PLACENTATION

INTRODUCTION
The placenta is a temporary organ of pregnancy located in the uterus.
 It is formed from fetal and maternal components.
The fetal portion is formed by the chorion frondosum, while the
maternal portion is formed by the decidua basalis.
Moreover, the placenta is the meeting point of two circulatory
systems: fetal circulation and maternal circulation.
The main function of the placenta is the interchange between the
mother and the fetus.
 it provides nutrition and oxygen to the fetus and removes waste
material and carbon dioxide.
Various processes before and during implantation: ovulation, fertilization, cleavage,
blastocyst, trophoblast differentiation, decidual change, hatching of blastocyst, and
penetration defect
Stages of implantation: (A) Hatching blastocyst; (B) Adhesion of blastocyst to uterine epithelium;
(C) Penetration of blastocyst through uterine epithelium and erosion of endometrium; (D) Closure
of penetration defect and differentiation of trophoblast and embryoblast
Decidua Definition:
It is the functional stratum (stratum compactum) of uterine
endometrium after the implantation of blastocyst .
The “word decidua” means falling off as this part of endometrium
separates and falls off during childbirth.
Change in endometrium:
After implantation, the features of the endometrium, maintained and
intensified under the influence of the hormone----- the human chorionic
gonadotropin (hCG) secreted by the cells of syncytiotrophoblast.

On 17th or 18th day of menstrual cycle, i.e. 5th day after fertilization
and at the time of implantation, the uterine endometrium is highly
modified, edematous and vascular
Decidual reaction:
Due to the higher levels of maternal progesterone and the hCG, the
stromal cells enlarge, become vacuolated and filled with glycogen
and lipids (decidual transformation).
These cells are called decidual cells.
The intercellular substance increases, and it gives edematous
appearance.
 This change in the endometrial stroma is called the decidual
reaction.
 The glycogen and lipids provide nutrition to the early embryo until
the placenta takes over this function.
The saw-toothed appearance of endometrial glands increases and
the blood vessels of endometrium become more twisting.
The decidual reaction is a defensive mechanism to protect the
endometrium.
Subdivisions of Decidua
1.Decidua basalis/Serotina: The part that
contributes for the maternal component of
placenta. lies deep to the developing
blastocyst--- maternal blood vessels (spiral
arteries) proliferate in the region of decidua
basalis and are filled with blood and dilate to
form sinusoids.
• consists predominantly of large decidual cells
that contain large amounts of lipids and
glycogen---- also referred to as the decidual
plate, and is firmly united to the chorion.
2. Decidua capsularis/Reflexa: The part of
endometrium that surrounds the embryo like a
capsule and separates it from the uterine cavity.

3. Decidua parietalis/Vera: The part of decidua

that lines the rest of uterine cavity
Fate of decidua:
As the conceptus enlarges during development, the decidua
capsularis enlarges into the uterine cavity and finally fuses with
decidua parietalis during 3rd month of pregnancy thus
eliminating the uterine cavity.
At the end of pregnancy, the decidua is shed off, along with the
placenta and membranes.

It is this shedding off which gives the decidua its name
Chorion and Formation of Chorionic Villi
Chorion : The cellular, outermost
extraembryonic membrane composed of
trophoblast, lined with extraembryonic
somatopleuric mesoderm.
Formation
The extraembryonic somatic mesoderm
and the two layers of trophoblast
(cytotrophoblast and syncytiotrophoblast)
contribute for the formation of chorion all
around the developing embryo .
 The extraembryonic coelom is now
called the chorionic cavity.
Embryo and its amniotic and yolk sacs
are suspended into it by connecting stalk.
The amniotic sac with embryonic
epiblast forms its floor and the yolk sac
with embryonic hypoblast forms its roof
Types of Chorion
Chorion laeve:
The villi associated with decidua
capsularis are temporary.
As the gestational sac grows
they get compressed and their
blood supply is reduced
Chorion frondosum:
 The chorionic villi associated with
decidua basalis retain the
vascularity, undergo considerable
development and form a bushy
area called chorion frondosum.
This contributes fetal part of
placenta as the maternal part is
Stages in the Formation of Chorionic
Villi
 The structural component of chorionic
villus differs at different periods of
embryonic development.
 Accordingly there are three types of
chorionic villi.
1. Primary villi: They consist of a central
core of cytotrophoblast covered by a
layer of syncytiotrophoblast. Adjoining
villi are separated by an intervillous space.
2. Secondary villi: These show three
layers. Outer syncytiotrophoblast, an
intermediate layer of cytotrophoblast,
and an inner layer of extraembryonic
mesoderm.
3. Tertiary villi: These are like secondary
villi except that there are fetal blood
capillaries in the mesoderm.
Meanwhile, cytotrophoblastic cells in the
villi penetrate progressively into the
overlying syncytium until they reach the
maternal endometrium.
Here they establish contact with similar
extensions of neighboring villous stems,
forming a thin outer cytotrophoblast
shell .
This shell gradually surrounds the
trophoblast entirely and attaches the
chorionic sac firmly to the maternal
endometrial tissue .
Villi that extend from the chorionic plate
to the decidua basalis (decidual plate: the
part of the endometrium where the
placenta will form; are called stem or
anchoring villi.
Those that branch from the sides of
stem villi are free (terminal) villi----
through which exchange of nutrients and
Longitudinal section through a villus at the end of the fourth week of development. Maternal vessels
penetrate the cytotrophoblastic shell to enter intervillous spaces, which surround the villi. Capillaries in
the villi are in contact with vessels in the chorionic plate and in the connecting stalk, which in turn are
connected to intraembryonic vessels.
Further Development of the Placenta
• The placenta presents two parts (fetal and maternal),
• two surfaces (fetal and maternal),
• two types of cotyledons and a peripheral margin.
Maternal part: This is contributed by decidua basalis or decidual plate
of endometrium.
Fetal part: This is contributed by chorion frondosum or chorionic
plate. This surface is covered by the fetal membrane amnion and the
umbilical cord is attached near the center of this surface.
Maternal surface: The maternal surface is rough and
irregular ---- It is subdivided into a number of lobes called
maternal cotyledons--- Septa that grow into the
intervillous space from the maternal side divide this surface
into 15–20 rough and irregular maternal cotyledons.
If the placenta is viewed from the maternal side, the bases
of the septa are seen as grooves while the cotyledons
appear as convex areas bounded by the grooves.
Fetal surface:
 This surface is smooth and is covered by amnion .
 The umbilical cord is attached close to the center of this
Placenta: (A) Maternal surface; (B) Fetal surface
surface.
 Umbilical vessels radiate from the umbilical cord beneath
the amnion.
 The fetal part is contributed by chorionic frondosum that
is seen as a plate called chorionic plate.
 From the chorionic plate 40–60 extensions (fetal
cotyledons) arise and extend toward the decidua basalis.
Their terminal effects look like fingers and are called chorionic
 The villi that are attached to decidua basalis are called
anchoring villi.
 Others float in the maternal blood that flows in between the
villi and are called floating villi
Maternal and fetal cotyledons:
There are 15–20 maternal
cotyledons in placenta.
Each maternal cotyledon
contains 2–4 anchoring villi and
their branches.
One anchoring villus and its
ramifications (ramus chorii,
ramuli chorii and floating villi)
constitute a fetal cotyledon.
Measurements of placenta at full term:
• Diameter: 15–20 cm
• Thickness: 3 cm
• Weight: 500 g.
Structure Of Placenta :
Maternal side—basal plate
Stratum spongiosum of decidua basalis
containing maternal blood vessels
 – Outer layer of syncytiotrophoblast
(Nitabuch’s layer)
 – Outer shell of cytotrophoblast
 – Inner layer of syncytiotrophoblast
(Rohr’s fibrinoid stria).
Fetal side—chorionic plate
– Covered by amnion
 – Primary mesoderm with fetal blood
vessels
 – Cytotrophoblast

Between basal plate and chorionic
plate
 – Intervillous space
 - Volume—140 mL
 - Maternal blood passing through
intervillous space—500 mL/minute
 - Volume of fetal blood flowing
through fetal villi—400 mL/minute.
– Stem villi—primary, secondary,
tertiary
Placental Membrane/Barrier

 In the placenta, maternal blood circulates through the intervillous

space and fetal blood circulates through blood vessels in the villi.
 flow side by side and in opposite directions they do not mix with each
other.
They are separated by a membrane, made up of the layers of the
wall of the villus.
Tissues intervening between fetal blood in chorionic villi and
maternal blood in intervillous space constitute the placental
membrane or barrier.
All interchanges of oxygen, nutrition and waste products take place
through this membrane.
The constituent structures forming the
placental barrier or maternal fetal barrier
extending from the maternal erythrocyte to
fetal erythrocyte are as follows: –
 In the early part of pregnancy, the barrier
presents the following layers :
 Endothelium of fetal blood vessels, and its
basement membrane –
 Surrounding mesoderm (connective tissue) –
 Cytotrophoblast and its basement membrane
 - Syncytiotrophoblast.
In the later part of pregnancy, the efficiency of
the membrane is increased due to the
reduction in its thickness by
 - Disappearance of cytotrophoblast
 - Thinning of syncytiotrophoblast
 - Edematous stroma
 - Peripheral migration of fetal blood vessels
 - It presents endothelium of fetal capillaries
resting on basement membrane and
syncytiotrophoblast only.
The total area of this membrane varies from 4 m2 to 14 m2 .
 As in the gut, the effective absorptive area is greatly increased by the
presence of numerous microvilli on the surface of the
syncytiotrophoblast.
 This membrane, which is at first 0.025 mm thick, is reduced to 0.002
mm.
However, toward the end of pregnancy, a fibrinoid deposit appears on
the membrane, and this reduces its efficiency.

FUNCTIONS OF PLACENTA :
 It acts as a temporary organ that allows transport of oxygen, water,
electrolytes and nutrients (in the form of carbohydrates, lipids,
polypeptides, amino acids and vitamins) from maternal to fetal blood
and thus maintains the nutrition of the fetus. A full term fetus takes up
about 25 mL of oxygen per minute from maternal blood. short
It eliminates excretion of carbon dioxide, urea and other waste products produced by the
fetus into the maternal blood.
 Maternal antibodies [immunoglobulin G (IgG), gamma globulins or immunoglobulins]
reaching the fetus through the placenta give the fetus immunity against some infections
(e.g. diphtheria and measles).
The placenta acts as a barrier and prevents many bacteria and other harmful substances
from reaching the fetus.----
• However, most viruses (including poliomyelitis, measles and rubella) and some bacteria can pass across it.
• Drugs taken by the mother may also enter the fetal circulation and can produce congenital malformations.
• As a rule, maternal hormones do not reach the fetus.
• However, synthetic progestins and synthetic estrogens (e.g. diethylstilboestrol) easily cross the placenta and can have adverse effects on
the fetus (including carcinoma in later life).
While permitting the exchange of several substances between the maternal and fetal
blood, it keeps these blood streams separate, thereby preventing antigenic reactions
between them.
The placenta synthesizes several hormones----These are probably produced in the
syncytiotrophoblast---- Progesterone secreted by the placenta is essential for
maintenance of pregnancy after the 4th month
Estrogens (mainly estriol) produced by the placenta reach maternal blood and
 CLASSIFICATION OF
PLACENTA
1. Based on shape :
Discoid—round or disc like
 Bidiscoidal—it consists of two discs
 Oval
 Triangular
 Irregular
 Lobed—it divides into lobes
 Diffuse/placenta membranacea —
chorionic villi persists all-round the
blastocyst
 Placenta succenturiata --a small part of (A) Discoid; (B) Bidiscoidal; (C) Oval; (D) Triangular; (E)
the placenta is separated from the rest of it Irregular; (F) Lobed—it divides into lobes; (G) Diffuse
 Fenestrated —presence of hole or or placenta membranacea; (H) Placenta Succenturiata;
opening in the placenta (I) Fenestrated; (J) Circumvallate
 Circumvallate —when peripheral edge of
placenta is covered by a circular fold of
decidua, it is called circumvallate.
2. According to attachment
of umbilical cord
 Normal—Central
insertion
Paracentral insertion of
umbilical cord
 Marginal or battledore (A) Normal; (B) Paracentral insertion of umbilical cord; (C) Marginal
placenta —Cord is or Battledore placenta; (D) Velamentous
attached to the margin of
placenta
 Velamentous —
Umbilical cord is attached
to the fetal membrane
close to the peripheral
margin of placenta.
3. According to
distribution of
umbilical arteries:
 Disperse type —
Umbilical arteries
show dichotomous
branching and show
progressive
reduction in size Magistral type Furcate
 Magistral type —
Arteries present
uniform caliber up to
the periphery of
placenta Disperse type
 Furcate —Blood
vessels divide
before reaching the
placenta.
4. Phylogenetic classification:
According to tissues from
maternal and fetal parts of
placenta contributing for
placental barrier
 CLINICAL CORRELATIONS FOR PLACENTA
Anatomical variations:
Variant morphologies of the placenta are frequently encountered, such as is the case
of a bilobed placenta where this organ is separated into two near equal-sized
lobes.
The estimated incidence of this specific variation is at up to ~4% of pregnancies.
It can be associated with some complications such as first-trimester bleeding.
Placenta disorders:
Besides the developmental abnormalities referred above, the placenta may also
be affected by a number of medical conditions.
An example of these disorders is a condition known as placenta previa:
implantation of the placenta over the cervical os.
This condition usually presents as painless vaginal bleeding in the third trimester.
In these cases, mother and fetus need careful monitoring and delivery is often by
cesarean section.
Placental Abruption:
 is when a part, or all of, the placenta
separates prematurely from the uterine
wall and is an important cause
of antepartum haemorrhage.

 It occurs following a rupture of maternal

vessels within the basal layer of the
endometrium. Blood accumulates and
causes the placenta to split from the
basal layer. The detached portion is
unable to function which can lead to rapid
foetal compromise.

 Important risk factors for this

include: previous placental
abruption, pre-eclampsia, abnormal lie
of the foetus, polyhydramnios,
smoking, multiple pregnancy,
underlying thrombophilia and
abdominal trauma. The most predictive
factor is a placental abruption in a
Women usually present with painful vaginal bleeding during their
pregnancy. On examination the uterus may be woody (tense) and painful
on palpation.
Management of placental abruption should consist of:
CTG(cardiotocograghy) to assess/monitor foetal wellbeing if the
woman is past 26 weeks gestation
Give anti-D within 72 hours of the onset of bleeding if the woman is
rhesus D negative
Emergency delivery/Induction of labour/Conservative management and
monitoring of the foetus depending on the degree of foetal distress
present and the health of the mother
 Clinical correlation
Amniotic fluid
 Amniotic fluid: It is a clear, watery fluid (98%) and contains 2% solids (inorganic salts, urea,
proteins, sugars).
 Source: Fetal/maternal/both ◆ maternal plasma, Amnion, fetal kidney, fetal lung, placenta
◆ Amnio-fetomaternal exchange
 Amount ◆ 10th–20th week: 25–400 mL ◆ Increases up to 6th month, then decreases. At 28 weeks, it is
800 mL and at term it is 400 mL
 Abnormal production ◆ Hydramnios—more than 2 L of amniotic fluid will be present. In some cases,
hydramnios is associated with, which prevents swallowing of amniotic fluid by the fetus atresia of the
esophagus
◆ Oligoamnios—scanty amniotic fluid----It is sometimes associated with renal agenesis, as no urine is
added to the amniotic fluid----Both conditions can cause abnormalities in the fetus.-----They can also
cause difficulties during childbirth.
Clinical importance of amniotic fluid:
Amniocentesis: It is a technique to collect amniotic fluid. The fluid is collected either through cervix or
anterior abdominal wall. This procedure is usually done during 15–20 weeks of pregnancy. There is risk
of fetal injury or preterm delivery in performing this procedure
The indications for this procedure are:
 Maternal age
 Bad obstetric history
 Cytogenetic analysis:
Diagnosis of trisomy’s, sex-linked disorders
 Biochemical analysis: Enzyme estimations—gross fetal anomalies—
alpha-fetoproteins, surfactant
 Metabolic disorders: – Lipid—Tay-Sachs disease –
Mucopolysacharides—Hurler’s syndrome – Carbohydrate—Pompe’s
disease – Purine—Lesch-Nyhan syndrome
 Amniotic stem cells: Production of embryonic cells in stem cell therapy
for defects of mesenchymal, hematopoietic, neural, epithelial or
endothelial cell origin.
Amniotic bands syndrome :
 known as constriction ring syndrome,
happens when fibrous bands of the amniotic
sac (the lining inside the uterus that contains
a fetus) get tangled around a developing
fetus
 In rare cases, the bands wrap around the
fetus’ head or umbilical cord. Most of the
time, the bands wrap around an arm, leg,
fingers, or toes.
 This can cause serious constrictions
(tightening), acting like a tight rubber band
around the body part.
 Most children with amniotic band syndrome
will have bands on more than one part of
the body
 Amputation of limb, ring like
constrictions of limb, other abnormalities
including craniofacial malformations can
occur.
 This condition results from infections or
toxins affecting the fetus or fetal
 Umbilical cord
As the ventral body wall closes in, the yolk
stalk and allantois are brought together, along
with their mesodermal sheaths and blood
vessels.
 Enclosing everything is a wrapping of amnion.
 In this manner a cylindrical structure, the
umbilical cord, comes to connect the embryo
with the placenta.
 It will serve the embryo and fetus as a
physiological lifeline throughout the pregnancy.
The mature cord is about 1.3 cm (0.5 inch)
in diameter, and it attains an average length of
nearly 50 cm (1.6 feet).
 Components of umbilical cord vary with
gestational age of the fetus
The umbilical cord is a connection
between the mother’s and fetus’
system.
 It contains one vein and two
arteries, which help carry out the to-
and-fro of nutrients and oxygen
between the mother’s and the baby’s
systems.
It contains two smaller arteries,
which carry blood from the fetus to
the placenta, and one larger vein,
which carries blood to the fetus
from the placenta.
The cord is clamped and cut by
the doctors after birth, and the
remaining umbilical stump dries and
falls off.
The point where the umbilical cord
was connected to baby until birth