Temporal Trends in Reported Malformation Incidence for
the United States - Birth Defects Monitoring Program
Godfrey P. Oakley, Jr., M.D.
Levy M. James
Larry D. Edmonds, M.S.P.H.
Birth Defects Branch
Chronic Diseases Division
Center for Environmental Health
Introduction and Methods
Reports of increased occurrence of ventricular septal defects
underscore
the importance of monitoring trends in birth defects (1t). The
Birth Defects
Monitoring Program (BDMP) is a collaborative effort involving two
governmental
agencies and two private, nonprofit organizations: The National
Institute of
Child Health and Human Development, CDC, the March of Dimes Birth
Defects
Foundation, and the Commission on Professional and Hospital
Activities (CPHA),
Ann Arbor, Michigan (2-4t). Its primary purpose is to monitor the
incidence
of birth defects and other conditions of the newborn. Data used in
this
program are included in those already sent to CPHA as part of its
Professional
Activity Study (PAS) health-data-processing system. Discharge
abstracts are
coded by hospital medical records department staff and submitted
regularly to
CPHA for data processing. Included are abstracts on all live-born
and
stillborn infants delivered in each PAS hospital. Portions of the
data
contained in abstracts on the newborn are used in the BDMP, thus
resulting in
a monitoring system that involves no added hospital costs or
reporting
responsibilities. At CPHA these data are entered into a special
data file and
used to produce monitoring reports and other tabulations. These
reports and
tabulations for PAS hospitals that agree to participate in the BDMP
are sent
to CDC for analysis. A total of 161 defect categories are analyzed
to
determine increases or other unusual trends. Currently, data on
960,184
births in 1,128 hospitals are used in the BDMP.
Although this data source is not population-based and not a
random sample
of U.S. births, it nevertheless represents the largest single
source of
uniformly collected and coded discharge data on birth defects
among newborns.
Maternal data are not routinely available through this system.
Although the
BDMP functions primarily as an early warning system, it can be
useful also for
correlating incidence patterns with such trends as the temporal and
geographic
distribution of drugs, chemicals, and other possible human
teratogens.
Results and Discussion
Noteworthy findings are the substantial unexplained increases
in rates of
ventricular septal defect (1t), patent ductus arteriosus, and renal
agenesis
(Table 1). Rh hemolytic disease incidence has substantially
decreased because
more females are receiving appropriate postpartum treatment and
also because
the average parity has decreased (Table 2). The decreases in
anencephaly and
spina bifida rates--two of the most common and serious
environmental-associated birth defects--are unexplained and do not
appear to
reflect prenatal diagnosis (5t) (Table 2). The marked decrease in
the
incidence of anophthalmos occurred primarily between 1973 and 1974,
coincident
with a general coding change; however, it is not clear whether this
is the
cause of the decrease (Table 2). Down syndrome rates remained
nearly constant
over the decade, in spite of a decline from 6% to 5% in the
proportion of
births to females 4!535 years old (6t) (Table 3). Even though this
is a
high-risk group for Down syndrome, only a small proportion of
births and cases
occur among these females, and the observed change in crude
incidence is
almost exactly that expected as a result of this change in the
maternal age
distribution. The stability of congenital rubella in the face of a
sharp
decline in clinical rubella is surprising, and there is presently
no
explanation for the disparity (Table 3).
The BDMP data must be interpreted with care but, used as a
screening
tool, they frequently call attention to areas that need additional
study.
Variations in incidence may be caused by changes other than those
associated
with environmental teratogens--for example, chance, diagnostic
habits, and
reporting procedures. These possible explanations must be
considered in
seeking the cause of a trend or geographic cluster.
References
Layde PM, Dooley K, Erickson JD, Edmonds LD. Is there an
epidemic of
ventricular septal defects in the U.S.? The Lancet
1980;1:407-8.
Oakley GP Jr. Incidence and epidemiology of birth defects.
In: Genetic
issues in pediatrics and obstetric practice. Kaback MM ed.
Chicago Year
Book Medical Publishers, Inc., 1981:25-43.
Edmonds LD, Layde PM, James LM, Flynt JW Jr, Erickson JD,
Oakley GP Jr.
Congenital malformations surveillance: two American systems.
Int J
Epidemiol 1981;10:247-52.
Windham GC, Edmonds LD. Current trends in the incidence of
neural tube
defects. Pediatrics 1982;70:333-7.
Adams MM, Erickson JD, Layde PM, Oakley GP. Down's syndrome:
recent
trends in the United States. JAMA 1981;246:758-60.
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