyroidism (CH) detected by newborn screening in the US has increased significantly since the early 1990s. We defined the characteristics associated with the increased incidence.

PATIENTS: A cohort of children with CH born during an earlier period of low incidence (1991-94) was compared with a cohort born during a later period when the incidence of CH had doubled (2001-04).

MEASUREMENTS: Screening was performed with T4 as the primary marker and thyroid stimulating hormone (TSH) on selected specimens. Follow-up on hypothyroid children determined whether they had permanent or transient hypothyroidism. Cases were classified based on laboratory results: initial TSH ≥100 mU/l was 'severe,' initial TSH/l but ≥20 mU/l was 'mild' and initial TSH/l with subsequent abnormal TSH was 'delayed'.

RESULTS: The overall incidence of CH almost doubled between the two time periods, from 1:3010 to 1:1660. Excess cases were found in the mild and delayed categories, with no increase in severe cases. The proportion of transient cases was

CONCLUSION: The rising incidence of CH in Massachusetts is confined to mild and delayed cases. Our findings suggest that this rise is attributable to enhanced detection rather than an absolute increase in numbers.