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Premature Neonatal Infants
Background
The
World Health Organization defined premature infants as live born infants who
delivered before 37 weeks from the last menstrual period. A small-for date
baby is what whose birth weight is more than two standard deviations below
the expected mean for the duration of gestation (Jolly, 1981). Lubechenco
(1976) defined any infant whose birth weight is at the tenth percentile or
less for his gestational age as small for gestational age.
Thus two major considerations govern
birth weight, the duration of gestation and the intrauterine growth rate.
Consequently, low birth weight (L.B.W.) that
is birth weight equal to or less than 2500 gm may be caused by a short
gestation (prematurity), intrauterine growth retardation or both (Kleigman
and Behrman 1978). L.B.W infants are also subclassified as very low birth
weight (V.L.B.W less than 2500 gm) and moderately low birth weight (M.L.B.W
1.501 to 2500 gm) while less than 1500 gm considered to be extreme L.B.W (Behrman,
1985).
Low
birth weight and prematurity have been the focus of many epidemiological
studies (Alberman, 1984) that have attempted to characterize their risk
profiles in order to advise prevention strategies (Hemminki, 1978) as they
have been long recognized as important predictors of infant mortality and
childhood morbidity (Mc Kormic, 1985).
Newly recognized childhood problems
that transcend the traditional boundaries of health care are becoming
increasingly important in practice of pediatrics. These include
emotional and behavioral problems, child abuse and neglect and non-organic
failure to thrive. These problems are responsible of morbidity in children
and their families (Haggerty et al., 1975).
Incidence, Morbidity and Mortality of premature and L.B.W. infants
L.B.W.
infants constitute a major public health problem in both developed and
developing countries. Twenty - one millions of L.B.W. Infants were
born in 1979 representing an overall incidence of 17% of all births that
year. Those born in developing countries made up more than 90% of the
total births (W.H.0., 1980).
During
(1981), 8.8% of live births in U.S.A weighed 2500 gm or less: the rate
for blacks was 12.5% while the rate for whites was 5.7%. Only one third of
L.B.W. Infants have gestational age of 37 weeks or more (Kleigman and
Behrman 1987).
In New Delhi, India, the incidence off
L.B.W infants was 30% of live births during 1968 - .1969 with I.U.G.R -
L.B.W. representing 78% of all L.B.W. infants (Viller, 1982). In
Egypt L.B.W infants was estimated by Abbassy et al., (1972), to be 10 - 13%
of all live births weighed less than 2500 gm. L.B.W. infants constitute a
group of neonates for which the risk of morbidity and mortality is elevated.
The 1958 mortality survey (Baulter and Bonham, 1963) stated that premature
babies had a mortality ratio 8 times higher than for mature infants.
In general, mortality rate is inversely proportional to gestational age and
birth weight (Brazia and Lubechenco, 1975). It is estimated that 85% of
neonatal deaths not due to anomalous fetal development are associated with
preterm delivery (Rush, 1982).
Potential causes of morbidity and mortality in
preterm and L.B.W infants
Hypoglycemia is the most important
problem in the small for date neonates with an incidence of 87%. For
premature infants; the incidence is only 15%. Various mechanisms have been
postulated for the development of hypoglycemia including reduced
hepatic glycogen available
for glycogenolysis, reduced fat stores, reduced activity of glycolytic or
gluconeogenetic enzymes and increased rate of glucose utilization (Jones and
Robertson, 1984).
Hyaline membrane disease occurs most frequently. Mortality is highest in
infants of shortened gestation and falls progressively with increasing
gestational age (Avery et al., 1981).
Intrapartum asphyxia may affect small for date infants, particularly if they
are disproportionately growth retarded (Walter and Reameakers, 1982). This
may be due to deficient glycogen stores. Intrapartum asphyxia will increase
the risk of development of meconium aspiration syndrome and pneumonitis in
these infants (Yeh et al., 1977).
Hypothermia is one of the major
problems encountered in small for date infants. Their problems are with
excessive heat loss and with generating heat (Sinclair, 1970). Heat
loss is increased in these infants due to (a) lacking subcutaneous fat (b)
bigger surface area/ body weight ratio (c) absent brown adipose tissue. The
premature infant's ability to
control body heat is impaired due to immaturity of their anatomic structures
or physiological and biochemical functions (Kleigman and Behrman,
1987).
Hemorrhage whether associated with
trauma, asphyxia, infection or defect of the clotting mechanism is frequent
often sever in L.B.W. infants. Increased
capillary fragility, hypernatremia, and increased vascular
pressures may be contributing factors (Kleigman and Behrman,
1987).
Hypothermia is frequent in mature
small for date infants. It may be as a result of a rise in fetal
erythropoietin response to chronic inutero hypoxia (Wirth et, al., 1979).
Polycythemia causes hypervesicosity which may be manifested by C.N.S
depression, heart failure and respiratory distress syndrome (Johnes and
Robertson, 1984).
Infections are the most important
illnesses affecting premature and L.B.W. infants. There is 3 - 10 fold
increase in the incidence of sepsis, meningitis or U.T.I. in these
infants than in full term normal birth weight infants (Johns and overall,
1987).
Recurrent apnea is
defined as cessation of
breathing for more than 20 seconds or long enough to produce cyanosis or
bradycardia. It has a very high incidence in infants under 1500 gm or under
32 weeks gestational age (Behrman, 1987).
Congenital malformations occur with greater frequency in infants of L.B.W.
than in all live births. There is a high malformation' rate in both
preterm and in full term small for gestational age infants (Kleigman and
Behrman, 1987).
Retrolental fibroplasia occurs in
premature infants treated with oxygen at concentrations above air levels.
The increased arterial oxygen tension that result may lead to severe damage
to the immature retina (Biglan
et al., 1984).
Patent ductus arteriosus is virtually
present in all infants whose
birth weight is less than 1750 gm, in the first 24 hours of life. Beyond
this time, the number of infants with continued patency is greater in L.B.W.
groups. A large left to right shunt via ductus arteriosus increases
the morbidity and mortality of the respiratory distress syndrome in neonates
(Reimenschneider, 1964).
Definition and
classification of the newborns
Newborn infants are divided into three groups
according to their gestational age
(Hutchison, 1980):
(1) Preterm neonates
Less
than 37 calculated weeks of gestation (less than 259 days)
(2) Term neonates
From
37 to 41 calculated weeks of gestation (259 - 293 days).
(3) Post term neonates
42
weeks of gestation or more (294 days or more).
The
calculation begins from the first day of the last menstrual period.
Each group is then subdivided according to birth weight in relation to
gestational age into the following groups (Lubchenco et al., 1963):
(1) Small for gestational
age (S.G.A.):
These are all infants whose weight is
below the 10th percentile for their respective weeks of
gestation.
(2) Appropriate for
gestational age (A.G.A.):
Infants whose weight is between 10th percentiles for their respective weeks
of gestation.
(3) Large for gestational
age (L.G.A.):
Infants whose weight is above 90th
percentile for their respective weeks of gestation.
So, we
have nine groups of newborns (Davis et al., 1972):
|
Preterm
SGA |
Preterm AGA |
Preterm
LGA |
|
term SGA |
term
AGA |
term
LGA |
|
Post
term SGA |
Post term AGA |
Post
term LGA |
Maternal factors affecting birth weight and gestational age of the newborn
infant
(1) Age of the mother:
The highest incidence of L.B.W. has
been found among mothers under the age of 20 years. The incidence then falls
as the age increases but it rises again after the age of 30 - 35 years.
Elderly primigravidae above the age of 35 years have three fold risks of
preterm delivery and small for date infants when compared with primigravidae
between 20 - 25 years (Bulter and Alberman
1989).
(2)
Maternal height and weight:
The
physical characteristics of the mother are strong indicators for the risk of
delivery of a premature or small for date baby. When the mother weight
before pregnancy is less than 20 Kg or the mother height less than 1.5
meters, the risk is increased (Papiernik, 1984). For instance, the rate of -
preterm birth in women who are less than 1.52 meters in height is twice as
that of women who are taller than 1.72 meters (Fedrick and Anderson, 1976).
(3) Socioeconomic status of the
mother:
Many investigators have shown that the
average birth weight is lower and therefore the incidence of L.B.W is higher
among the poor sections of any community (Crosse, 1975). Papiernik (1984)
suggested that three essential components can be distinguished within each
social class, the physical effort done by the mother,
the access to information including the educational level and utilization
and effectiveness of the available health
services.
(4) Work and physica1 exertion:
All women work at home, some are also
in paid employment at a formal place of work. This is an add load and
they have also to travel between the 2 places of work as well as specific
hazards at each site (chemicals or irradiation). As this increases so
does the incidence of preterm labour (Chamberlain, 1984).
Clapp and Dickstein (1984), studied the
relation between maternal. exercise prior to and during pregnancy and the
fetus outcome, and they found a high incidence of small for dates
infants and preterm deliveries among women who maintained their
preconceptional level of exercise throughout pregnancy.
(5) Parity and birth order:
Repeated child birth imposes several physical and nutritional demands on the
mother. The incidence of prematurity and low birth weight for gestational
age is consistently high when birth interval is less than 2 years or more
than 6 years, the safest interval being between 3 and 6 years (Douglas,
1950). The birth weight is also lower in the first pregnancy than in
subsequent pregnancies and rises with parity (jolly, 1961).
(6) Maternal nutrition:
Maternal pregnancy weight and
pregnancy weight gain are two independent variables that can affect fetal
growth. Underweight mothers and those
affected with malnutrition deliver infants
with diminished birth weight (Kleigman and Hulman, 1987).
Additional calories, rather than protein supplementation correlates best
with enhanced fetal weight. Poor nutrition may affect the strength of
membranes which correlate with premature rupture of membranes and preterm
delivery (Rush 1982)
Studies done by Shah and Rajalakashmim (1984), suggested that a poor vitamin
A status is one of the features associated with a higher prevalence of
prematurity and intrauterine growth retardation
Also,
maternal zinc depletion is associated with intrauterine growth retardation,
neurologic dysfunction and malformations in both animal and human beings
(Simmer and Thompson, 1985).
(7) Maternal vascular diseas:
Vascular diseases, mainly hypertensive
states are responsible for about one third of fetal growth retardation (Kierse,
1984). This effect is related to the duration of hypertension and to the
absolute elevation of diastolic pressure and it is most severe in the
presence of end-organ disorders such as retinopathy (Kliegman and Hulman,
1987).
The frequency and
severity of growth retardation is
highest in pregnancy induced
hypertension superimposed on
pre-existent hypertensive disorders (Kierse,
1987).
(8) Maternal infection:
Intrauterine infection was estimated by Knox, (1978) to be responsible for
up to 10% of all growth retarded fetuses.
Fortunately, not all maternal viremias, parasitemias or bacteremias result
in placental or fetal colonization or disease. Generally, the severity,
duration of infection, immune status of the mother and fetus,
length of gestation , and type and virulence of the infecting agent,
all contribute in varying amounts to the probability of in-utero infection
and subsequent degree of growth retardation or prematurity (Varner and
Galask,1987).
In congenital rubella, there is
increased incidence of L.B.W. Up to 60% of
infants with congenital rubella may be below the
tenth percentile of weight for gestation (Copper et al., 1965), but in
contrast to many other causes of growth retardation, liver and spleen are
rather larger for body weight and brain growth is not protected (Naeye and
Blanc,1965). The rubella virus shows predilection for infecting the vascular
endothelium and~ may cause placental villous damage by inducing necrosis in
the endothelium of the villous capillaries (Driscoll, 1969).
Cytomoga1ovirus infection is the
commonest cause of congenital viral infections. About 90% of infants
with C.M.V. infection have no clinical manifestations at birth. Some may
reveal multitude developmental abnormalities within the first two years of
life. Some degree of growth retardation occurs in approximately 70% of
infants who present clinical manifestations at birth (Stango et al., 1983).
C.M.V infection causes cell and tissue injury as a result of lytic cell
death and focal necrosis (Knox, 1978).
Varicella Zoster virus infection
especially in early pregnancy can cause I.U.G.R. It may impair both growth
and differentiation, although some infants with severe malf6rmations were
found to of appropriate size for gestation between varicella infection
during pregnancy and preterm labour and delivery.
Herpes
virus infection in early pregnancy has been reported to affect the fetus.
This is probably due to transplancental acquisition secondary to viremia.
Although rare, congenital malformations have been reported with intrauterine
growth retardation (Varner and Galask, 1984).
Influenza virus infection may produce viremia and may result in congenital
infection with an increased incidence of intrauterine growth
retardation. Stillbirth and varying amounts of neonatal morbidity
have been reported (Lehman, 1971).
Infectious hepatitis virus can be
transmitted to the infant either if the mother is an asymptomatic carrier or
if she develops the disease. Although the virus is usually transmitted at
the time of delivery or during the peurperium, transplacental transfer of
the virus has been documented. The major risk of the fetus is
prematurity. The incidence of newborns with L.B.W. is increased when
hepatitis B occurs during pregnancy. This has also been reported in
mothers contracting hepatitis A in pregnancy (Waterson, 1979).
Toxoplasmosis infection causes
parasitemia which transferred transplacentally to the fetus. Although severe
fetal damage is more likely to occur with primary maternal infection in the
first trimester, they are likely to cause less chronic problems in the
neonates than are maternal infections in the third trimester. Although
I.U.G.R has been reported, the classic findings include hydrocephalus or
microcephaly, chorioretinitis, convulsions and intracranial calcifications
(Varner and Galask, 1984).
Malaria
is one of the most common infectious
diseases in the world, being endemic in most tropical areas. I.U.G.R. Occurs
as a result of multiplication of protozoa in the placenta. It has been
reported that it also increases frequency of abortion, stillbirth and
premature labour (Varner and Galask, 1984).
Congenital syphilis has become extremely rare. It is not uncommon to find
I.U.G.R. listed among the possible consequences of syphilitic infections
(charles3 1983).
Bacterial infections are not well
studied although most are transmissible to the fetus and some, such as
listeria mono-cytogenes, may cause serious disorders such as preterm
delivery, neonatal pneumonia and meningo encephalitis (Hurley, 1983).
(9) Irradiation and drugs:
From the data reviewed by Brent and
Jensh (1967), there is adequate clinical evidence that high dosage ionizing
radiation during pregnancy may result in severe growth retardation. The
effects of maternal drug administration on the fetus are usually considered
primarily in term of teratogenicity. Certain drugs appear to affect only
some and not all parameters of growth, for instance small head
circumferences without differences in length or weight following
antiepileptic therapy with carbamazepine (Hiilesma et al., 1981).
Cytotoxic drugs and chronic administration of corticosteroids in pregnancy
are possible causes of growth retardations (Scott, 1977).
(10) Race:
There is difference in the mean birth
weight by gestation of the white and black populations of U.S.A. whilst the
white babies are heavier in most of the mature gestational periods, below 35
weeks; the black babies are larger on the average
(Niswander and Gardner, 1952).
Garn et al., (1977) have reported that
the black women have 9 days less gestation time than white women; with twice
the rate of preterm births. It is difficult to define the different
components which could be responsible for such difference socioeconomic
factors have a large part in the explanation. However, ethnic factors
(genetic or racial) are important also.
(11) Past obstetrical
history:
The
reproductive behavior usually repeats itself as reported by Bakketeig,
(1977). He reported that a previous low birth weight is a
reasonable predictor of a second low birth weight. ~g founded also that a
low gestational age was a much more powerful in predicting a second preterm
birth.
(12) Maternal conditions associated
with hypoxemia:
Nutritional anemia is not usually
associated with aberrant fetal growth.
Anemia and low hemoglobin levels vary with
poor socioeconomic status 3 poor general nutrition and other factors known
to be associated with L.B.W. (Bulter and alberman, 1969); it is probably
fair to conclude that
Heart disorders
affect less than 1% of the pregnant women.
By far the most common is chronic rheumatic heart disease. Congenital
heart disease is also increasing in importance since many patients with
these conditions now survive childhood, but still have residual defects
(Knox, 1986). Barnes, (1983) demonstrated I.UG.R. in patients in whom the
disease was severe enough to cause polycythemia.
Bronchial asthma is the only chronic
obstructive lung disease encountered with
significant frequency during pregnancy. Most series demonstrated increased
frequency of premature labour and L.B.W. infants in asthmatics (Gruiksbank,
1986).
High attitudes present the birth
weight to be smaller than usual at all periods of gestation. The placental
mass is hypertrophied in order to compensate for the lower circulating
oxygen saturation (Howard et al., 1957).
(13) Maternal renal diseases:
Mc Grady et al., (1985) found that
L.B.W. and premature infants were more frequent in urinary tract infections
associated with pregnancy than in
control pregnancies.
In chronic parenchymal renal disease,
the fetal outcome depends on the degree of impairment of renal
function and the incidence of complications
(Katz et al., 1980)
(14) Maternal endocrinal
disorders:
Endocrinal disorders do not appear to have major Consequences for fetal
growth although lower weight for gestational age has been reported in
infants born to mothers with
Addison's disease(Osler, 1962), hyporthyroidism (Montgomery and Hardy, 1977)
and hypothyroidism (Kaltreider and Kohl, 1980).
There
is evidence of a delayed initial growth in diabetic pregnancies but which
may later clouded or compensated for by macrosomic influences and excessive
fat deposition (Pederson and Pederson 1979). In diabetic pregnancy,
prematurity due to preterm labour and elective preterm delivery for maternal
complications such as preeclampsia are common (Knox, 1986).
(15) Maternal drug dependence:
Smoking is well known to affect birth weight. Also, the length of gestation
recorded to be less than mothers who never smoked (Chamberlan, 1984). Many
factors such as nicotine, carbon monoxide, reduced uteroplacental blood flow
or reduced maternal food intake may contribute to lower weight for gestation
- associated with smoking during pregnancy (Pirani, 1978).
Alcohol intake was described by Kierse,
(1984) to reduce fetal growth. Fetal alcohol syndrome is characterized
by (a) prenatal growth retardation (b) characteristic facial dysmorphology
(c) congenital malformations mostly skeletal, cardiac and genital (d)
disturbances of mental development (Kierse, 1984).
Narcotics like heroin appeared to shorten gestation and reduce weight for
shorten (Rementeria and Lotongkhum, 1977).
Other Factors Affecting The Birth Weight And Gestational Age of the newborn
infant
1- Sex of the baby:
Boys
are being born a little heavier than girls on the average. This effect
is present through pregnancy even in earlier period (Chamberlain et al.,
1975).
2- Multiple pregnancies:
It is associated with L.B.W. It
has a greater effect on intrauterine growth than on the length of gestation
(Crosse, 1975). During multiple pregnancies, the hormone production is
increased and consequently, the placental bulk greatly increased. Such high
estrogen levels in tissues could be associated with an easier triggering of
labour contractions in the myometrium (Chamberlain, 1984).
3- Placental influences:
Fulfillment of fetal nutrients and energy requirements depend on the
transfer across the healthy placenta.
Intrinsic placental malformations are not a major cause of
fetal growth retardation (Kierse, 1984). Growth retardation relates
mainly to defective uteroplacental circulation
4-
Uterine bleeding:
It is
a high predictive value in preterm labour (Bulter and Bonhan, 1963).
Abruptio placenta may be associated with preterm labour and some
publications also linked placenta previa in late pregnancy with antepartum
hemorrhage and preterm delivery (Papienrick, 1984).
5- Premature rupture of the
membrane:
It
leads to expulsive uterine contractions and preterm labour. It may be
caused by incompetent cervix, polyhydramnios, multiple pregnancies and
vaginal infections (Evaldson et al., 1980).
Assessment Of Neonatal Maturity
An
accurate estimate of gestational age is necessary in the management of the
ill or premature infant. Gestational age is assessed in both physical and
neurological criteria. The Dubowitz method (Dubowitz et al., 1970) for
assessing gestational age is the best evaluated and most reliable method for
this purpose. The Dubowitz method comprised 11 external criteria. The
external criteria include the following physical features: (1) the presence
and extent of edema, (2) Lanugo hair and (3)
Planter creases as well as (4) an assessment of the texture (5) colour and
(6) opacity of the skin (7) degree of nipple formation, (8) breast size, and
(9) genital development and (10) external ear form and (11) firmness. These
items are graded on a 2-4 point scale (See
Figure).
The Dubowitz method comprises
neurological items, some neurological criteria overlap with those recorded
in the Dubowitz neurodevelopmental assessment protocol, but those in the
gestational assessment scheme are chosen because they alter little with
neurological compromise. These are graded on a 3-4 point scale as described
by Dubowitz (1970); it can be carried out at any time during the first five
days of life provided that there is no evidence of intrapartum asphyxia or
birth trauma (See
Figure).
At the
end of the examination all the points are totaled and the gestational age
read off from a nomogram (Dubowitz, 1970) (See
Figure).
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