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APPENDIX D
Notes on National Data Available to
Study Low Birthweight Trends and
to Monitor Related Programs
In studying the problem of low birthweight, the committee has
reviewed a variety of national data sets to understand broad trends in
low birthweight, its relationship to mortality and morbidity, and the
extent to which certain public programs affect its incidence. Several
such data sets are outlined in the section below, followed by a section
noting some of the problems with these systems. The topic of data
availability also is raised in other parts of the report, particularly
in chapters 3 and 7.
The committee has made no detailed recommendations about how best
to strengthen the data systems in this area. However, it does wish to
stress how important it is for the nation to maintain and strengthen
its data collection systems pertinent to low birthweight and other
important health topics. Understanding, and in turn preventing, low
birthweight requires fully adequate data on a broad range of factors:
demographic, medical, behavioral, socioeconomic, programmatic, and
others. Budgetary constraints should not be allowed to undermine
existing systems. Instead, an increased commitment should be made to
ensuring that adequate data are collected, analyzed, and reported in a
useful and timely manner. Both state and national data systems merit
support because high quality data are needed at both levels, and
because many national data sets are developed from information
collected by states and localities.
Data Sources
National data on the incidence of low birthweight and on other
maternal/infant characteristics are available from the National Center
for Health Statistics' (NCHS) Vital Statistics Registration System
{VSRS), which continuously collects and compiles data from birth
certificates. The VSRS provides data on the incidence of low
birthweight tabulated by race, sex of infant, plurality (single births,
twins, etc.), birth order of infant, and by mother's age, educational
attainment, marital status, receipt of prenatal care, and interval
since last birth. Data from the VSRS are published annually in an
abbreviated form in the "Advance Report of Final Natality Statistics"
275
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276
section of the NCHS Monthly Vital Statistics Report series. More
complete data are available later in another annual NCHS publication,
Vital Statistics of the United States, Vol. I, Natality.
Supplemental information on the incidence of low birthweight by
characteristics beyond those covered on the birth certificate
. . . . _ . . _ —
is
avaz~aDIe from Me National Natat~ty Fottow-nacx surveys, periodically
conducted by NCHS. Based on questionnaires mailed to mothers,
hospitals, physicians, and other health care providers, these surveys
provide birth data by characteristics such as mother's occupation and
work history during pregnancy, father 's occupation, source of medical
care for mother and infant, funnily income, mother 's smoking and
drinking habits, and whether the baby is breast or bottle fed. To
date, ACES has conducted National Natality Surveys (NNS) from 1963
through 1969, and In 1972 and 1980. The next NNS data collection is
scheduled to start in 1988. NCHS hopes to conduct subsequent National
Natality Surveys at 4-year intervals. Data from the NNS are available
in a variety of publications, including Vital and Health Statistics
Series reports and supplements to the Monthly Vital Statistics Report.
A dozen articles from the 1980 NNS have been published in Health:
united states 1983 ~ and in the Mar ch-ADr il 1984 ~ ssue of Public
Health Reports. Public use data tapes of the fol low-back surveys
are also available from the National Technical Information Service.
Although they are far from current, two other sources of national
low birthweight data should be noted, both specie' studies by NCES:
the NCHS Linked Birth/Death Certificate Study based on the 1960 birth
cohort;3 and the 1964-1966 National Natality and Infant Mortality
Survey, 4 which related low birthweight to infant mortality using
estimates from two separate surveys rather than linked birth/death
records.
Data Needs
A major problem with national data relevant to low birthweight is
the absence of data on the sequelae of low birthweight drawn from a
nationally representative sample of births. At present, neither the
VSRS nor the NNS provides information on morbidity or mortality
associated with low birthweight. According to NCHS and the Centers for
Disease Control (CDC) , no national data system is currently being
planned to look systematically at the relationship between low
birthweight and subsequent morbidity. Efforts are being made, however,
to address the need for data relating low birthweight to mortality.5 6
NCHS has undertaken the "1980 National Natality Survey/National
Death Index Match" project, a special supplemental study that will
search and compare the 1980 and 1981 National Death Index with an NNS
sample of nearly 10,000 liveborn infants. Although the numbers are
small (based on the NNS over sampling of low birthweight infants, it is
projected that 271 of the NNS infants will have died in their first
year of lifer, the match will be able to report infant mortality rates
by birthweight, as well as by several hundred other data items included
on the NNS. s
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277
In the near future, NCHS hopes to undertake a pilot program to
develop a national linked birth and death certificate file for the 1982
and 1983 birth cohorts. The addition of linked files to ongoing NCHS
data systems will be evaluated at the end of the pilot study. Finally,
it is hoped, but not yet definite, that NCHS will conduct an Infant
Mortality Follow-back Survey in 1988 to accompany the National Natality
Survey.5
As an interim effort, CDC plans to compile linked birth and death
certificate data from individual states. Current plans are to use the
1980 birth cohort. States will be asked to provide data on infant
deaths by birthweight for the following characteristics: maternal age,
number of previous live births, number of fetal deaths (terminations of
pregnancy of 20 or more weeks gestation), level of maternal education,
sex of infant, gestational age at birth, and type of delivery. The
states also will be asked to provide data on cause of death by
birthweight for neonatal and postneonatal deaths. Finally, CDC will
request data on infant deaths by gestational age according to month
prenatal care began and number of prenatal visits. All of the above
information will be requested for all infants, and separately for black
and for white infants. CDC plans to have the results of the study
available by the spring of 1985. Once the NCHS linked birth/death
certificate data collection system is under way, CDC data collection in
this area probably will be phased out.6
A second shortcoming of the national data currently available is
the considerable time lag between the end of a calendar year and
publication of final national data for that year. There is a lag of
approximately 2 years before publication of the rather abbreviated
"Advance Report of Final Natality Statistics,. and an interval of 3 to
4 years before publication of Vital Statistics of the United States.
It is hoped that national linked birth/death certificate data for any
given birth cohort will become available within 4 years or less after
the year of birth. For purposes of evaluation, planning, and
implementation of public policies, this relatively long lag makes it
difficult to use national low birthweight data in a timely manner.
Third, national low birthweight data by income (or class, as the
British use) are very limited. While the NNS does provide periodic
data by income, the VSRS does not collect information by income or
socioeconomic status . AS a result, surrogate measures such as race or
mother's education are often used, making it more difficult to
determine the extent to which low birthweight is associated with
poverty as distinct from other factors.
Fourth, while the NNS has collected information from married
mothers on sources of family income including participation in public
programs, there is no national data base that systematically and
regularly links low birthweight data (incidence and outcome) to
participation in public programs such as the Special Supplemental Food
Program for Women, Infants and Children (WIC), Medicaid, Food Stamps,
and Aid to Families with Dependent Children. ThiS information, if
linked with data on income or socioeconomic status, would be
particularly useful in evaluating the impact of public policies and
programs.
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278
Finally, national data by ethn~city are less complete than they
might be. The NNS does collect detailed ethn~city data, which are
available on public use data tapes; however, the NNS is conducted
relatively infrequently. While the VSRS currently collects data by
ethnicity, reporting by states is quite uneven. National data on
births of Hispanic parentage were first available from a 1978 cohort,
based on reporting from 17 states. 7 By 1980, 22 states reported on
this population.8 Low birthweight data on births of Asian parentage
(Chinese, Filipino, Japanese, Hawaiian, and other) were first published
by NCHS in 1984, and were based on the 1980 birth cohort.9
Re fer ences
National Center for Health Statistics: Health, United States,
1983, pp. 19 - 434. DHES No. (PHS) 84-1232. Public Health Service.
Washington, D.C.: U.S. Government Printing Office, December 1983.
2 . Public Health Reports. 99 :111-183, March-April 1984.
3. National Center for Health Statistics: A Study of Infant Mortality
_ ,
-
from Linked Records, by Birth Weight, Period of Gestation, and
Other variables, United States. Vital and Health Statistics,
Series 20, No. 12. DHEW No. (HSM) 72-1055. Health Services and
Mental Health Administration . Washington , D.C.: U. S . Government
Pr dinting Off ice, May 1972 .
National Center for Health Statistics: Infant Mortality Rates:
Socioeconomic Factors, United States. Prepared by B MacMahon, MG
Kovar, and JJ Feldman. Vital and Health Statistics, Series 22, No.
14. DHEW No. (HSM) 72-1045. Health Services and Mental Health
Administration. Washington, D.C.: U.S. Government Printing Office,
March 197 2 .
Robert Israel, Deputy Director, National Center for Health
Statistics, Hyattsville, Md . Per sonal communication, 1984 .
Carol JR Hogue, Chief, Pregnancy Epidemiology Branch, Division of
Reproductive Health, Centers for Disease Control, Atlanta, Ga.
Personal Communication, 1984.
7. National Center for Health Statistics: Births of Hispanic
Parentage, 1978. Prepared by S Ventura and R Heuser. Monthly
Vital Statistics Report, Vol. 29, No. 12 (supplement) . DHHS No.
(PHS) 81-1120 . Public Health Service. Washington, D.C .: U. S.
Government Printing Office, March 1981.
8. National Center for Health Statistics: Births of Hispanic
Parentage, 1980. Prepared by S Ventura. Monthly Vital Statistics
Report, irol. 32, No. 6 (supplement). DHHS No. (PHS) 83-1120.
Public Health Service. Washington, D.C.: U.S. Government Printing
Office, September 1983.
9. National Center for Health Statistics: Character istics of Asian
Births: United States, 1980. Prepared by S Taffel. Monthly Vital
Statistics Report, Vol. 32, No. 10 (supplement). DHHS No. (PHS)
84-1120 . Public Health Service. Washington, D.C .: U. S. Government
Pr inting Off ice, February 1984 .
Representative terms from entire chapter:
national data
