A FOLLOW-UP
STUDY
OF
CHILDREN
OF
LOW
BIRTH
WEIGHT
AND
CONTROL
CHILDREN
AT
SCHOOL
AGE
Nancy M. Robinson, Ph.D., and Halbert B. Robinson, Ph.D.
Department of Psychology, University of North Carolina, Chapel Hill
(Submitted July 27; accepted for publication September30, 1964.)
This study was made possible by grants from U.S. Children’s Bureau and North Carolina State Board
of Health, and by the generous co-operation of the Wake County Department of Health.
ADDRESS: Department of Psychology, University of North Carolina, Chapel Hill.
425
PEnjAmics, March 1965
T
hERE APPEARS to be relatively littleagreement as to whether low birth
weight (or prematurity) itself carries any
particular risk to the child. As more and
more evidence has accumulated, low birth
weight has come to be seen as only one
variable which is involved in a tangled
web of etiology. It is associated with poor
SOC1OCCOI1OH1iC status; with maternal age,
health, and medical care; and with a
num-l)er of complications of pregnancy which
may hep to bring about the low birth
weight or which themselves may be caused
l)V the same set of circumstances as is the
preiliature birth. The “pure” case of low
birth weight in an infant born to a healthy,
young middle-class mother whose
preg-nancy and delivery are both
uncompli-cated is a rather uncommon event.
Some of the controversy about the effects
of low birth weight stems, too, from the
nature of most of the early research, which
tended to employ biased samples, naive
research design, and poor or non-existent
control groups.1 There was, also, among
the earlier studies, imperfect agreement as to the definition of prematurity, although
the usual criterion has now come to be a
birth weight of 2,500 gm or less. Ideally,
both birth weight and gestational age
are taken into account in defining
pre-maturity since there is some evidence that
low birth weight at or near term is
asso-ciated with greater handicap than is low
birth weight at 36 weeks or less.3
Informa-tion as to gestational age is often
unavaila-l)le, and estimates made by mother or
physician tend to be notoriously
unrelia-ble. Probably the most serious fault in
studies of very small infants has been the
failure to take into account the
socioeco-nomic status of families. It is well known
that both intelligence and birth weight are
highly related to social status, and a finding
of low intelligence in a group of small
in-fants may thus reflect family background
as thoroughly as it does the low birth
weight.
On the basis of a comprehensive review
of recent studies of the psychological
cor-relates of low birth weight, it seems
pru-dent to conclude that a birth weight
be-tween 3 lb (1.3 kg) and 53 lb (2.4 kg) carries
hut a small increase, if any, in the risk of
neurological deficit, mental retardation,
personal or social maladjustment, if other
background variables are taken into
ac-count.
Interest of late has centered in children
whose birth weights were under 1,500 gm,
because the incidence of defects of many
kinds has been found to be high in this
group. Striking improvement in the
sur-vival rates of these very small infants has
occurred within the last few years. The
majority of infants over 1,500 gm can now
be expected to survive, as can even a
siza-ble minority of those under 1,500 gm. One
worker whose central interest has been
the study of very small infants is Cecil
Mary Drillien,5#{176} whose longitudinal studies
have demonstrated striking incidences of
physical and mental handicaps in children
who had weighed 3 lb or less at birth. In
one of her studies,8 for example, one-half
in-LOW BIRTH WEIGHT CHILDREN
educable in normal schools for reason of
physical or mental handicaps or both;
one-quarter were so mentally retarded as to
require special educational treatment in
regular schools; and the final quarter were
considered of low average intelligence or
better. The incidences of abnormalities
re-ported by Drillien have tended to be
higher than those of other researchers,
al-though her general conclusion of a much
increased risk in very small infants has
been repeatedly upheld.bOhi
Many authors, moreover, have reported
that premature children show an unusually
high number of nervous symptoms and
be-havior problems.1 1316 The behavior
prob-lems have been variably attributed to brain
injury, to complications of pregnancy and
delivery associated with low birth weight,
to maternal age, to socioeconomic factors,
to the isolated or stimulus-deprived nature
of life in the incubator, to the mother’s
dis-tress at the emergency atmosphere
sur-rounding premature delivery and
separa-tion from her baby, and to later
overprotec-tion by anxious parents.
The multiplicity of these theories
con-firms the notion that low birth weight must
be considered in context, as but one
varia-ble in a matrix of interrelated adverse
con-ditions which cause, accompany, and
fol-low early delivery. Research which is
aimed at discovering the independent roles
of these variables is necessary before we
can conclude that low birth weight itself
is an important cause of physical ill-health,
mental retardation, or personality
dis-orders.
PLAN OF THE STUDY
The present study constitutes a
compre-hensive follow-up of a group of premature
and mature infants born in Wake County,
North Carolina, during the period
Octo-ber 1, 1948, to October 31, 1951. The study
was initiated in 1959 in connection with
a program of neonatal hospital care for
infants of low birth weight.17 The program
had been carried out by the North
Caro-lina State Board of Health, with the
finan-cia! support of the Children’s Bureau of
the Department of Health, Education, and
Welfare.#{176} The study was originally
planned as a follow-up of infants who had
been cared for on the program. In order
to provide objectivity in this investigation,
it was decided to study, in addition,
corn-parable characteristics of two matched
con-trol groups: (1) children whose birth
weights had been low but who had not
been cared for on the program, and (2)
children of mature birth weights.
Following the completion of this study,
in the manner to be described below, it
was decided to expand the analysis of the
data in order to explore a number of
ques-tions related to the characteristics of
chil-dren whose birth weights had been low.
Specifically, an attempt was made to
evalu-ate the status of these children while at
the same time taking into acount a
nurn-ben of important background variables. In
other words, the general question toward
which this further analysis was oriented
was the following: What is the general
prognosis of a child whose birth weight
was 2,500 gm or less, compared with a
child of comparable social background
whose birth weight was over 2,500 gm?
In this analysis, special attention was also
given to children with birth weights under
1,500 gm, and to those who had sustained
no major physical defects which would
0
The following persons played major roles in initiating the research and in carrying it through the phase of data collection : James R. Abernathy,Katherine Barrier, A.C.S.W., Sidney Chipman,
M.D., James Donnelly, M.D., A. H. Elliott, M.D.,
Isa C. Grant, M.D., Bernice Guthrie, MA., Eileen
Kieman, RN., Ralph McGill, Ph.D., Ellen J.
Preston, M.D., James Rhyne, M.D., Frances E.
Sellers, RN., Rebecca Swindell, RN., Flora
Wake-field, R.N., Bradley Wells, Ph.D., and Charles
Williams, M.D. The present authors became
in-volved with the study only during its second
phase. Valuable assistance was rendered to them
during the analysis of the data by Sidney
Chip-man, M.D., Elaine Jarman, MA., Ellen Kaplan,
Ann Peters, M.D., Theodore Scurletis, M.D., Lotte Strupp, and Bradley Wells, Ph.D. The contribu. tions of each individual are acknowledged with
TABLE I
MORTALITY OF SAMPLES
death certfficates
ing since birth.
for the period
interven-It was discovered that
seriously affect the prognosis for their
de-veloprnent.#{176}
Samples
Each of the original group of 141
chil-dren who had been cared for on the
pre-mature program was matched, via birth
certificates, with two comparable children,
one of whom had been of low birth weight
but who had not been cared for on the
program, and one of whom had not been
of low birth weight. All birth certificates
in the county for the period in question
were stratified by the following categories:
(1) single or multiple birth, (2) birth
weight by 500-gm intervals (low birth
weight only), (3) race, (4) sex, (5) place of
birth, (6) father’s occupation, (7) marital
status of mother, (8) age of mother, (9)
parity, and (10) attendant at birth. Two
matching cases for each of the original
low birth weight group were selected
ran-domly from the matching
cross-classifica-tions generated by the foregoing ten
cate-gories, in that order of priority. One case
was matched for birth weight as well as
each of the other variables, while for the
second matching all the variables
exclud-ing birth weight were employed.
Despite this care in matching, one
im-portant feature, survival, was unavailable
on the birth certificates. Survival
informa-tion was later obtained by matching birth
certificates for the three samples with the
0 Exclusion of the children who had sustained
major physical defects rested on two main grounds: (1) A major goal of the study was the refinement of
prognostic statements about infants of low birth
weight who have survived the first few months of life. When gross physical abnormalities are ap-parent, prognosis must of course depend primarily
upon the defect. Major questions remain, however,
concerning expectations about the development of other children of low birth weight. (2) Retention
of these children in the analyses would have
pro-duced statistically significant but spurious group
differences in almost every comparison, because of
the grossly deviant height, weight, head size, IQ,
and behavior of the damaged children. Such
statistical tests would have revealed little or nothing about the large majority of the children who had sustained no such damage.
Premalures
On Off
Program Program
Malure8
Total 1)ead
One day or less
‘2-6 days 7-27 days
28 days-Il 1110
More than one year
Survivors
141 4
7
3
2
9
3
117
14!
6
40
11
2
7
2
79
141
6
1
0
0
5
0
135
there had been a particularly low death
rate in the first few days of life among the
on-program prematures, since these infants
had to survive long enough to be
trans-ferred to the program, usually a matter of
24-48 hours. Table I shows the mortality
characteristics of the three groups.
Data Collection
Extensive data were collected on each
case studied. The over-all plan was as
fol-lows : Initially, each family which could
be located was visited by a public health
nurse and invited to participate in the
study; second, the family was visited and
interviewed by a trained social worker;
third, the child was given a thorough
physi-cal examination at the county health
de-partment by pediatric and laboratory
per-sonnel; and finally, testing was carried out
by a trained psychologist. With the
excep-tion of the public health nurse, all those
who saw the child or his family were kept
ignorant of his birth weight.
The public health nurse was originally
responsible for locating the families and
securing their co-operation. Of the
surviv-ing children, there were no significant
dif-ferences between the three samples in the
proportion who became participants in the
study. Sixty-eight percent of the surviving
on-program and mature samples
respectively), and 70% (55) of the
off-pro-gram survivors became participants. The
majority of those not participating could
not be located by the nurses.
The nurses also made exhaustive
at-tempts to search hospital records
concern-ing delivery and neonatal status, records
of attending obstetricians, and subsequent
pediatric records for the children.
Unfor-tunately, so many of these data were
unavailable or inadequate that they could
not be included in the present analysis.
The only data analyzed, therefore, were
those gathered directly from the families
and children at the time of follow-up.
A most serious loss to the study from
the inadequacy of these records was
in-formation related to gestational age at
birth. Such information is ordinarily listed
on birth certificates in North Carolina, but
that information is considered neither
re-fined nor reliable enough for use in the
present study. Reports by the mothers
when the children were of school age were
expected to be even less reliable.
A trained social worker visited each
home and conducted extensive structured
interviews with each mother or foster
mother concerning the social and
eco-nomic characteristics of the home; parents’
educational attainment; attitudes toward
the subject and toward his siblings;
atti-tudes toward child rearing, medical care,
and educational goals for the children;
marital relationships; and emotional
sta-bihity. Reports of the learning ability,
health, and behavior problems of the
sub-ject and siblings were secured. Finally, the
environment was assessed in terms of its
opportunity for social contacts and for
mental stimulation.
Each child was given a thorough
pediat-nc examination, including evaluation of
ophthalmologic and neurologic status and
of visual and auditory acuity. Routine
lab-oratory screening by a registered
techni-cian included hemoglobin determination,
white blood cell count and differential,
sickle cell preparation, urinalysis, tests for
phenylketonuria and syphilis. Special
con-sultations were carried out as indicated.
A trained psychologist tested each child
by means of the 1937 Sandford Binet, Form
L; the Coodenough Draw-a-Man Test; the
Jastak \\Tide-Range Achievement Test
(Reading); and special behavior rating
scales. Records of grade placement and
school attendance were obtained, together
with behavior ratings from the child’s
cur-rent teacher.
Analysis of the Data
Because of obvious differences in the
mortality of the three original samples,
and because the main concern of the
pres-ent study was in the relationship of birth
weight to the development of the children,
the original groups were reconstituted
ac-cording to birth weight. Group I consisted,
as before, of the 92 mature control
sub-jects. The 135 low birth weight subjects,
80 of whom had been cared for on the
pro-gram and 55 of whom had not, were
di-vided into two groups : Group II,
consist-ing of the 102 children with birth weights
between 1,500 and 2,500 gm, and Group
III, consisting of the 33 children with birth
weights of 1,500 gm or less. As a second
step, those subjects who had sustained
ma-jor physical defects were excluded from
each group. Most of the analyses to be
reported were carried out on the three
groups defined according to birth weight,
but excluding those who had sustained
major physical defects.
The three groups, thus defined, were
corn-pared statistically on each of the more
than two hundred variables measured. For
measures which afforded a continuous
range of values (e.g., weight, height, head
size, IQ, behavior ratings), special
least-squares analysis of variance and covariance
proceduresls were possible. These
proce-dures, carried out by means of a UNIVAC
computer, permitted sensitive group
corn-parisons on each variable while at the
same time controlling for a number of
#{176}Copies of the behavior rating scales may be
TABLE II
DEscuIvrIoN OF SAMPLES
Variable Group I More than 2,500 gin II 1,501-2,500 gum III 1,500 gut ar Less Total Signif. of D(ff. Original participants
Number with major (lefect
Remaining sample Race White Negro Sex Male Female Social class* 1-3 4 5
Age of child (months)
Mothers educationt Father’s educationt 92 ‘2 90 45 45 47 43 21 28 41 108.8 3.6 3.2 102 3 99 .59 40 50 49 36 21 42 106.0 4.2 3.8 33 8 ‘2.5 9 16 10 15 ‘2 17 16 102.0 3.2 2.8 227 13 214 113 101 107 107 59 56 99J 106.7 3.9 3.4 < .001 .05 .05 .05
* Warner Index of Social Characteristics.
t Coded as follows: (‘2) below 7th grade, (3) 7-9grades, (4)some high school.
other relevant variables (e.g., race, sex,
age, social class, mother’s education). The
use of these procedures may constitute a
unique contribution of this study to the
literature on the effects of low birth
weight.
RESULTS
Description of Samples
Data concerning some variables
describ-ing each of the three birth-weight groups
are presented in Table II. Chi-square and
analysis-of-variance techniques applied to
these data indicated significant differences
in the proportion sustaining major physical
defects, the social class of the families, the
age of the child, and tile mother’s
educa-tion. It should be noted that, although
originally the low birth weight sample as
a whole was closely comparable to the
ma-ture control group, the smallest babies
tended to be born to relatively
disad-vantaged families, while the Group II
babies came from homes higher on the
socioeconomic scale. Had the original
groups not been matched, however, there
is no reason to suppose that the Group II
sample would have come from superior
socioeconomic circumstances. It should
al-so be noted that the original selection
pro-cedure, which was based on a sample of
children who had been cared for on a
pub-lie program, insured that a high
propor-tion of families of low socioeconomic status
would be included in the total sample.
The age differences between the groups
cannot be readily explained and probably
represent a chance variation.
Subjects with Major Defects
Children who were found to have
sus-tamed a major physical defect, congenital
or acquired, were eliminated from further
consideration. Low mental ability did not,
in the absence of major physiological
ab-normalities, constitute a basis for
exclu-sion. The seriousness of the defect was
judged by the examining physician and
was subject to review by other research
LOW BIRTH WEIGHT CHILDREN
* “Severe deficiency.”
occurred in the sample of Group III
chil-dren and constituted 24% of that group,
compared with incidences of only 2% and
3% of Groups I and II, respectively.
Char-acteristics of these children are shown in
Table III. It should be noted that
retro-lental fibroplasia accounted for the defect
in two of the children, both with birth
weights of 1,500 gm or less. A third child
with this disorder also exhibited
ques-tionable cerebral palsy.
Computer Analysis
For those variables which yielded a
con-tinuous distribution of measurement, it
was possible to utilize sensitive statistical
procedures to investigate the role of
pre-maturity independent of such related
fac-tors as sex, race, social class, and mother’s
education. The three birth-weight groups
were compared on each continuous
vari-able, the covariance of background
vari-ables being taken simultaneously into
ac-count. For a few variables, principally the
teachers’ ratings of school behavior, a few
values were unavailable for some subjects.
The total sample thus ranged in number
from 198 to 212 for the separate analyses,
most analyses, however, being carried out
on 208-212 subjects. Group III was then
compared with Groups I and II on each
variable in which the over-all analysis was
statistically significant. Because ten
over-all comparisons had originally been carried
out, this procedure tended to capitalize on
any chance differences obtained. The
re-sults of these analyses are shown in Table
IV. In Table IV is also shown the parallel
analysis of covariance for subjects grouped
according to social class rather than to
birth weight.
Analysis of Non-continuous Variables
A total of approximately 200 other
sep-arate comparisons of the three groups was
made, most of the comparisons dealing
with the gross presence or absence of
spe-cific signs of abnormality. No statistical
control procedures for background
van-ables were possible with these data.
Accord-ing to chance alone, approximately ten
comparisons would be expected to reach
the .05 level of significance, and two would
be expecteed to reach the .01 level. In fact,
a total of eight comparisons were found to
be significant at the .05 level or better, five
TABLE III
CHARACrERISTICS OF CHILDREN WIT!! MAJOR DEFECTS
Group Race Sex JQ Defect
I ‘V M 5 91 Impaired vision, club foot
I W ii: 4 84 Impaired hearing (chronic otitis media)
II \V F 3 86 Bilateral congenital deafness (both sibs also deaf)
II %V M 3 127 Congenital heart defect; congenital severe
de-formity of hands and arms
H N F 5 <30 Microcephalic (48.0 cm)
III W F ‘2 87 Blind (retrolental fibroplasia); co-ordination oor
III W M 3 82 Blind (retrolental fibroplasia)
III W M 3 23 Microcephalic (48.2 cm) ; mute; cerebral palsied
III W F 3 98 Blind (retrolental fibroplasia)
III W F 5 74 Microcephalic (48.0 cm) ; impaired vision (left
eye)
III N M 5 * Microcephalic (45.5 cm); cerebral palsied;
ques-tionable vision
III N M 4 20 Mongoloid
III N F 5 57 Mental deficiency (etiol. unknown) with neurol.
Dependeni
Variable
Group 1
i%!
U
Group II
M
g
Group ill Al
Total M
q
Significance of Analy8es
All
Groups I-If
Social
Class
Ileight 52.82 51.59 50.48 51.97 <.10 <.10 u.s. <.05
(in.) 3.15 3.47 2.66 3.34
Weight 64.6! 59.42 55.44 61.11 <.05 <.05 u.s. .05
(lb) 12.64 10.85 9.35 11.87
ileadsize 51.97 51.32 50.64 51.51 <.01 <.01 u.s. .01
(cm) 1.54 1.58 1.’2 1.58
Stanford- 86.24 88.03 79.54 86.32 n.s. <.001
Billet IQ* 17.78 17.68 16.06 17.65
Goodenough 8.5.97 90.00 85.12 87.77 na. .05
IQ 19.08 18.73 15.63 18.60
Jastak 29.30 30.52 ‘23.12 ‘29.16 u.s. <.01
Score 11.87 14.15 10.32 12.98
Test Behav. .58 .65 .71 .63 n.s. n.s.
It .73 .90 .86 .82
TestBehav. 12.00 12.16 12.65 12.14 u.s. <.001
hf ‘2.46 2.39 1.67 ‘2.35
School ‘2.52 2.09 3.30 2.41 11.5. n.s.
behaviort 2.39 2.49 2.79 2.50
Adversesocial ‘2.29 1.96 2.64 2.18 u.s. .001
factors ‘2.06 1.85 ‘2.10 1.97
* 1937 Stanford-Binet, Form L, calculated by 1960 tables for Deviation IQ.
tSpecial behavior rating scales. In each instance, a higher value represents a more negative appraisal.
Measure of adverse social factors or events (e.g. death of parent, submarginal economic status) in home since
birth. A higher value represents a more adverse condition.
TABLE IV
GROUP MEANS AND STANDARD DEVIATIONS USED IN COMPUTER
ANALYSES OF CONTINUOUS VARIABLES
of these reaching the .01 level. These few
differences would be expected on the basis
of chance alone, but they do, in general,
appear to fit the pattern of social class
differences already substantiated by the
analyses shown in Table IV. The
chi-square analyses reaching the .05 level or
better are listed in Table V.
COMMENT
The statistical analyses of tile data
gathered in this extensive investigation of
214 children indicate that we should be
extremely cautious in attributing physical,
intellectual, or personality handicaps to
children of low birth weight who have not
sustained major physical defects. Except
for the findings related to weight and head
size, the data fail to suggest that the two
groups of low birth weight children fared
any less well than might have been
ex-pected from a knowledge of their social
background.
The analyses shown in Table II do
re-veal that, for infants weighing 1,500 gm
TABLE V
EIGHT Co I-SQUAll E ANALYSES RE.wIIING THE
.05 LFvF:t OF SIGNIFICANCE
Iariab!e
Physical examination
I. ‘rNth carious; 3 or more
. One or more teeth
filled
Scial history. interview
S. Child lives with other
than his parents
4. Family received help
from social agencies
3. Mother seeks nochild
care information
Teacher behavior ratings(19)
6. Poor relations with
other children
7. Aggressive
8. Impulsive
Psychological testing
None
Group
II
N=99
(c7c)
4 38
S
30
4
9
8
.v=o (o)
Si
34
35
7
14
8
“I N =5’
(%)
68
8
28
64
55
22
30
17
defect of major proportions was
signifi-cantly greater than that of the mature
controls, but there was no increased risk
among the group which weighed more
than 1,500 gm at birth. There was,
more-over, a significant difference among the
groups on variables related to
socioeco-nomic class and education, particularly the
education of the mother. The data indicate
that the social class of Group III families
was significantly lower than that of Group
II, suggesting that any evaluation of the
subsequent development of tiny prematures
must take into account this important
back-ground variable.
The analyses shown in Table IV indicate
that, for these several measures, only those
having to do with physical size are related
to the child’s birth weight, when other
background factors are held constant.
Fur-thermore, even the measures of physical
size do not differentiate between Groups
II and III, though these two groups are
different from the normal controls. The
data thus suggest, not surprisingly, that
children of low birth weight will, on the
average, remain smaller than children of
normal weight at birth. The data suggest,
however, that when other factors are taken
into account, low birth weight is not
necessarily a precursor of low intelligence,
imnaired reading ability or over-all
meas-J,tneI
01 ures of behavioral inadequacy, unl?ss the
S*gnzf. child sustains a major physical defect.
The analysis shown in Table I\
accord-ing to social class, however, underscores
.01 the importance of that variable as it
re-.01 fleets the complex of adverse results which
have often been attributed to low birth
.01 weight. Measures of intelligence, reading
ability, and behavior, as well as measures
.01 of body size, were all significantly related
.05 to social class. Since social class is
signifi-cantly associated not only with the
mci-.OQ dence of low birth weight, but with its
:
degree, it is, thus, extremely important totake this variable into account when
assess-ing prognosis.
The analyses shown in Table V must be
evaluated with extreme caution, since they
contain no correction for the significant
social-class differences among the three
groups, and since their number does not
exceed that expected by chance. The few
significant differences are, as a matter of
fact, probably more closely related to social
class than to birth weight. If any area
covered by the evaluation deserves
follow-up, it may be the social behavior of the
children. The ratings given by the
psychol-ogist on the basis of a brief sample of
be-havior failed to reveal differences among
the groups, but the teachers tended to see
the Group III subjects as somewhat more
impulsive, aggressive, and distractible, and
to have somewhat poorer relationships with
other children. While this pattern may well
be related to social class, it should also be
noted that these qualities of behavior are
precisely those described
by
AlfredStrauss19 as being indicative of brain
dam-age in children. In view, however, of the
paucity of significant differences among
the groups, it would not be surprising if
this finding were not repeatable with
ARTICLES 433
SUMMARY
A comprehensive follow-up of survivors
of matched groups of low- and
mature-birth-weight infants born in \Vake County,
North Carolina, was carried out when the
children were approximately 8 to 10 years
old. The sample included 92 who had
weighed more than 2,500 gm at birth, 102
with birth weights of 1.501-2,500 gm, and
33 who had weighed 1,500 grn or less.
Covariance techniques were utilized to
hold background factors constant in some
of the analyses. A higher proportion of the
tiniest infants had sustained major physical
defects (24% vs. 2-3% in other groups). This
group was significantly smaller in weight
and head size, and tended to come from
more disadvantaged socioeconomic
back-grounds. Extensive comparisons of data
from physical and psychological
examina-tions, social histories, and school reports
tended to find only a few significant
differ-ences among the groups, all of which were
probably related more closely to social
background than to birth weight per se.
The data indicate that, aside from physical
size and major physical defects, social class
assumes much more importance than does
birth weight in determining a child’s
de-velopmental prognosis.
REFERENCES
1. Benton, A. L. : Mental development of
pre-maturely born children. Amer. J.
Ortho-psychiat., 10:719, 1940.
2. WHO Technical Reports Series No. 217.
Public Health Aspects of Low Birth Weight. Geneva: World Health Organization, 1961. 3. Baird, D. The contribution of obstetrical
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