INTRODUCTION
The placenta is the most important organ for
maintaining and continuing healthy pregnancy. It transfers and exchanges oxygen
and contortion needed for the fetus. The estimation of the placenta would demonstrate
important information about whatever has happened on the fetus that careful extenuation
of the placenta can provide insight regard the inutero-environment of the fetus
before delivery. As fetus grows, many changes happen in placenta shape and
function that reflect changes in needs of fetus in different growth stages. To
achieve these metabolic immunologic and endocrine changes should happen in
placental trophoblast.
Placental weight reflects placental development and
function and is correlated with maternal age, gestational age, history of maternal
diabetes, pre-eclampsia, birth weight, parity route of delivery, infants gender
Apgar score and fetal distress. Other factors influencing placental weight includes
party, maternal height and weight and serum ferritin contraction (but not serum
haemoglobin concentration).
Barker et al reported that growth of the placenta was
a predictor of maternal medical diseases including cardiovascular disease,
hypertension and diabetes mellitus. Other factors that could affect the
placenta weight are race and socio-economic status.
Large
placental size and low birth weight have been implicated as factors predicting
high blood pressure in adulthood. it has been shown that maternal or fetal
diseases(gestational diabetus, severe anemia, hypertension, hydrops
fetalis)influence fetal and placental weight. it has been shown that placental
weight has a significant role in fetal growth in terms of terms of weight, body
length and cord length.
Placenta weight
The delivered placenta is “deflated” compared to its
state in utero, a consideration for anyone attempting ultrasound or anatomic
correlations. The average diameter of the delivered placenta at term has
reported as 18-5cm (range 10-5 to 24.5cm), with a mean thickness of 2.3cm
(range 1.1 to 4.1cm). the same source descried the early growth of the placenta
as primarily an increase in diameter of the chorionic disc, while in the later
stages of gestation, placental weight increased primarily due to increase in
placental thickness. They likewise reported that mean diameters of the placenta
at the third to six months as 5.8cm 8.2cm, 10.8cm, and 13.0cm, respectively the
number of major villous trunks remains constant; therefore, placental growth
requires that each major trunk (established in the early months of gestation)
must arborize or otherwise develop proportional to the increase in placental
weight from early gestation to delivery. Schneider has recently reviewed the
ultrasound data regarding placental volume in the mid trimester. The mean
increase in placental volume between 16 and 24 weeks was 31, - +, 8cm3;
further placental volume in the second trimester was dusty correlated with
infant birm weight, suggesting that mid trimester placental well being is an
important determine of late fetal grown.
Expected Fetal and Placental Weight
Ratio
|
Weeks
|
Placental
|
Fetal
|
F.P
|
|
Estuation
|
Weight (g)
|
Weight (g)
|
Ratio
|
|
8
|
6
|
1
-1
|
0
-18
|
|
10
|
14
|
5
|
0-36
|
|
12
|
26
|
17
|
0.65
|
|
14
|
42
|
30
|
0.71
|
|
16
|
65
|
60
|
0.92
|
|
18
|
90
|
130
|
1.44
|
|
20
|
115
|
250
|
2.17
|
MATERNAL WEIGHT
Most
of the eight gained during pregnancy is attributed to the uterus and its contents,
the breast increase in blood volume and extra cellular fluid. A smaller
fraction of the increased weight as the result of metabolic alterations known
as maternal reserves (Cunningham et al 2005).Approximately 62% of the weight
gained consists of water, which is retained in all system of the body.
While
initial maternal weight and the weight gained during pregnancy are highly associated
with birth weight, it remains unclear what role maternal fat or water have in
fetal growth. studies in well nourished women at term suggest that maternal
body water rather than fat contributes more significantly to infant birth
weight(Cunningham et al 2005).The recommended patten for normal weight gain is
approximately 3kg in the first trimester followed by about 0.4kg/week for the
remainder of the pregnancy. This pattern results in approximately 3kg of fat
stores accumulating in the first half of pregnancy. While weight gained in the second
half goes towards the growth of the fetus and maternal supportive tissues.
Fetal
growth is slow in the first 2months during organogenesis but then accelerates
rapidly. maximum growth rate is achieved between the 4th and 8th
month when the fetus grows at the rate of 5-9% per week .Until 15-16weeks the
placenta is larger than the fetus but by term the fetus is five to six times
heavier than the placenta. Amniotic fluid increases from 7ml at 8weeks, 30ml by
10weeks, 190ml by 16weeks, to a mean of about 800ml by 35weeks after which it
decreases to about 400ml by 42weeks.The increase in the weight of the uterus is
more rapid in the first 20weeks (Blackburn 2007),the weight of the breast,
blood volume and total body water increases steadily thought out pregnancy. The
pitting oedema of ankles and legs, which is seen in most pregnant women,
especially at the end of the day may amount to over 1L.
There
is currently no official recommendation for weight gain during pregnancy. Weight
gain averages between 11 and 16kg but variations are large. A birth weight of
3.1-3.6kg has been associated with optimal maternal and fetal outcomes.
Maternal nutritional status at the time of conception is very important for
fetal growth and development, it is important to attain a healthy body weight
prior to conception.
Table showing the distribution of an
average increase in weight
Maternal Weight gain (kg)
Percentage of total Wt
Uterus 0.9
Breast 0.4
Fat 4.0 64%
Blood 1.2
Extra
cellular fluid 1.2
Total 7.7
Fetal
Fetus 3.3 25%
placenta 0.7 11%
Amniotic
fluid 0.8
Total 4.8
Grand
total 12.5
The placenta weight and fetal weight
The ability of the fetus to grow and thrive in
utero depends on the placental function and the average weight of the placenta
at term is 508g. The ratio between placenta weight and birth weight of the
newborn is 1: 6. However, methods of measurement vary widely particularly due
to differences in placental preparations. Placental weight and its relationship
to infant size at birth have been studied for more than a century. Past studies
indicated that placental weight was associated with pregnancy outcome. High placenta
weight was associated a poor perinatal outcome, a low Apgar score, respiratory
distress syndrome and perinatal death, whereas a low placental weight was
associated with medical complications in the mother.
Clinical
associations with placental weights and fetal placental ratio have been
documented; for example, small placentas maybe associated with trisomies where as
large placentas may be associated with maternal diabetes. Disproportionately
large placentas (low fetal/ placenta ratio) could reflect acute placental
injury resulting in villous edema or a chronic process requiring placental
overgrowth, such as maternal anemia or malnutrition. Disproportionately small placentas
(high fetal/placenta ratio) maybe seen in maternal hypertension, and may result
in fetal distress or low Apgar scores. Recent birth weight tables shows fetal
birth weights at term have increased overtime. There is a positive correlation
between fetal weight and placental weight.
One of the influencing factors on
placental weight is gestational age. Gestational age is known as a principle
and determinant fact of placental weight. Kinare et al stated that the capacity
of fetal weight growth is determined by placental growth and between placental
volume in 15 to 18 weeks gestation ages to placental weight at birth and birth
weight found significantly correlation. Placental weight increases in infants
proportionately with gestational age, while in infant with small for
gestational age (SGA) were not seen any change from 36 weeks gestation. Lo et
al have proved there is no significant difference between placental weight and
gestational age. In different studies it has been demonstrated that male fetuses
gain significantly greater weight as compared to female fetuses from the 34th
-42nd week of gestation. Because placental weight has a relationship
with infant weight these should be a significant correlation between infant sex
and placental weight.
Baby’s Weight
In first world nation the average weight of a full-term
newborn is approximately 3.4kg (7½ lbs), and is typically in the range of
2.7-4.6kg (5.5-10 pounds) over the first 5-7 days following birth the body
weight of a term neonate decreases by 3% - 7% and is largely as a result of the
reasorbtion and urination of the fluid that initially fills the lungs, in
addition to a delay of often a few days before breast-feeding becomes
effective. After the first week healthy term neonates should gain 10-20 gram/kg/day.
Factors that determine the Birth weight of
a baby
·
Infant gender
·
Multiple factors
·
Size of the
parents
·
Birth order
·
Baby’s health
·
Maternal factors
such as race and ethnicity, nutrition and current and previous pregnancy
medical risk characteristics.
SUMMARY
There
is an increase weight gain during pregnancy especially the first half of pregnancy.
While weight gained in the second half goes forwards the growth of the fetus.
Fetal growth is slow in the first two months during organogenesis but this accelerates
rapidly maximum growth rate is achieved between the 4th and 8th
month when the fetus grow at the rate of 5-9% per week. Until 15-16 weeks the
placenta is large than the fetus but by term the fetus is five to six times heavier
than the placenta.
It was reported that an altered
growth of placentas was a predictor of maternal medical diseases including
cardiovascular disease, hypertension and diabetes mellitus. Other factors such
as race and socio-economic status also affect the placenta weight. Also a woman
with diabetes mellitus tends to have a large baby than a normal pregnant woman.
Studies have shown that the male
fetus gain significantly greater weight when compared to female fetus from 34th
to 42nd week of gestation. Because placental weight has a
relationship with infant weight, there should be a significant correlation between
infant sex and placental weight.
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Blackburn 2007 maternal, fetal and neonatal physiologhy,
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Cunningham F, Leveno K, Bloom et al 2005 Williams
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