Table 1.

Summary of key studies evaluating the epidemiology of CH over time.

Reference	Time period	Country	CH incidence	TCH incidence	Likely causes
Chiesa et al. (13)	1997–2010	Argentina	GIS CH increased in incidence	No significant change	Change in TSH cut points. (partly). Possible contribution of iodine deficiency
Kara et al (7)	2008–2010	Turkey	Two-fold increase in PCH, five-fold increase in TCH since past evaluations with higher TSH cut point (20 mU/L)	52% cases had TCH. TCH increased from 35% (2008) to 56% (2009–2010) when TSH cut point further decreased	Increased incidence of PCH and TCH partly due to decreased TSH cut points; High overall incidence of TCH possibly due to I- deficiency
Mitrovic et al. (6)	1983–2013	Serbia	Overall CH incidence tripled as TSH cut point decreased. PCH due to ectopy/GIS/goitre doubled, athyreosis stable.	TCH increased from 0 to 35%	Decreased TSH cutoffs; Other yet unidentified factors.
Mitchell et al. (9)	1991–1994; 2001–2004	USA	CH incidence doubled due to increased cases with delayed or mild TSH elevation. Severe CH stable.	TCH stable	Mainly due to enhanced detection of infants with mild disease and premature infants with delayed TSH rise due to altered screening strategy
McGrath et al. (14)	1979–2016	Ireland	Increased incidence of CH from 0.27 (1979–1991) to 0.65 cases per 1000 live births (treated 2005–2016). Mainly mild CH with normal or hyperplastic GIS.	TCH only assessed in final study period	Not due to change in TSH cut points or population ethnicity. Environmental factors, for example, iodine insufficiency, may have contributed
Hinton et al. (12)	Summary of total and state-specific data 1991–2007	USA	CH incidence increased in the United States by 3% per year; however, an increase did not occur in all states, at a constant rate, or at the same rate	Not assessed	Race, ethnicity, sex, and low birth weight/preterm birth all affected CH incidence.
Albert et al. (11)	1993–2010	New Zealand	Overall incidence of CH rose from 2.6 to 3.6 per 10 000 live births due to increased GIS CH.	Not assessed	Mainly due to altered population ethnicity. No change in TSH cut points.
Harris & Pass (10)	1978–2005	USA	Overall incidence of CH rose 73% between 1987 and 2002	Not assessed	Altered demographics account for 36–38% of the increase in incidence of CH. Diagnostic cut points unchanged.
Deladoey et al. (8)	1990–2009	Canada	Incidence of GIS CH doubled, and TD and goitre remained constant.	Not assessed	Decrease in TSH cut pojnt
Barry et al. (5)	1982–2012	France	Annual average increase of 5.1% for GIS, mild and severe. TD constant.	Not assessed	Unlikely due to change in TSH cut points or population ethnicity. Possible contribution of increased preterm birth and iatrogenic iodine overload

PCH, permanent CH; TD, thyroid dysgenesis.