introduction - HealthNet Nepal

INTRODUCTION
Birth weight is the most sensitive and reliable indicator of health of
the community. It is universally acknowledged that size at birth is an
important indicator of foetal and neonatal health in the context of both
individual and population. Birth weight in particular is strongly associated
with foetal, neonatal and post-neonatal mortality and with infant and child
morbidity1. It is the most important determinant of children’s chance of
survival, healthy growth and development in future 2.
Size at birth reflects
foetal growth. So, it must
otherwise the increase in
confounding of growth and
two factors: duration of gestation and rate of
be considered with respect to gestational age,
size that occurs with age will lead to severe
maturity1.
Growth is defined as an increase in size over time and
documentation of increasing size thus require serial measurements.
During foetal life, serial measurements are feasible only with ultrasound,
but they are not sufficiently valid to serve as a standard for assessing
foetal growth as ultrasound estimation of foetal weight has a high
coefficient of variation. Moreover ultrasound measurement are not truly
anthropometric1.
Body size is obviously proportional to age, not only in the foetus but
throughout childhood until the time of skeletal fusion. Thus an infant’s size
at birth reflects the average growth rate for that infant from conception to
birth, although not necessarily a steady stage, as there may have been
periods of rapid and slow growth. Problems arise when the distribution of
size at birth of different infants born at different gestation ages is used to
make inferences about ‘normal’ foetal growth1.
At the other end of the gestational age spectrum, there is also some
evidence that foetuses, who remain unborn pre-term may not have grown
at the same rate as those born earlier. Foetal size is considered to be one
of the determinants of the onset of labour, and the flattening (or even
negative slope) of some foetal growth curves after 40 or 41 weeks of
gestation may reflect both the slowing of growth due to placental
insufficiency, and the earlier birth of faster-growing foetuses 1.
Deriving
foetal
growth
standards
from
anthropometric
measurements of newborn infants may have less relevance to the first 2024 weeks of gestation, when elective, induced abortions are performed for
indications unrelated to foetal growth (i.e. for reasons other than
chromosomal or other genetic abnormalities of the foetus). The situation
changes, however, when all foetuses are included, since a large number of
births during weeks 20 to 24 are spontaneous and probably related to
factors that do effect foetal growth. From week 24 onwards, however, it
should be kept in mind that foetal growth curves based on
anthropometric, measurements of different newborns born at different
gestation ages may not be valid, particularly pre- and post-term1.
The determinants of foetal growth have been the subject of
considerable research and these differ considerably from the aetiological
determinants of gestational duration. In particular, maternal stature, prepregnancy weight and energy intake during gestation all have important
influences on the rate of foetal growth, but much less, if any effect on the
duration of gestation. Genetic(including racial) and inter-generational
effect also bear primarily on foetal growth. Cigarette smoking effects both
foetal growth and gestational duration, but the effect is considerably
greater on the former. Only a few other determinants such as infections,
maternal cocaine use, and pre-pregnancy and gestational hypertension
(particularly severe pre-eclampsia), also affect both outcomes1.
Impairments in foetal growth can have adverse consequences in
infancy and childhood in terms of mortality, morbidity, growth and
performance. It has even been suggested that restriction of foetal growth
may increase the risk of ischaemic heart disease, hypertension,
obstructive lung disease, and diabetes in adulthood 1.
Thus the birth weight of an infant broadly reflects the quality of its
intra-uterine development. It is an important parameter which could be
indicative of : (i) the immediate viability of the neonate; and (ii) the state
of maternal health/nutrition during pregnancy. From the public health
point of view, the mean birth weight in a community may provide a broad
indication of the quality of maternal health/nutrition care that is available
to it. Birth weights could be a useful criterion in monitoring trends with
respect to improvements in the quality of antenatal care 3.
Classification of low birth weight newborns 4,5
(independent of gestation)
i) Low birth weight (LBW)
=birth weight less than 2500g(upto and including 2499g).
(WHO1961)
ii) Very low birth weight (VLBW)
=birth weight less than 1500g (upto and including 1499g).
iii) Extremely low birth weight (ELBW)
=birth weight less than 1000g (upto and including 999g).
iv) Impossibly or incredibly low birth weight
=birth weight less than 750g (upto and including 749g).
Ideally, the definitions of low birth weights for individual populations
should be based on data that are as genetically and environmentally
homogeneous as possible 6.
Classification of newborns according to gestational age 4-6
(independent of birth weight) (WHO1950)
i) Pre-term newborns- Live born infants delivered before 37 completed
weeks (less than 259 days) are termed as pre-term newborns.
ii) Term newborns- Live born infants delivered between 259-293 days are
termed as term newborns.
iii) Post-term newborns- Live born infants delivered after 294 days or
more are termed as post-term newborns.
Dates are taken from the first day of the last menstrual period.
Weight for gestational age
Weight–for-gestational age at birth is often used to categorize an
individual infant as having experienced normal, subnormal (small for
gestational age or intrauterine growth retardation), or supra-normal
growth in utero. The classification most frequently used is:
i)
Small-for-gestational age(SGA or IUGR)
ii)
Appropriate-for-gestational age (AGA)
iii)
Large-for-gestational age (LGA),
although, strictly speaking SGA and IUGR are not synonymous 7.Some SGA
infants (e.g. those born to short mothers) may merely represent the lower
tail of the “normal” foetal growth distribution, while other infants who
have been exposed to one or more growth-inhibiting factors may actually
meet the criteria for AGA(e.g. those born to tall, well nourished cigarettesmokers).In individual cases, however, it is usually very difficult to
determine whether or not the observed birth weight is the result of true in
utero growth restriction, and classification of an infant as IUGR is
therefore based on the established cut- off for SGA. In fact, the higher the
SGA rate, the greater the likelihood that SGA is a result of IUGR.
Various criteria (i.e. cut–off points) have been used as the dividing
lines between these three categories. Those most commonly used are
based on percentiles of a distribution of birth weight–for-gestational age
derived from an accepted reference population; the 10th percentile is used
must frequently as the cut-off between SGA and AGA, and the 90th
percentile between AGA and LGA. These criteria have been applied in this
study.
Other definitions, such as <-2 or >+2 standard deviations (Zscores) from the reference mean, have also been applied1.
Regardless of which definition is used, the classification of a
newborn either SGA or LGA has implications for diagnosis, prognosis,
surveillance and treatment. SGA infants are more likely to have congenital
anomalies, and the observation that an infant is growth-retarded often
prompts a more careful physical examination or even laboratory tests
such as karyotyping. Laboratory cultures of biological samples and
serological tests of the mother and infant may occasionally reveal a
previously unsuspected intrauterine infection. The diagnosis of SGA may
also prompt closer examination of the placenta and reveal evidence of
infarction, single umbilical artery, velamentous insertion of the cord,
decreased placental weight, or previously unsuspected disease in the
mother1.
Regardless of the cause of the growth retardation, a severely
growth-related foetus or infant is at markedly increased risk of death,
hypoglycemia, hypocalcaemia, polycythaemia, and neurocognitive
complications of pre- and intra-partum hypoxia(i.e. in utero malnutrition is
associated with in utero deprivation of oxygen). Close monitoring of blood
glucose, calcium, haematocrit, and circulatory adequacy in the neonatal
period will allow timely intervention and should reduce the risk of adverse
secondary sequelae. Diagnosis of SGA should prompt actions to support
breast-feeding and in affluent populations where weaning food are
hygienically safe- may indicate the need for instituting a high energy diet
to maximize potential for catch-up growth in the first few postnatal
months. Over the long term, growth-retarded infants may exhibit
permanent mild deficits in growth and neuro-cognitive development1.
The diagnosis of LGA can also be important for the individual
infants. Large infants are at increased risk of birth trauma (including
clavicular fracture and brachial plexus injury), and of asphyxia secondary
to obstructed labour. The most common concern is maternal diabetes,
which may or may not have been diagnosed before or during pregnancy;
so monitoring (especially for the development of hypoglycaemia) is
important to permit institution of glucose therapy and thus prevent
adverse sequelae1.
Several publications have developed the concepts of proportionate
(also called Type 1, symmetric or “stunted”) and disproportionate (also
called Type 2, asymmetric or “wasted”) growth retardation, although the
importance of the distinction is still under discussion. Body proportionality
at birth may give information about the timing of growth retardation and
nutritional status of the newborn. Recent evidence indicates that the
proportionality among IUGR infants is strongly confounded by the severity
of the growth retardation or deficit in nutritional status and that, given
reliable estimates of gestational age, disproportionate IUGR infants tend
to be more severely growth retarded than their proportionate
counterparts1.
Symmetric LBW (Low Birth Weight associated with corresponding
low birth length) indicates maternal deprivation right from conception,
while asymmetric LBW (Low Birth Length with near normal length) points
to such deprivation especially in the last trimester3. The subsequent
growth performance of these two types is different.
Several large studies from different populations support the
independent association between indicators of body proportionality at
birth and a number of important neonatal or infant health outcomes.
Where valid assessment of gestational age is unavailable (as in
many settings in developing countries), size at birth and particularly birth
weight, can be used as the basis for decision regarding surveillance and
referral of small infants. Birth weight below 2500grams (LBW) is a
reasonable cut-off for instituting surveillance and/or referral for the
detection and treatment of early complications of pre-term birth or IUGR.
Surveillance of LBW, pre-term infants for complications should
include monitoring of oxygenation and respiratory status (including the
signs and symptoms of respiratory distress syndrome and neonatal
apnoea), indications of neonatal sepsis (e.g. apnoea, poor feeding,
vomiting, jaundice), and neurological complications possibly caused by
intraventricular haemorrhage (coma, seizures, apnoea, or focal
neurological deficit). Where adequate surveillance and treatment are not
possible locally, or the response to treatment is unsatisfactory, infants
should be referred to an appropriate health care establishment.
Surveillance and referral are even more important for very-low-birthweight (VLBW) infants, who are usually extremely pre-term.
Much higher proportions of LBW in North American whites and
Europeans are attributable to pre-term deliveries than in North American
blacks and Asians; for this reason, American white neonates with low birth
weights have poorer survival rates than American black neonates with
similar low birth weights 3. While pre-term infants with low birth weights
are at higher risk with respect to immediate survival as compared to LBW
term infants with similar low weights, their subsequent growth and
development in the event of survival is superior.
LBW in full term infants apparently has a significance, which extends
well beyond the neonatal period. Infants with LBW continue to grow in a
sub-standard growth trajectory, as compared with infants who start with
better birth weights. Intrauterine retardation, as reflected in LBW, has a
lasting, deleterious impact on growth, which even good diet and
environment can’t entirely reverse3. Maternal undernutrition and
consequent IUGR could programme body structure, physiology and
metabolism in a manner that increases the individual’s susceptibility to
degenerative cardiovascular disease in later life 3.
Whatever the explanation, these observations must be considered to
be of great significance in the context of the high incidence of LBW in
some countries of the region (e.g. Nepal, India and Bangladesh) on the
one hand, and the disturbing evidence for greater proneness of SouthEast Asians to diabetes and cardiovascular disease on the other.
So, research designed to identify (I) the factors contributing to the
high incidence of LBW and (II) the ways by which such high incidence can
be reduced, must be given high priority. Such research will serve two
major objectives of any national health/nutrition policy, viz, (I) achieving
optimal maternal nutritional status during pregnancy and (II) providing a
start in life devoid of irreversible handicaps for new generations of infants.
Mean birth weight:
Table 1 shows significant differences in mean birth weights of
babies in different parts of the world. South Asian Countries have the
lowest mean birth weight. Also, one-third of neonates in many South
Asian countries are of LBW 8.
Table 1: Mean birth weights in different parts of the world
Region
Mean birth weight (kg)
North America, Western Europe & Australia
3.5-3.6
Eastern Europe
3.1-3.3
Africa and East Asia
2.9-3.1
South Asia
2.7
Source: Low birth weight: A tabulation of available information, WHO/MCH/ 92.2,
Geneva, 1992.
Low birth weight incidence:
Generally accepted international criterion for low birth weight
is birth weight less than 2.5 kg. The overall incidence of LBW in Asia and
Africa is far higher than in North America and Europe (Table 2).
Table 2: Time trends in the prevalence of LBW
Region
Percentage prevalence of LBW
1979
1990
Asia
22
21
Africa
15
15
Latin America
13
11
North America
7
7
Europe
7
6
20
20
8
7
Developing countries
20
19
Developed countries
7
7
18
17
Oceania(Excluding,Japan,
Australia, New Zealand)
USSR
Global
Source: Same as table 1
Incidence of LBW in the countries of SEAR (South-East Asia Region)
are shown in Table 3.
Table 3: Mean birth weight and LBW in SEAR
Country
Number
LBW <2500g
Birth Weight (grams)
%
(mean ± SD)
India (1990)
4307
28.2
2633±417
Indonesia (1987)
1647
10.5
2936±415
Myanmar (1981-82)
3582
17.8
2852±469
Nepal (1990) Rural
2529
14.3
2787±416
3629
22.3
2760±498
Sri Lanka (1990)
1851
18.4
2841±458
Thailand
4124
9.6
3004±462
Urban
Source: Report of the WHO Expert Committee on the use of anthropometry for women
during the reproductive cycle and the newborn infant, 19939 .
In South Asia, the incidence of infants with LBW are:
Bangladesh50%
India
33%
Maldives
13%
Pakistan
25%
Sri Lanka 25%
[Source: The State of the World’s Children 1999, UNICEF.10 ]
Thus we can see that the incidence of low birth weight neonates in
developing countries is high. In Nepal, it varies from 14.3 to 23.3%. A
study11 done at B.P. Koirala Institute of Health Sciences (BPKIHS), Dharan
(1994) showed mean birth weight of 2680g, incidence of LBW newborns
as 14.28% and incidence of VLBW as 9%. According to the study of
Gautam M. 12 at four hospitals of the Kathmandu valley (1985), the
incidence of LBW babies was 23.3%. Studies done at TUTH (Teaching
University Teaching Hospital), Kathmandu13,14; reported the incidence of
LBW babies as 20.4%and 20.8% in 1988 and 1990 respectively. A study
at Maternity Hospital, Kathmandu by Dr. D.S. Manandhar15 has shown the
mean birth weight of 2770g and the incidence of LBW as 20.7%. Nepal
Multiple Indicator Surveillance (NMIS) fifth cycle16 reported incidence of
LBW as 19%.
World Summit for Children in 1990 has declared to bring down the
incidence of LBW to less than 10% by 2000 A.D.. In the health for all
target, 90% of infants or more will weigh at least 2.5kg by 2000A.D., has
been mentioned2. Likewise, HMG of Nepal has planned to bring down the
incidence of LBW to 23% and 12% of all births by 2002 A.D. and 2017
A.D. respectively17.
Inter-regional differences:
Inter-regional differences in birth weight are due to many factors.
North American and European women are taller, heavier, have better
weight gain during pregnancy due to better diet, and enjoy the benefits of
excellent ante-natal and obstetric care as compared to the majority of
women of developing countries. The only factors that contribute to LBW in
developed countries are pre-term birth, tobacco smoking, drug abuse and
genital tract infection. While this general assessment is largely true, there
are several other aspects related to inter-and intra-regional differences in
the incidence of LBW 3.
The reported incidence of LBW in Myanmar is less than in countries
of the Indian sub-continent. The incidence of LBW in Sri Lanka over two
decades ago, was nearly similar to the average levels now observed in
India. The incidence of LBW in Sri Lanka has now declined to 20%. It is
also reported that pre-term births account for nearly 50% of all LBW
neonates in Sri Lanka, a proportion much higher than in India (17%),
suggesting that the decline in LBW in Sri Lanka in recent years has largely
been due to a decline in LBW of term infants3.
The Nepalese Scene:
In Nepal, the quality of health care, the female literacy rate and the
acceptance of family planning vary widely between urban and rural areas.
So importance must be given to antenatal care, female literacy, diet,
poverty in order to decrease the LBW incidence.
Maternal anthropometric status:
Maternal height and weight significantly influence birth weight of the
babies13.
Effects of dietary supplementation during pregnancy on birth weights of
infants:
Several studies on nutrition in pregnancy and lactation have
reported that better diet and bed rest during the last few weeks of
pregnancy can bring significant measurable benefits in the form of
increased weight gain in pregnancy and higher birth weights of infants.
The role of Folic Acid:
Folic acid increases weight, DNA and protein content of the placenta.
The striking differences in LBW incidence in Thialand, Indonesia and
Myanmar, and in South Asia may be attributable to differences in folate
maternal status during pregnancy. Green leafy vegetables- a rich source
of folic acid-figure prominently in the diets of pregnant women in
Thailand, Indonesia and Myanmar but not in those of South Asia. So, in
the Indian sub-continent one major contribution towards improving the
nutritional status of pregnant women and the conditions of their neonates
could come through better dietary intake by pregnant women of green
leafy vegetables, which are not only a good source of carotene, but also of
folic acid, iron, Zn, Ca, and vitamin C. This will help in decreasing the
problems of vitamin A deficiency, anaemia and LBW. This will prove far
more rewarding in the long run to these countries than the misguided
approach by large-scale field trials with synthetic Vitamin A 3.
Influence of age at marriage
The average age of girls at marriage is much lower in developing
countries, especially Indian sub-continent e.g. 18.1 years in Nepal18. In
Nepal an estimated 40% of women between 15-19 years have given birth
to at least one child18. There is a significant increase in body weight and
height during adolescence. It has been suggested that the relative higher
incidence of LBW in South Asia, could be partly attributed to the lower
average age at marriage.
BMI(Body mass index):
The use of BMI as a method of detecting mothers who are possibly
at risk of delivering babies of LBW has been suggested by investigators in
SEARs as being a convenient index independent of age, parity and height.
Maternal Working Conditions:
In addition to mother’s anthropometric statuses, their occupational
and working conditions may also be related to the problems of LBW. It has
been reported that reduced placental blood flow in women working in a
standing position could be an important factor contributing to the
incidence of LBW in poor communities 3. This may cause the average
gestational age at delivery to shift to the left by a week in poor
communities. 95% of Nepali women work for 8 or 9 months of their
pregnancy16.
Altitude:
High altitude of residence of the mothers in Nepal can also be a
factor for high incidence of LBW 19.
Neonatal Anthropometric assessment in populations:
The prevalence of SGA can be used to select populations that should
be targeted for interventions. When SGA rates are not available, the
prevalence of LBW can be used as a proxy. Pre-term birth rates also
appear to be higher in developing countries, although most of the
difference in the incidence of LBW between developed and developing
countries is due to a disproportionately high incidence of LBW/SGA.
However, SGA prevalence is preferable both for targeting and for
assessing response, because few interventions have been found to
prevent pre-term birth1.
Recommended cut-off levels for triggering public health action have
not been established, but it seems reasonable to target those populations
with double the prevalence (i.e.>20% for SGA and >15% for LBW) found
in developed countries. Interventions might include nutritional
supplementation, anti-smoking campaigns, and malaria prophylaxis.
Within a given population, response to intervention can be assessed by
monitoring SGA rates (or VLBW and LBW if gestational age is unavailable)
over time. LBW and VLBW rates in excess of 15% and 2% respectively,
suggest a population at high risk for foetal and infant mortality and
morbidity, and for long-term adverse effects on childhood growth and
performance. Trends in developed countries over the past 20 years show
that, with no reduction in the prevalence of LBW and VLBW, foetal and
infant mortality can be dramatically reduced by adequate care of such
infants. Monitoring overall and birth-weight-specific foetal and infant
mortality is thus essential in assessing the response to interventions1.
Anthropometric assessment of newborns is an important research
tool for studying the determinants and consequences of impaired (or
excessive) foetal growth. Sometimes, specific local factors may play an
important aetiological role such as maternal tobacco-chewing, exposure to
indoor smoke, malaria or other tropical diseases, and HIV infection.
Similarly, although the immediate, life threatening sequelae of
severe IUGR are probably similar in all populations, the longer-term
consequences for child growth, development and performance may differ
across populations because of interaction with adverse post-natal
influences in disadvantaged populations, including socioeconomic,
nutritional factors as well as the level of medical care available. So,
investigation of such environmental factors and of interventions that
reduce adverse health sequelae should receive high priority in developing
countries where the prevalence of SGA is high.
Anthropometric assessment of neonates can also be important in
the context of nutritional surveillance. Periodic assessment of a population
overtime may show changes in the prevalence of SGA (or LBW as a proxy)
that could signal the effects of famine, epidemic infectious disease or
other adverse environmental circumstances1.
Selection of anthropometric indicators:
i) Gestational age:
Although the assessment of gestational age does not come under
the heading of anthropometry, it is mentioned first as any size-for-age
measurement requires reasonably valid and precise measure of age.
Mostly, especially in developing countries, gestational age is assessed by
calculating the number of completed weeks since the beginning of the last
menstrual period (LMP).
Early(<20 weeks)ultrasonic measurement of the biparietal diameter
(and/or femoral length, crown-rump length, or abdominal circumference)
could be considered the gold standard for assessment of gestational age1.
But, rigorous evaluation of this assessment in randomised controlled trials
has failed to reveal any benefit to maternal and peri-natal health, and it
cannot be recommended for routine use in all pregnant women1.
Other methods, such as assessment of fundal height or quickening,
are often used in clinical practice to confirm LMP-derived gestational age.
Physical or neurological examination of the newborn infant has also
been commonly employed in hospitals in developed as well as in
developing countries, although this has been found to produce significant
overestimates of gestational age for very pre-term infants. However,
these methods, especially in some of their simplified versions, could be
most useful for assessing gestational age of infants weighing ≥1500g at
birth in large field evaluations where other methods are not available.
ii) Birth weight:
This is the most widely used anthropometric indicator of size, for
which mechanical and electronic scales provide reasonably valid readings.
The most diagnostic classifications of foetal growth for both individuals
and populations are based on birth weight-for-gestational age.
iii) Birth body length(Crown-heel length):
It is another indicator of neonatal size, which can be used when
birth weight is not available. It frequently provides useful additional
information, since some neonates with low weight-for-age may be of
relatively normal length at birth. Several authors have pointed that a
discrepancy between weight and length deficits may be of aetiological
and prognostic importance. However, birth length is measured far less
precisely than birth weight, due to variations in posture and muscle tone
among neonates, and thus considerable training is needed to obtain
reasonably reproducible measurements.
iv) Birth head circumference:
Birth head circumference-for-age can be measured more precisely
than birth length, although the presence of head moulding may affect the
measurement. As with birth length, it (as an indicator of brain volume)
may provide important diagnostic and prognostic information beyond that
provided by birth weight alone.
v) Proportionality indices:
The most commonly used index of neonatal body proportionality
relates birth weight and birth length:
Rohrer’s ponderal index=
Birthweigh t ( g )
x100
( Birthlengt h, cm ) 3
vi) Other measurements:
Skin fold thickness has been used to assess newborn adiposity.
However, the determinants and consequences of variation in this
measurement are same as those of the anthropometric indices discussed
above. Since measurement of skin fold thickness is relatively imprecise, it
is not currently recommended for purposes of routine assessment 1.
In developing countries like Nepal, where majority of births are
conducted at home the measurement of birth weight is very difficult due
to non-availability of weighing machine. In these countries, other
anthropometric measurements-such as chest, arm, thigh and calf
circumferences, foot length-have been used as proxy measure of newborn
size20-23.
Arm and chest circumferences were considered as surrogates for
birth weights in a recent multi-centre WHO study of 400 births 20. Both
indicators demonstrated high correlation coefficients with birth weights
and high positive predictive values for LBW.
Studies in India 21,22 have evaluated the usefulness of calf
circumference as a proxy indicator for birth weight; results showed a
strong correlation between the two.
Even, foot length has a strong correlation with the birth weight and
other anthropometric indices. This has been shown by different studies 2326
. In Nepal, 91% of women deliver their babies at home 10 where the
measurement of birth weight is very difficult as weighing machine is not
available. So, in developing country like ours, it is essential to find out an
alternative method for estimation of birth weight. Various anthropometric
measurements mentioned above have been identified as proxy measure
for birth weight during first week of life, but they still require a health
worker for measurement. Identification of LBW babies delivered at home
can be enhanced if the tool used is simple enough to be used by the
mother/caretaker. Use of foot length as proxy measure of birth weight is
simple, cheap, easy to perform, rapid, requiring less handling and
disturbance to newborns. Even foot length measurement can be used to
estimate birth weight, length and surface area, which is especially
valuable in preterm babies nursed in incubators. This study is being done
to evaluate the usefulness of foot length as a proxy measure for birth
weight so that it can be used as a simple screening tool for LBW.