Congenital Hypothyroidism in Newborns: Prevalence and Clinical Significance
Congenital hypothyroidism is relatively common, affecting approximately 1 in 2,000 to 4,000 newborns, making it one of the most frequent preventable causes of intellectual disability. 1, 2, 3
Epidemiologic Data
The prevalence of congenital hypothyroidism varies slightly across different populations and screening programs:
- Standard prevalence: 1:2,000 to 1:4,000 live births is consistently reported across multiple studies 1, 2, 3
- Regional variation: In southeastern Poland, screening of 233,120 neonates revealed permanent congenital hypothyroidism in 1:6,475 births, with transient forms occurring in 1:38,853 4
- Ireland's experience: Among 2,361,174 infants screened over 37 years, 1,063 babies were diagnosed and treated, confirming the condition's relatively common occurrence 5
Clinical Importance and Screening Rationale
Congenital hypothyroidism ranks among the highest priority conditions for newborn screening, scoring alongside phenylketonuria (PKU) and MCAD deficiency in systematic evaluations of screening programs. 6
The condition warrants universal screening because:
- Newborn screening is offered throughout the United States and should be performed in all infants 7
- Clinical manifestations are often subtle or absent at birth due to transplacental passage of maternal thyroid hormone 1
- Treatment in the first several weeks of life can result in nearly normal intelligence and growth 7
- Without treatment, severe intellectual deficit and short stature are inevitable 3
Common Clinical Presentations
When symptoms do appear, they typically include:
- Decreased activity and increased sleep 1, 3
- Feeding difficulty and constipation 1, 3
- Prolonged jaundice 1, 2
- Myxedematous facies, large fontanels (especially posterior), and macroglossia 1, 2, 3
- Distended abdomen with umbilical hernia and hypotonia 1, 2, 3
Critical Screening Considerations
A significant proportion of infants with borderline TSH elevations (8-10 mU/L on whole-blood screening) have permanent, decompensated hypothyroidism, challenging the use of higher screening thresholds 5. Among 33 infants with screening TSH between 8-9.9 mU/L, 13 had decompensated hypothyroidism with low free T4, and 41% had confirmed permanent disease 5.