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Historical Trends in Low Birth Weight

Historical Trends in Low Birth Weight Scholars have noted that the premature birth rate has risen steadily in the United States during the past 25 years and have used this fact to try to understand the cause of premature birth.1 As part of an on-going epidemiologic review of the history of the etiology of intellectual disability, we examined trends in low-birth-weight births in the United States during the last 5 decades. Methods Our methods have been described previously.2 We identified medical conditions associated with intellectual disability, in this case premature birth, then used a common set of variables to construct estimates of the condition-specific prevalence of intellectual disability during the last 50 years. For preterm births, we began our data collection at 1950, when international consensus accepted low birth weight as the best measure of prematurity.3 Prior to 1950, gestational age, weight gained by the mother, and other factors were used to determine maturity at birth. In 1950 nearly all states began to include birth weight data on certificates of live birth. (Connecticut required reporting birth weight in 1957, Massachusetts in 1959.) Although each state uses different forms and follows different statutes, there is a high degree of uniformity in the live-birth records, and all data are reported to the National Center for Health Statistics. The center has released data on low birth weight with respect to the total births in the corresponding year since 1950.3-5 Data by gestational age are also available, but we chose birth weight because determining birth weight is more precise than gestational age, and as late as 1967, Massachusetts and parts of Maryland did not record gestational age on live-birth forms. In these data sets, birth weight is divided into 4 categories: 1000 g or less, 1001 to 1500 g, 1501 to 2000 g, and 2001 to 2500 g. We defined low birth weight as birth weight between 1501 and 2500 g, and very low birth weight as 1500 g or less. We calculated incidence by each birth weight category as a percent of total births for a given year, then plotted the incidence of prematurity across a 55-year period. Data include singleton and multiple births. Results The Figure shows the incidence of very-low-birth-weight births, low-birth-weight births, and combined incidence as a function of time from 1950 through 2005. The incidence of birth weights less than 1000 g and those between 1000 and 1500 g follow the same sinusoidal pattern as the 1500- to 2500-g births when plotted on a longer y-axis. Figure. View LargeDownload Incidence of low birth weight: 1950 to 2005. Comment Attempts to understand the causes of premature birth generally rely on epidemiological data that start in 1980 and suggest a steady rise during the last 25 years. We found that the incidence of prematurity, as measured by low birth weight, first peaked in the mid-1960s then reached a nadir in the late 1970s before beginning to increase in the last 3 decades. We did not find evidence of systematic changes in reporting practices that would account for this pattern, which follows the overall pattern of the number of total births in the United States since 1950. There is little evidence that changes in reporting have had a significant effect on the rate of low birth weight derived from birth certificate data.6 We did not investigate the many potential factors that may explain this pattern, such as trends in obstetrical or neonatal care, access to health care through Medicaid, or maternal characteristics like age or race/ethnicity. We do suggest that attempts to explain trends in low-birth-weight births might benefit from recognizing the pattern during the last 5 decades and not merely the rise since 1980. Correspondence: Dr Brosco, Department of Pediatrics, University of Miami, PO Box 016820 (D-820), Miami, FL 33101 (jbrosco@miami.edu). Author Contributions: All of the authors had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: Brosco, Sanders, Guez, and Lantos. Acquisition of data: Guez. Analysis and interpretation of data: Brosco, Sanders, and Guez. Drafting of the manuscript: Brosco, Sanders, Guez, and Lantos. Critical revision of the manuscript for important intellectual content: Brosco, Sanders, Guez, and Lantos. Statistical analysis: Sanders. Administrative, technical, and material support: Brosco and Guez. Study supervision: Brosco. Financial Disclosure: None reported. Funding/Support: This study was supported by grant 033954 from the Robert Wood Johnson Foundation General Scholar Program (Dr Brosco) and the Department of Health and Human Services/Health Resources and Services Administration/Maternal and Child Health Bureau Advisory Committee on Heritable Disorders and Genetic Diseases in Newborns and Children (Dr Brosco). Role of the Sponsors: Other than funding, the sponsors had no role in the design or conduct of the study; the collection, analysis, or interpretations of the data; or in the preparation, review, or approval of the manuscript. References 1. Behrman RedStith Butler Aed Preterm Birth: Causes, Consequences, and Prevention. Washington, DC National Academies Press2007; 2. Brosco JPMattingly MSanders LM Impact of specific medical interventions on reducing the prevalence of mental retardation. Arch Pediatr Adolesc Med 2006;160 (3) 302- 309PubMedGoogle ScholarCrossref 3. Chase HByrnes M Trends in “prematurity” United States: 1950-1968. Vital Health Stat. 1972;3 (15) Google Scholar 4. National Center for Health Statistics, Vital Statistics of the United States, Volume I: Natality. Atlanta, GA US Government Printing Office1968-1989; 5. National Vital Statistics Center, Gestation and Birth Weight Tables: Centers for Disease Control and Prevention; 1990-2005 6. MacDorman MFMartin JAMathews TJHoyert DLVentura SJ Explaining the 2001-02 infant mortality increase: data from the linked birth/infant death data set. Natl Vital Stat Rep 2005;53 (12) 1- 22PubMedGoogle Scholar http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Pediatrics & Adolescent Medicine American Medical Association

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Publisher
American Medical Association
Copyright
Copyright © 2010 American Medical Association. All Rights Reserved.
ISSN
1072-4710
eISSN
1538-3628
DOI
10.1001/archpediatrics.2009.255
Publisher site
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Abstract

Scholars have noted that the premature birth rate has risen steadily in the United States during the past 25 years and have used this fact to try to understand the cause of premature birth.1 As part of an on-going epidemiologic review of the history of the etiology of intellectual disability, we examined trends in low-birth-weight births in the United States during the last 5 decades. Methods Our methods have been described previously.2 We identified medical conditions associated with intellectual disability, in this case premature birth, then used a common set of variables to construct estimates of the condition-specific prevalence of intellectual disability during the last 50 years. For preterm births, we began our data collection at 1950, when international consensus accepted low birth weight as the best measure of prematurity.3 Prior to 1950, gestational age, weight gained by the mother, and other factors were used to determine maturity at birth. In 1950 nearly all states began to include birth weight data on certificates of live birth. (Connecticut required reporting birth weight in 1957, Massachusetts in 1959.) Although each state uses different forms and follows different statutes, there is a high degree of uniformity in the live-birth records, and all data are reported to the National Center for Health Statistics. The center has released data on low birth weight with respect to the total births in the corresponding year since 1950.3-5 Data by gestational age are also available, but we chose birth weight because determining birth weight is more precise than gestational age, and as late as 1967, Massachusetts and parts of Maryland did not record gestational age on live-birth forms. In these data sets, birth weight is divided into 4 categories: 1000 g or less, 1001 to 1500 g, 1501 to 2000 g, and 2001 to 2500 g. We defined low birth weight as birth weight between 1501 and 2500 g, and very low birth weight as 1500 g or less. We calculated incidence by each birth weight category as a percent of total births for a given year, then plotted the incidence of prematurity across a 55-year period. Data include singleton and multiple births. Results The Figure shows the incidence of very-low-birth-weight births, low-birth-weight births, and combined incidence as a function of time from 1950 through 2005. The incidence of birth weights less than 1000 g and those between 1000 and 1500 g follow the same sinusoidal pattern as the 1500- to 2500-g births when plotted on a longer y-axis. Figure. View LargeDownload Incidence of low birth weight: 1950 to 2005. Comment Attempts to understand the causes of premature birth generally rely on epidemiological data that start in 1980 and suggest a steady rise during the last 25 years. We found that the incidence of prematurity, as measured by low birth weight, first peaked in the mid-1960s then reached a nadir in the late 1970s before beginning to increase in the last 3 decades. We did not find evidence of systematic changes in reporting practices that would account for this pattern, which follows the overall pattern of the number of total births in the United States since 1950. There is little evidence that changes in reporting have had a significant effect on the rate of low birth weight derived from birth certificate data.6 We did not investigate the many potential factors that may explain this pattern, such as trends in obstetrical or neonatal care, access to health care through Medicaid, or maternal characteristics like age or race/ethnicity. We do suggest that attempts to explain trends in low-birth-weight births might benefit from recognizing the pattern during the last 5 decades and not merely the rise since 1980. Correspondence: Dr Brosco, Department of Pediatrics, University of Miami, PO Box 016820 (D-820), Miami, FL 33101 (jbrosco@miami.edu). Author Contributions: All of the authors had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: Brosco, Sanders, Guez, and Lantos. Acquisition of data: Guez. Analysis and interpretation of data: Brosco, Sanders, and Guez. Drafting of the manuscript: Brosco, Sanders, Guez, and Lantos. Critical revision of the manuscript for important intellectual content: Brosco, Sanders, Guez, and Lantos. Statistical analysis: Sanders. Administrative, technical, and material support: Brosco and Guez. Study supervision: Brosco. Financial Disclosure: None reported. Funding/Support: This study was supported by grant 033954 from the Robert Wood Johnson Foundation General Scholar Program (Dr Brosco) and the Department of Health and Human Services/Health Resources and Services Administration/Maternal and Child Health Bureau Advisory Committee on Heritable Disorders and Genetic Diseases in Newborns and Children (Dr Brosco). Role of the Sponsors: Other than funding, the sponsors had no role in the design or conduct of the study; the collection, analysis, or interpretations of the data; or in the preparation, review, or approval of the manuscript. References 1. Behrman RedStith Butler Aed Preterm Birth: Causes, Consequences, and Prevention. Washington, DC National Academies Press2007; 2. Brosco JPMattingly MSanders LM Impact of specific medical interventions on reducing the prevalence of mental retardation. Arch Pediatr Adolesc Med 2006;160 (3) 302- 309PubMedGoogle ScholarCrossref 3. Chase HByrnes M Trends in “prematurity” United States: 1950-1968. Vital Health Stat. 1972;3 (15) Google Scholar 4. National Center for Health Statistics, Vital Statistics of the United States, Volume I: Natality. Atlanta, GA US Government Printing Office1968-1989; 5. National Vital Statistics Center, Gestation and Birth Weight Tables: Centers for Disease Control and Prevention; 1990-2005 6. MacDorman MFMartin JAMathews TJHoyert DLVentura SJ Explaining the 2001-02 infant mortality increase: data from the linked birth/infant death data set. Natl Vital Stat Rep 2005;53 (12) 1- 22PubMedGoogle Scholar

Journal

Archives of Pediatrics & Adolescent MedicineAmerican Medical Association

Published: Jan 4, 2010

Keywords: low birth weight infant

References