Extremely Low Birth Weight and Infant Mortality Rates in the United States WHAT’S KNOWN ON THIS SUBJECT: Infant and neonatal mortality rates in the United States decreased markedly during the twentieth century but have not decreased notably during recent years. There has been an increase in preterm and low birth weight births in recent years. WHAT THIS STUDY ADDS: The lack of decrease in infant and neonatal mortality rates in recent years is due in large part to the increasing proportion of preterm and low birth weight infants, particularly infants ,500 g. abstract OBJECTIVE: Infant mortality rates (IMR) and neonatal mortality rates (NMR) in the United States have not decreased recently. The purpose of this study was to determine the contributions of birth weight and gestational age subgroups to the IMR and NMR in the United States. METHODS: We used the most recent (1983–2005) US linked birth and infant death data and simple regression analysis to determine the contributions of specific birth weight and gestational age subgroups to trends in IMR and NMR. RESULTS: IMR and NMR decreased between 1983 and 2005 for all birth weight and gestational age subgroups. There was an increase in births of very low birth weight infants from 1.2% to 1.5% (P , .001) over this period. The proportion of very low birth weight–infant deaths in- creased from 42.9% to 54.8%, resulting in recent nonsignificant declines in IMR and NMR. The proportion of live-birth infants ,500 g increased from 0.12% to 0.18% (P , .001). The adjusted IMR and NMR over time (excluding infants ,500 g) have steeper declining trends than the ones including infants ,500 g. The changes in overall IMR and NMR in recent years (2000–2005) are not statistically significant. However, the adjusted IMR and NMR trends during this time are highly significant. CONCLUSIONS: The increased proportions of infants ,500 g and other low birth weight infants contribute greatly to the lack of a decrease in IMR and NMR from 2000 to 2005, although birth weight– and gesta- tional age–specific IMR and NMR continue to decrease. Pediatrics 2013;131:855–860 AUTHORS: Carissa Lau, a Namasivayam Ambalavanan, MD, a Hrishikesh Chakraborty, DrPH, b Martha S. Wingate, DrPH, c and Waldemar A. Carlo, MD a a Department of Pediatrics, University of Alabama at Birmingham, and Children’ s of Alabama, Birmingham, Alabama; b Department of Epidemiology and Biostatistics, University of South Carolina, Columbia, South Carolina; and c Department of Health Care Organization and Policy, School of Public Health, University of Alabama at Birmingham, Birmingham, Alabama KEY WORDS birth rate trends, infants, infant mortality trends, vital statistics, low birth weight, prenatal care delivery, United States epidemiology ABBREVIATIONS IMR—infant mortality rates NMR—neonatal mortality rates VLBW—very low birth weight Ms Lau assisted in the conceptualization and design of the study, carried out the initial analysis, designed data collection instruments, collected data, critically reviewed the manuscript, and approved the final manuscript as submitted; Dr Ambalavanan designed data collection instruments, collected data, critically reviewed the manuscript, and approved the final manuscript as submitted; Dr Chakraborty assisted in the conceptualization and design of the study, carried out the initial analysis, designed data collection instruments, critically reviewed the manuscript, and approved the final manuscript as submitted; Dr Wingate assisted in the conceptualization and design of the study, critically reviewed the manuscript, and approved the final manuscript as submitted; and Dr Carlo conceptualized and designed the study, drafted the initial manuscript, designed data collection instruments, collected data, critically reviewed the manuscript, and approved the final manuscript as submitted. www.pediatrics.org/cgi/doi/10.1542/peds.2012-2471 doi:10.1542/peds.2012-2471 Accepted for publication Feb 1, 2013 Address correspondence to Waldemar A. Carlo, MD, Department of Pediatrics, University of Alabama at Birmingham, 9380 Women and Infants Center, 1700 6th Avenue South, Birmingham, AL 35249- 7335. E-mail: wcarlo@peds.uab.edu PEDIATRICS (ISSN Numbers: Print, 0031-4005; Online, 1098-4275). Copyright © 2013 by the American Academy of Pediatrics FINANCIAL DISCLOSURE: The authors have indicated they have no financial relationships relevant to this article to disclose FUNDING: Supported by a grant from the Perinatal Health and Human Development Program of the University of Alabama at Birmingham and the Children’ s of Alabama Centennial Fund. PEDIATRICS Volume 131, Number 5, May 2013 855 ARTICLE by guest on April 29, 2016 Downloaded from