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#410 - Birth Defects -- Part 1, 05-Oct-1994

The Birth Defects Monitoring Program (BDMP) is a U.S. government effort
to monitor birth defects (congenital malformations) using data
collected when newborn infants are discharged from the hospital.[1] The
BDMP was initiated by the federal Centers for Disease Control (CDC) in
1974. The current BDMP database includes information on roughly 15
million births that have occurred at 1200 predominantly mid-sized
community hospitals in the U.S. during the past 20 years.

The BDMP database is not comprehensive (it does not include information
on every birth that occurs in the U.S.). Neither does it represent a
randomly-selected sample of all U.S. births; therefore data from the
BDMP cannot be considered representative of the entire "universe" of
all U.S. newborns. In 1987 the BDMP received information on 15% of all
U.S. births, which gives an idea of how comprehensive the coverage is.
Because the data are mostly from mid-sized hospitals, we might expect
that some of the largest hospitals in the largest cities are under-
represented. Nevertheless, as the CDC says, the BDMP "represents the
largest single set of uniformly collected and coded discharge data on
congenital malformations in the United States." It is simply the best
information available on birth defects in the U.S.

CDC says that the BDMP "functions primarily as an early warning system;
however it can be useful also for correlating incidence [occurrence]
patterns with such trends as the temporal [time-related] and geographic
distribution of drugs, chemicals, and other possible human teratogens."
A teratogen (from the Greek words meaning "monster producing") is
anything that causes birth defects. Examples of teratogens are diseases
such as German measles; infections; inherited genetic defects;
radiation; and certain chemicals.

In 1990, researchers looked for trends in the BDMP database, examining
records for 38 types of birth defects from 1979-80 through 1986-87.
During this 7-year period, of the 38 types of birth defects, 29
increased; 2 decreased; and 7 remained stable (meaning they changed
less than 2% per year during the 7-year period.)

Table 1 shows the annual percent change for 30 types of birth defects.
All of them increased during the 7-year period (though some increased
at a rate less than 2% per year, and are thus classified as "stable" by
the CDC).

Table 1 contains 3 columns of numbers. The first two columns show the
actual number of birth defects per 10,000 births; the first column
shows data for the earlier period, 1979-80; the second column shows the
later period, 1986-87. The third column shows the yearly percentage
increase during the 7-year period.

Some of these increases are explained by better health care and better
diagnosis. For example, some of the heart defects listed in Table 1 are
so serious that an infant might not have survived such a defect 10
years ago but might survive it today. Likewise, some of the heart
defects might be revealed by high-tech medical diagnostic machines
today, whereas they might have gone unnoticed 10 years ago.

However, many of the increases in birth defects in Table 1 cannot be
explained by better health care or better diagnosis. If a child were
born 10 years ago with the iris missing from one or both of its eyes,
chances are good that the mother or her doctor or a nurse would see it.
(The iris is the part of the eye that makes blue eyes blue and brown
eyes brown.) So the 5.2% ANNUAL INCREASE in "aniridia" (absence of an
iris) is very likely a real increase.

The same can be said for birth defects of the central nervous system,
facial clefts, musculoskeletal defects and some of the gastrointestinal
and genitourinary defects. Most of these defects are so obvious that
they would have been noticed as easily 10 years ago as today.
Therefore, increases in these defects are very likely real increases.

Some of the increases shown in Table 1 are surprisingly large. For
example, coloboma of the eye increased 9.6% each year during the 7-year
period; this means the occurrence of this defect doubled during the
study period. (Coloboma of the eye means a wedge-shaped piece is
missing from the iris, or some other part of the eye is missing.) Other
eye disorders (congenital cataract, for example) are increasing about
5% each year, thus doubling every 14 years. (The relation-ship of
annually-increasing quantities to the doubling time was detailed in
REHW #197 and #199.)

Are most birth defects caused by the parents' genetic characteristics,
or by something in the environment?

In July of this year an important study of birth defects in Norway
appeared in the NEW ENGLAND JOURNAL OF MEDICINE.[2] It indicated that
environmental factors may be more important than previously thought.

Norway has maintained a Medical Birth Registry since 1967; the registry
now contains data on 1.5 million births. Norwegian and American
researchers examined records of 371,933 women who had given birth to
first and second children in Norway between 1967 and 1989. For the 9192
women whose first infant had a birth defect, they examined the risk of
similar or dissimilar effects in the second infant. And they examined
the risk of a birth defect in the second child among mothers who lived
in the same municipality during both pregnancies vs. mothers who moved
to a new municipality before the second child was born. (The control
group was the 362,741 women whose first infant did not have a birth

The researchers found that 2.5% of all infants born in Norway have a
birth defect. Examining 23 different kinds of birth defects, they found
that in every category, mothers whose first infant had a defect were
more likely to have a second infant with a defect, as would be expected
if birth defects are genetic in origin. What was "surprising" to the
researchers was that women who moved to a new city between pregnancies
were only half as likely to have a second child with a birth defect.
Mothers whose first child had a defect were 11.6 times as likely to
have a second child with a defect (compared to mothers whose first
child did not have a defect), but if a mother moved to a new
municipality between pregnancies she was only 5.1 times as likely to
have a second child with a defect. The researchers concluded, "...[W]e
find strong, if indirect, evidence... suggesting that important
environmental teratogens have yet to be discovered."

--Peter Montague


[1] Larry D. Edmonds, "Temporal Trends in the Prevalence of Congenital
Malformations at Birth Based on the Birth Defects Monitoring Program,
SURVEILLANCE SUMMARIES Vol. 39, No. SS-4 (Dec., 1990), pgs. 19-23.

[2] Rolv Terje Lie and others, "A Population-Based Study of the Risk of
Recurrence of Birth Defects," NEW ENGLAND JOURNAL OF MEDICINE Vol. 331,
No. 1 (July 7, 1994), pgs. 1-4.

. TABLE 1 Birth Defects: Annual Percent Change in Occurrence During
7-year Period, 1979-80 to 1986-87, United States
. Annual . Number of Percent . defects per change in DEFECT
TYPE 10,000 births occurrence, . ------------------ 1979-80 to .
1979-80 1986-87 1986-87 CENTRAL NERVOUS SYSTEM Hydrocephalus without
spina bifida . (fluid in the skull) 4.34 5.84 4.3% Encephalocele (gap
in the skull) 1.10 1.16 0.8% Microcephalus (small head) 2.12 2.61
3.0% . EYES Anophthalmos (absence of eyes) 0.57 0.68 2.6% Congenital
cataract . (eye cataracts at birth) 0.71 1.02 5.3% Coloboma of eye
(eye parts missing) 0.21 0.40 9.6% Aniridia (absence of the iris) 0.07
0.10 5.2% . HEART Common truncus . (undeveloped main arteries)9 0.19
0.40 11.2% Transposition of great arteries . (reversal of main
arteries) 0.87 1.45 7.6% Tetralogy of Fallot . (4 common defects
simultaneously) 0.73 1.82 13.9% Ventricular septal defect . (opening
between lower chambers) 11.34 20.49 8.8% Atrial septal defect .
(opening between upper chambers) 1.16 3.69 18.0% Endocardial cushion
defect 0.34 0.95 15.8% Pulmonary valve atresia and stenosis .
(obstructed blood flow) 0.58 3.44 29.0% Tricuspid valve atresia and
stenosis . (obstructed blood flow) 0.16 0.36 12.3% Aortic valve
stenosis and atresia . (obstructed blood flow) 0.22 0.79 20.0%
Hypoplastic left heart syndrome . (undeveloped left side) 0.56 1.25
12.2% Patent ductus arteriosus . (pulmonary artery open to aorta) 17.87
35.43 10.3% Coarctation of aorta . (constriction of the aorta) 0.74
1.15 6.5% Pulmonary artery anomaly 1.12 2.66 13.2% Lung agenesis and
hypoplasia . (undeveloped lungs) 1.66 3.84 12.7% . FACIAL CLEFTS Cleft
palate without cleft lip 5.05 5.33 0.8% Cleft lip 7.76 9.35 2.7% .
GASTROINTESTINAL Tracheoesophageal anomalies . (upper airway problems)
1.86 2.49 4.3% Rectal and intestinal atresia . (blockage) 3.23 3.80
2.3% . GENITOURINARY Renal agenesis and hypoplasia . (one kidney or
small kidneys) 1.23 2.34 9.6% Bladder exstrophy . (gap in abdomen, .
revealing bladder) 0.29 0.33 1.9% . MUSCULOSKELETAL Reduction
deformity, upper limbs . (arms deformed or missing) 1.53 1.58 0.5%
Reduction deformity, lower limbs . (legs deformed or missing) 0.78 0.83
0.9% Congenital arthrogryposis . (contracted or bent limbs) 1.33 1.93
5.5% . =========== Source: Larry D. Edmonds and others, "Temporal
Trends in the Prevalence of Congenital Malformations at Birth Based on
the Birth Defects Monitoring Program, United States, 1979-1987,"
39, No. SS-4 (December, 1990), pg. 22.

Descriptor terms: birth defects monitoring program; cdc; new england
journal of medicine; norway; hydrocephalus; encephalocele;
microcephalus; anophthalmos; congenital cataract; coloboma of the eye;
aniridia; common truncus; heart; head; brain; tetralogy of fallot;
ventricular septal defect; atrial septal defect; endocardial cushion
defect; pulmonary valve atresia and stenosis; tricuspid valve atresia
and stenosis; aortic valve stenosis and atresia; hypoplastic left heart
syndrome; patent ductus arteriosus; coarctation of aorta; pulmonary
artery anomaly; lung agenesis and hypoplasia; cleft palate;
tracheoesophageal anomalies; rectal and intestinal atresia; renal
agenesis and hypoplasia; reduction deformity; congenital

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