OUTCOME,
WITH
SPECIAL
REFERENCE
TO
HIGH
BIRTH
WEIGHT-LOW
GESTATIONAL
AGE
INFANT
Frederick C. Battaglia, M.D., Todd M. Frazier, ScM.,
and Andre E. Hellegers, M.D.
Departments of Pediatrics and Grjnecology-Obstetrics, The Johns Hopkins University and Hospital, Baltimore, Maryland, and the District of Columbia Department of Public Health
(Submited July 14; accepted for publication August 12, 1965.)
PRESENT ADDRESS: (F.C.B.) University of Colorado Medical Center, 4200 East 9th Avenue, Denver, Colorado 80220.
A.E.II. is Senior Research Scholar, Joseph P. Kennedy, Jr., Memorial Foundation.
PEDIATRICS, Vol. 37, No. 3, March 1968
417
r-I-,
HROUGH the years there has beendis-.1. agreement on the optimum way of
assessing prematurity in products of
con-ception. To the layman, the premature
baby is the one born too soon. Along these
lines, the World Health Organization has
recommended that babies of birth weight
less than 2,500 gm be called “low birth
weight” infants with the implication that
prematurity could better be defined by a
gestational age of less than 37 weeks.1 One
of these is patient bias in reporting the first
day of the last menstrual period.2 In
addi-tion, it is known that approximately 20% of
all pregnant women have spotting or
bleeding of various degrees in the first
twenty weeks of pregnancy. Such periods
of bleeding may be interpreted as normal
or near normal menstrual periods and
du-ration of the gestation calculated on the
basis of such a bleeding episode. On the
assumption that such confusion would be
avoided by the use of infant weights, the
standard definition of prematurity as an
in-fant weighing less than 2,500 gm was
adopted.3 However, recently a variety of
terms have been used to describe the
in-fants in whom a discrepancy between
weight and gestational age has been in
whole, or in part, the basis for the clinical
syndrome (e.g., intrauterine growth
retar-dation, dysmaturity, postmaturity,
placen-tal insufficiency syndrome, low
birth-weight infants, etc.) For this reason it has
been recommended that gestational age be
used as the better indicator of fetal
out-come. It should be noted that this return to
the older definition is based on the
exis-tence of infants, who while premature by
weight, are really mature in terms of organ
development.
If each of the classifications has its value,
it would seem sensible to investigate
whether the combination of weight and
gestational age does not offer predictability
of outcome more exact than either of its
components taken alone. It is the purpose
of this study to investigate this hypothesis.
METHOD
All consecutive single-born deliveries of
20 weeks or more gestational age occurring
in Baltimore City during the years 1959,
1960, 1961 are presented. The data were
obtained from birth certificates filed with
the Baltimore City Department of Health.
The data were sorted into groups
pertain-ing to white and non-white patients. No
data were discarded except those in which
no information had been given as to
gesta-tional age. In all cases the gestational age
was estimated from the first day of the last
menstrual period. For inclusion of data by
2-week-age groups the following example
was followed throughout: Gestational ages
of 29 weeks and 4 days were counted as 30
weeks; those of 31 weeks and 3 days as 31
weeks. Consequently the midpoint of the
stated interval 30-31 weeks is 30 weeks
and 4 days. A total of 68,343 cases were
re-viewed, 35,706 white and 32,637 non-white
J’-.
3200
2800
-2400
2000
1600
t200
800-400
#{149}Baltimore City
ONew York City #{149}Denver
25 27 29 31 33 35 37 39 41 43
Week of Gestation
Fic. 3.
Fic. 1.
RESULTS
Birth Weight and Gestational Age Groups
The Baltimore data are presented in
Fig-ure 1. It is evident that the frequency
dis-tribution of infant birth weights at any
given gestational age is not represented by
a sharply delineated peak but rather by a
BIRTHWEIGHT PERCENTILES AND GESTATIONAL AGES
SINGLE BIRTHS
Weight NEW YORK CITY AND BALTIMORE
gm.
NEW YORK CITY, BALTIMORE CITY
AND DENVER
Aeight
gms
4000
3600
3200
2800
2400
2000
600
I 200
800
400
25
W..k of G.station
FIG. 2.
#{149}Boltimore City
ONew York City
UDenver
27 29 31 33 35 37 39 41
Week of Gestation
Fic. 4.
COMPARISON OF MEDIAN (50th PERCENTILE LEVEL)
FOR
Weight
gnu NEW YORK CITYBALTIMORE CITY AND DENVER
4000
-3600
varying series of curves. As expected,
skew-ness is most evident in the distribution in
early gestational age groups, with the more
uniform and tight distribution occurring
closer to term. This figure is the
compli-ment of Figure 1, in the study by Erhardt
et al.1 which presented the frequency
000- #{149}MORTALITY RATES BY WEIGHT
10
--PMR Baltimore
0- -o NMR Baltimore -. PMR NewYork 0-C NMR New York
a-#{149} PMR Baltimore --O NMR Baltimore
-PMR New York
-o NMR New York
400 200 2000 2800 3600 4400 5200
Fic. 5.
tribution of infants by duration of
pregnan-cy for specific birth-weight groups. Their
study based on 671,915 births in New York
City is comparable in methodology to the
present study. Together the two figures
provide a complete description of the
fre-quency distribution of infants by weight
and by gestational age. To what extent the
wide distribution at early gestational ages
in the present study is due to errors in the
estimation of pregnancy duration as
calcu-lated from the last menstrual period or due
to true biologic variability cannot be
decid-ed from these data alone.
The percentile curves for the distribution
‘00-
,0-1000 MORTALITY RATES BY GESTATIONAL AGE
too
121 25 29 33 37 41 45 49
FIG. 6.
of all white infants by weight and
gesta-tional age are presented in Figure 2.
Fig-ure 2 presents the data for Baltimore City
and New York City (the latter data
calculat-ed from the study of Erhardt et al.).4 The
striking agreement between the Baltimore
and New York data totaling 548,903
de-liveries is impressive. Both Figure 1 and
Figure 2 clearly illustrate the greater
spread of infant weights at early
gestation-a! ages than at term in the Baltimore and
New York data.
Figures 3 and 4 present the median
weight distribution (i.e., the 50th percentile
curve) and the 90th percentile curves
re-spectively for the Baltimore and New York
and for the Denver data of Lubchenco, et
TABLE I
PERINATAL MORTALITY RATES FOR SINGLE DELIVERIES BY BIRTH VE1GHT, BY DURATION OF PREGNANCY
FOR WHITE INFANTS
Duration of Pregnaniy (Weeks)
Birth Weiyht (U
)
Under 1,001 1,001-1,500 I 501-2,000 2,001-2,500 2,501-3,000 3,001-3,500 3,501-4,000 4,001-4,500 4,501-5,000 5,001-and over Total 20-23 989.6 750.0 445.8 338.5 128.2 61.0 45.5 0.0 0 600.0 861.9 _#{176}6-27 936.5 7.56.4 338.7 123.3 36.6 47.2 179.5 0 0 0 654.4 28-29 899.5 612.7 445.7 181.8 50.9 45.2 14.5 111.1 0 0 466.3 30 921.1 503.3 431.6 150.0 50.4 16.3 30.3 0 0 0 302.4 31 955.8 545.0 366.5 175.4 54.7 24.2 26.1 69.0 0 .500.0 252. 1 32 988.9 583.3 273.9 186.7 54.2 33. 1 6.5 29.4 166.7 1000.0 191.1 944.4 668.6 245.4 117.4 45.2 21.4 22.5 0 166.7 0 129.6 34 986.1 612.4 247.0 86.2 37.4 18.8 22.5 69.0 142.9 0 85.1 930.2 648.6 249.0 74.4 35.6 15.3 24.6 27.2 174.0 166.7 58.9 56 970.6 580.4 236.2 62.2 24.4 13.8 17.! 34.6 63.8 76.9 39.0 37-39 860.5 641. 1 226.0 44.5 10.9 6.3 6.5 13.2 45.9 131.! 12.5 40 and O’er 761 .2 540.5 290.9 54.3 14.4 7.6 7.4 9. 1 15.2 78.3 11.1 Total 958.7 623.6 284.2 63.5 14.9 7.6 7.6 10.9 23.4 98.7 25.8NEONATAL MORTALITY RATES FOR SiNGLE LIVE BIRTHS BY BHIT1I WEIGHT, BY DURATION OF PREGNANCY FOR WHITE INFANTS
Duration of Pregnaney (Wee(s) Birth Weight
(gm)
Under 1,00! 1, 001-1, 500
1,501-2,000 2,001-2,500 2, 501-3, 000 3,001-3,500 3,501-4,000
4,001-4, 500 4, 501-5, 000
5,001-and over Total Under 20 993.7 500.0 571.4 166.7 0 250.0 0 0 0 0 792.8 20-25 977.5 650.3 303.0 156.9 116.9 37.5 45.5 0 0 0 745.2 26-27 899.8 698.4 233.6 58.8 24.7 38.1 157.9 0 0 0 549.8 28-29 794.9 547.7 353.7 104.5 37.6 28.7 14.5 1!!.! 0 0 349.9 30 750.0 379.2 370.4 86.0 27.8 4.1 20.4 0 0 0 191.0 3’ 848.5 445.2 327.1 126.4 31.2 15.2 8.8 35.7 0 500.0 177.0 32 933.3 409.4 205.5 119.9 23.2 23.0 0 0 0 1,000.0 112.2 33 733.3 456.3 173.1 86.3 19.3 8.0 7.6 0 0 0 70.9 34 923. 1 390.2 152.8 59.8 20.5 10.1 11.4 24.1 0 0 44.5 35 666.7 339.2 107.4 39.2 22.2 9.0 10.2 16.5 95.2 166.7 27.! 36 875.0 318.8 103.6 31.1 12.2 5.6 6.7 18.9 22.2 0 16.9 37-39 586.2 364.4 118.8 22.2 5.9 3.5 3.1 6.4 11.3 27.5 6.1 40 and Orsr 483.9 370.4 154.0 28.1 7.5 3.9 3.9 4.2 3.3 24.1 5.5 Total 916.7 493.5 188.9 35.4 8.0 4.0 3.8 5.1 5.5 31.4 31.4
disagreement at the 50th and 90th
percen-tiles between the Baltimore and New York
data on the one hand and the Denver ones
on the other.
Fetal and Neonatal Mortality Rates
for White Infants
Figures 5 and 6 present the neonatal and
perinata! mortality rates for both the New
York
and
Baltimore data, by infant weightand by gestationa! age respectively.
Com-parable data were not available in the
Denver study. Again, the striking
agree-ment between the New York and Baltimore
data for pregnancy outcome by infant
weight and gestational age is evident in
both figures. In addition we should like to
emphasize an interesting feature of Figure
6, namely, that for every increase of two
weeks in gestational age, the perinatal
mor-tality rate is decreased by approximately
one half. While the figures illustrate the
marked decrease in perinata! mortality
rates with increasing weight or gestational
age, they do not give the death rate for a
given gestational age and weight. For this
purpose Tables I and II giving the New
York perinatal and neonatal mortality rates
are reproduced from the article of Erhardt
et al., since this is the largest single study
available.0 The Baltimore data as shown in
the previous figures are in good agreement
#{176}The authors should like to thank Dr. Carl L.
Erhardt and the American Public Health
Associa-tion for their courtesy in allowing reproduction of
Tables I and II.
with the New York data for both perinatal
and neonatal mortality at any weight and
gestational age. We should particularly like
to call attention to the 2,000 to 2,500 gm
weight group in which there was a marked
decrease in perinatal mortality rate as
ges-tational age increased. This has been
em-phasized previously in the study of Anctel
Ct al.#{176}
COMMENTS
Terms used to describe possible clinical
entities are useful only to the extent that
these entities are precisely defined and thus
the group of patients referred to clearly
de-lineated. It will be noted that substantial
agreement exists between the New
York-Baltimore data and the Colorado
data with respect to the “small infant”
syn-drome. However, the discrepancy between
the median birth weights at each
gestation-al age for the New York-Baltimore studies
and the Colorado study is apparent. It
should be kept in mind that in the
Cobra-do study certain categories of infants were
abritarily omitted from the tabulations on
the basis of diseases such as toxemia,
di-abetes, and erythroblastosis, as were
cer-tain infants who were “clearly of the wrong
gestational age for the weight reported.” In
addition, the Denver percentile curves are
constructed on the basis of data obtained
from two sources: the Colorado General
Hospital and other Colordao hospitals
which transferred babies to the Colorado
General Hospital. Since these latter infants
were transferred on the basis of
prematuri-ty as defined by weight, the occurrence of
large babies at earlier gestational ages is
artifically masked in the percentile curves
as presented. All such infants were
in-cluded in the New York-Baltimore data,
hence it is not surprising that these
percen-tile curves in the lower gestationa! ages
contain relatively many large infants.
From the clinical point of view such
in-fants may be viewed in two different ways:
We should also like to thank Dr. Lula 0
Lub-chenco for her co-operation in making the
com-parison of the Baltimore and Denver data more
meaningful through a clarification of the
differ-encer between the populations reported.
(1) It
can be assumed that they are clearlymature infants, and that an error was made
in the reporting of the gestationab age, or
(2) it may be assumed that the gestational
age reported was correct and the infant is
indeed too barge for the gestationa! age,
and thereby represents the opposite scale
of that entity represented by the dysmature
infant. While neither the acceptance of the
gestational age, nor that of the weight, can
solve the question of whether such a
clini-cal entity really exists, the clinician should
in prudence assume that it does since this
will mean giving special attention to a
group of infants of relatively large birth
weight for gestationa! age, who might
oth-erwise not be treated as a “high risk”
group. That such special attention is called
for can be seen from a comparison of the
perinatal mortality rates for infants of
2,500-3,000 gm birth weight and 28-29
weeks gestational age (perinatal mortality
rate-50.9/1000) vs. that for infants of
2,500-3,000 gm birth weight at 37-39
weeks gestation (perinatal mortality
rate-10.9/1000), an approximate fivefold
difference in pregnancy outcome. In the
New York experience the former group
contributes between 13% to 25% of all
in-fants delivered with an estimated
gesta-tional age of 28-29 weeks.
There are at least two possible
explana-tions for the difference in prognosis
be-tween the infants of 2,500-3,000 grams
de-livered at 28 and 38 weeks of apparent
ges-tational age respectively.
1. The infants are truly too large and
represent a form of pathophysiology
char-acterized by an excessive growth rate.
2. The infants are born 28 weeks after a
bleeding episode during early pregnancy,
interpreted as a menstrual period, and this
episode of bleeding carries with it a poor
infant prognosis regardless of its true
ges-tational age at the time of delivery.
Hence, since either of the foregoing
implies the presence of a pathologic
change, we propose the following clinical
approach:
1.
The
obstetrical decision: Thedeliver such an infant (one seemingly too
large for its gestational age) or whether to
keep it in utero, will follow the safer rule
by adding another criterion of maturity to
the above-mentioned ones, such as the
du-ration of audible fetal heart tonesJ It
fol-lows that considerable importance should
be attached at prenatal visits to
deter-mining precisely when the fetal heart is
first heard. Knowing that this will occur at
approximately the twentieth week, the
ab-sence of fetal heart tones in the nineteenth
week prenatal visit should require the
pa-tient to be brought back weekly thereafter
until the fetal heart is heard. She should
not be allowed to remain unobserved until
the twenty-third week since maturity
deter-mined on the basis of the duration of
pres-ence of a fetal heart is an additional
indica-tor of maturity, better than either
gesta-tional age estimated from the last
men-strual period or a clinical estimate of fetal
weight alone, when an obvious discrepancy
exists between them.
2.
The pediatric decision: If delivery hasalready occurred, then the infant
apparent-ly too large for the gestational age should
be observed as if it were a premature
in-fant of that gestational age rather than
as-suming the gestational age to be incorrect
and judging the maturity by infant weight.
By so doing the pediatrician is using a high
index of suspicion in categorizing these
in-fants in a “high risk” gestational age group
rather than a “low risk” birth-weight group.
This seems prudent since one cannot at this
stage reject the possibility of pathology
early in gestation resulting in the
produc-tion of such infants.
3. Finally, it is interesting that errors in
the estimation of gestational age will tend
to produce much greater distortion of the
higher rather than of the lower percentile
curves, i.e., in larger rather than in smaller
babies. This is because there is an absolute
minimum for birth weight (e.g., zero)
which limits the maximum error in the
lower percentile curves. In addition there is
a practical reporting limit since abortions
are not included in these studies. The effect
of this is shown in the fact that the New
York, Baltimore, and Denver data are in
close agreement for the 10th and 25th
per-centiles. Hence, the diagnosis of babies of
disproportionately low birth weight for a
given gestational age can be made with
reasonable assurance from any of the three
sets of data, or the percentile curves.
SUMMARY
The distribution of birth weights at
var-ious gestational ages are presented for all
single births occurring in Baltimore City in
1959, 1960, and 1961. These data are
pre-sented as pregnancy distributions or
per-centile curves for comparison with data of
several other studies. In general, the
fre-quency distribution of birth weights at any
given gestational age spans a wide weight
range.
The neonatal, fetal, and perinatal
mortal-ity rates for various cell groups are
present-ed. There is striking agreement between
these data and those of a similar study
from New York City. The clinical
implica-tions of these mortality rates and percentile
curves are discussed.
REFERENCES
1. WHO. Technical Report Service, 1961, p. 217.
2. Frazier, T. M.: Error in reported data of last
menstrual period. Amer.
J.
Obstet. Gynec.,77:915, 1959
3. WHO. Manual of International Statistical
Classification of Diseases, Injuries and Causes
of Death, Adopted 1948, Geneva: WHO.
1949.
4. Erhardt, C. L., Joshi, C. B., Nelson, F. C..
Kroll, B. H., and Weiner, L.: Influence of
weight and gestation on perinatal and
neo-natal mortality by ethnic group. Anier. J.
Pub. health, 54:1841, 1964, Copright 1964
by the American Public Health Association,
Inc.
5. Lubchenco, L. 0., Hansman, C., Dressier, M.,
and Boyd, E.: Intrauterine growth as
es-timated from liveborn birth-weight data at
24-42 weeks of gestation. PEDIATRICS, 32:
793, 1963.
6. Anctii, A. 0., Joshi, C. B., Lucas, W. F., Little,
W. A., and Callagan, D. A.: Prematurity, a
more precise approach to identification.
Obstet. Gynec., 24:716, 1964.
7. Hellegers, A. E., and Eastman, N. J.: The
problem of prematurity in gravids with
cesar-can section scars. Amer.
