title: Trends in incidence rates of congenital hypothyroidism related to select demographic factors: data from the United States, California, Massachusetts, New York, and Texas.
abstract: Primary congenital hypothyroidism (CH) is a common and preventable cause of intellectual disability. The incidence rate of CH has been reported to be increasing in the United States, but the factors behind the observed rate increase are not known. We summarize here the data presented at a workshop on CH, at which factors potentially related to the CH-incidence-rate increase (namely, race, ethnicity, sex, and birth outcomes) were evaluated. Data sources for the analyses included a national data set of newborn-screening results and state-specific data from newborn-screening programs in California, Massachusetts, New York, and Texas. The incidence rate of CH increased in the United States by 3% per year; however, an increase did not occur in all states, at a constant rate, or even at the same rate. Analysis of US data (1991-2000) showed a CH-incidence-rate increase only among white newborns. More recently, in California (2000-2007), the rate was constant in non-Hispanic newborns, but it increased among Hispanic newborns. In the national data, the CH-incidence rate increased similarly among boys and girls, whereas in Texas (1992-2006), the rate among boys increased significantly more than among girls and varied according to race and ethnicity. In Massachusetts (1995-2007), low birth weight newborns or newborns who had a delayed rise in thyrotropin concentration accounted for the majority of the recent rate increase. Race, ethnicity, sex, and pregnancy outcomes have affected the observed increasing incidence rate of CH, although there have been some inconsistencies and regional differences. The association with preterm birth or low birth weight could reflect the misclassification of some cases of transient hypothyroxinemia as true CH. Future studies of risk factors should focus on correct initial identification and reporting of demographic characteristics and pregnancy outcomes for cases of CH. In addition, long-term follow-up data of presumed cases of CH should be ascertained to differentiate true cases of CH from cases of transient hypothyroidism.
authors.affiliation: Division of Birth Defects and Developmental Disabilities, National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, Atlanta, Georgia 30333, USA. chinton@cdc.gov
authors.forename: Cynthia F
authors.initials: CF
authors.lastname: Hinton
authors.forename: Katharine B
authors.initials: KB
authors.lastname: Harris
authors.forename: Lynette
authors.initials: L
authors.lastname: Borgfeld
authors.forename: Margaret
authors.initials: M
authors.lastname: Drummond-Borg
authors.forename: Roger
authors.initials: R
authors.lastname: Eaton
authors.forename: Fred
authors.initials: F
authors.lastname: Lorey
authors.forename: Bradford L
authors.initials: BL
authors.lastname: Therrell
authors.forename: Jill
authors.initials: J
authors.lastname: Wallace
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Pass
mesh_terms: D002140:California / Q000453:epidemiology; D003409:Congenital Hypothyroidism / Q000453:epidemiology*; D005260:Female; D006630:Hispanic or Latino / Q000706:statistics & numerical data; D006801:Humans; D015994:Incidence; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D007234:Infant, Premature; D008297:Male; D008404:Massachusetts / Q000453:epidemiology; D009518:New York / Q000453:epidemiology; D016017:Odds Ratio; D011247:Pregnancy; D011256:Pregnancy Outcome; D012737:Sex Factors; D013781:Texas / Q000453:epidemiology; D013972:Thyrotropin / Q000097:blood; D014481:United States / Q000453:epidemiology
chemical_list: D013972:Thyrotropin