Preterm Birth Causes, Consequences, and Prevention (2007) / Chapter Skim
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Appendix B Prematurity at Birth: Determinents, Consequences, and Geographic Variation
Appendix B Prematurity at Birth: Determinents, Consequences, and Geographic Variation
Pages 604-643
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From page 604... ...
. The ongoing reduction in the risk of an infant death has largely been driven by improvements in birth weight- and gestational age-specific infant mortality rates stemming from advancements in intensive medical care services and technology (6–8)
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From page 605... ...
. Although low birth weight has often received greater attention than preterm birth as the leading factor underlying poor pregnancy outcomes in the United States, it has been recognized that to successfully address these problems, the "key goal is prevention of preterm birth" (23)
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. This complex array of social and medical care developments and the intractability of the present preterm birth trends necessitate the ongoing and heightened attention of health researchers, health care providers, public health practitioners, and policy makers.
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607 APPENDIX B 3,500 3,000 Preterm 2,500 Birth weight (grams) 2,000 LBW 1,500 SGA Preterm/LBW 1,000 Preterm/LBW/SGA 500 0 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 Gestational age in completed weeks FIGURE B-1 Comparison of preterm (<37 weeks of gestation)
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608 PRETERM BIRTH TABLE B-1 Gestational Ages of Live Births in the United States, 1995 to 2000 Gestational Age Category (Weeks of Gestation) Percentage of Births % Extremely Preterm (≤28)
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610 PRETERM BIRTH tion. These gestational age–based health status and health care utilization indices are useful on a population level to ensure that service needs are met, target services to at-risk populations, and evaluate the efficacies of those interventions.
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Although many pregnant women in the United States may receive an ultrasound, far fewer receive an ultrasound early enough to obtain the most reliable estimate of gestational age. Minority and impoverished women, who often face barriers to access to prenatal care services, may be less likely to obtain an early ultrasound.
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612 PRETERM BIRTH TABLE B-3 Postnatal Methods for Determining Gestational Age Method Focus of Measure weighta Birth infant size Head circumference infant size Foot length infant size Crown-heel length infant size Dubowitzb physical and neurological maturity Ballardc physical and neurological maturity Revised Ballardd physical and neurological maturity Lens vesselsd physical maturity Cranial ultrasound physical and neurological maturity Nerve conduction velocities physical and neurological maturity aStill used as a gross indicator of gestational age, although limitations are widely known. Birth weight is more typically used to assess the adequacy of growth for gestational age and as a research method to impute missing gestational age values and to identify grossly inaccurate gestational age values bBecause of a preference for the Ballard measure, this measure may have limited use in the United States.
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613 APPENDIX B Dubowitz score, the Ballard score, lens vessels, nerve conduction velocities, and cranial size by ultrasound) evaluate different aspects of infant maturity by using physical or neurological milestones that are typically observed by a certain gestational age.
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It is these studies that have typically established current national trends and international comparisons in preterm birth rates. Meanwhile, clinical studies may more typically have access to early ultrasound data, although the study populations selected may be less representative of the larger population at risk of preterm birth.
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615 APPENDIX B 12 11 10 9 8 Percentage 7 6 5 4 3 2 1 0 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 20 Years Very Preterm Preterm FIGURE B-2 Trends in maturity: percentages of deliveries to U.S. resident mothers by preterm birth category, 1980 to 2000.
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616 PRETERM BIRTH TABLE B-4 Gestational Ages of Live Births in the United States, 1985– 1988 and 1995–2000 Percentages of Births Gestational Age Categories 1985–1988 1995–2000 % Extremely Preterm (≤28 wks) 0.66 0.82 % Very Preterm (≤2 wks)
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617 APPENDIX B changes in the proportion of white multiple births and the proportions of births among older and unmarried mothers are potential contributors to these dissimilar trends in prematurity, as are changes in racial disparities in vital record reporting practices, e.g., more complete reporting of extremely preterm deliveries. Differentials in the measurement of gestational age among these groups may also be involved.
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618 PRETERM BIRTH (a) Percentages 8.0-9.9% (12)
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619 APPENDIX B 50 40 Percent 30 20 10 0 20 22 24 26 28 30 32 34 36 38 40 42 44 Gestational age in completed weeks (2 week intervals) White Black Japanese Asian Indian Samoan FIGURE B-6 Gestational age distribution of live births by race, United States, 1999 and 2000.
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620 PRETERM BIRTH (a) Percentages 8.0-9.4% (11)
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621 APPENDIX B (c) Very White, 1995 -2000 Percentages 1.5-1.74% (15)
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622 PRETERM BIRTH 25 20 15 Percent 10 5 0 20 22 24 26 28 30 32 34 36 Gestational age in completed weeks (2 week intervals) Diabetes Hypertension Smoking White total FIGURE B-9 Gestational age distribution of live births among white mothers by maternal disease group (diabetes, hypertension, and smoking)
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623 APPENDIX B 45 40 35 30 Percent 25 20 15 10 5 0 20 22 24 26 28 30 32 34 36 38 Gestational age in completed weeks (2 week intervals) Singletons Twins Triplets FIGURE B-10 Gestational age distribution of live births by multiple births, United States, 1996 to 2000.
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Risk The numerous efforts to prevent preterm birth have had little success (28–30, 55, 56)
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. Social, behavioral, stress, and maternal psychological factors have frequently been linked to pregnancy outcomes; and chronic stress has been related to low socioeconomic status (57–66)
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626 PRETERM BIRTH TABLE B-7 Possibly Mutable Risk Factors Associated with Preterm Birth No or inadequate prenatal care usage Cigarette smoking Use of marijuana and other illicit drugs Cocaine use Alcohol consumption Caffeine intake Maternal weight gain Dietary intake Sexual activity during late pregnancy Leisure-time physical activities Chronic stressors may include financial insecurities, poor and crowded living conditions, unemployment, stressful working conditions, domestic violence, and unsatisfying marital relationships. Many of these risk factors are multifactorial and are deeply intertwined with social class, culture, race, and ethnicity.
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resident births. Considerable variation in the mortality risk of these high risk infants is apparent.
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628 PRETERM BIRTH TABLE B-8 Risk Factors for Preterm Birth 1980–1984 1985–1989 % Total OR ARtotal % Total OR ARtotal % Among % Among Preterm Preterm Births Births Factor % Preterm % Preterm Total % Preterm 9.1 9.8 Age in teens 5.3 1.3 3.9 4.6 1.20 3.2 8.7 (1.29– 7.6 (1.19– 1.31)
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629 APPENDIX B 1990–1994 1995–1999 % Total OR ARtotal % Total OR ARtotal % Among % Among Preterm Preterm Births Births % Preterm % Preterm 10.6 11.1 5.0 1.21 2.6 4.8 1.17 1.8 7.3 (1.19– 6.5 (1.16– 15.7 1.23)
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630 PRETERM BIRTH TABLE B-8 Continued 1980–1984 1985–1989 % Total OR ARtotal % Total OR ARtotal % Among % Among Preterm Preterm Births Births Factor % Preterm % Preterm Multiple births 2.0 8.55 7.4 2.2 9.28 8.4 9.3 (8.48– 10.3 (9.21– 41.7 8.62)
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From page 631... ...
, advances in medical technology (e.g., the greater use of ART, leading to more multiple births) , and developments in medical practice (e.g., a greater willingness of obstetricians and maternal-fetal medicine specialists to intervene and deliver high-risk fetuses earlier in pregnancy because of earlier entry into prenatal care, leading to the earlier identification of highrisk conditions, coupled with the development and availability of therapies, including surfactant and steroids, and perinatal and neonatal care for high
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632 PRETERM BIRTH 20 19 18 17 16 Preterm Very Preterm 15 14 13 12 Percent 11 10 9 8 7 6 5 4 3 2 1 0 5 -7 -9 -1 -3 -5 -7 -9 -1 -3 -5 -7 -9 + <1 40 16 18 20 22 24 26 28 30 32 34 36 38 Age ofof Mother Age mother FIGURE B-13 Percentages of preterm and very preterm births by age of the mother, 1995 to 2000. Source: 1985–1988 and 1995–2000 Birth Cohort Linked Birth/ Infant Death Data Set, CD-ROM Series 20, USDHHS, CDCP, NCHS; 1980–2000 Natality Data Set, CD-ROM Series 21, USDHHS, CDCP, NCHS.
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. Preterm birth prevention programs, which often involve social support and patient education, have also been proposed and implemented but have shown little success (28, 30)
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634 PRETERM BIRTH deliveries by state, 1995 Rate per 1000 live birth 28.4-35.0 (16)
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635 APPENDIX B 1000 Mortality rate per 1000 live births 100 (log scale) 10 1 22 24 26 28 30 32 34 36 38 40 42 44 Gestational age categories (2-week intervals)
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636 PRETERM BIRTH Several specific reporting issues may affect trends and variations in preterm birth rates. These include changes or differences in: • the reporting of deliveries of infants weighing <500 grams as either a miscarriage, a fetal death, or a live birth; • the definition of fetal death involving birth weight and gestational age criteria; • the measurement of gestational age, e.g., by the use of LMP and clinical estimates; and • reporting regulations, procedures, processes, training, and quality at hospitals and by state and local jurisdictions.
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637 APPENDIX B to estimate gestational age, e.g., ultrasound or LMP. Some nations may rely on periodic surveys rather than vital records to establish preterm birth rate trends.
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Advances in neonatal care include high-frequency ventilation, surfactant, and postnatal steroids. Regionalization of high-risk perinatal services facilitates appropriate access to these obstetric and neonatal intensive care services.
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Trends and racial differences in birth weight and related survival. Maternal Child Health J 1999; 3(1)
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Advances in the Prevention of Low Birth Weight Pro ceedings of an International Symposium. Washington, DC: National Center for Educa tion in Maternal and Child Health, 1991.
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641 APPENDIX B 35. Klebanoff MA, Shiono PA.
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Intrauterine growth retardation and premature delivery: the influence of maternal smoking and psychosocial factors. Am J Public Health 1996; 86:347–354.
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643 APPENDIX B 79. Region IV Network for Data Management and Utilization.
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