Download MBBS (Bachelor of Medicine, Bachelor of Surgery) Obstetrics and Gynaecology PPT 1 Placenta Lecture Notes
Placenta
OBSTETRICS AND GYNAECOLOGY
1. Discuss anatomy, function and abnormalities
related to placenta.
2. Explain abnormalities related to length of
cord.
? Placenta is a remarkable organ
? Has a relative short life span, it undergoes rapid
growth ,differentiation and maturation.
? A unique fetal ?maternal communication
system which creates a hormonal environment
that helps initially to maintain pregnancy and
eventually initiates the events leading to
parturition
The human placenta is:
? Discoid
? Hemochorial
? Deciduate
Development of placenta-
Two sources
? Fetal ? chorion Frondosum
? Maternal- decidua basalis
PLACENTA AT TERM:
Placenta is a discoid organ
15 ? 20cm in diameter
3cm Thick at center
Weighs about 500gms
Placental membrane
Total area-4 to 14 sq m
Similar to absorbtive area in adult git
In later part of pregnancy the membrane
thickness reduces from 0.025mm to0.002mm
Is classified as haemochorial
PLACENTAL BARRIER
?
Inspite of close proximity , there is no mixing of the maternal
and fetal blood.
?
They are separated by placental membranes or barrier.
PLACENTAL
CIRCULATION
UTEROPLACENTAL
FETOPLACENTAL
CIRCULATION
CIRCULATION
UTEROPLACENTAL CIRCULATION
? It is concerned with the circulation of maternal
blood through the intervillous space.
? Divided in 3 parts
1. Arterial circulation
2. Venous drainage
3. Circulation in intervillous space
? Blood in the intervil ous space is temporarily outside
maternal circulatory system.
? These vessels discharge into the intervil ous space through
gaps in the cytotrophoblastic shel .
? Blood flowing from spiral arteries is pulsatile and is propel ed
in jet-like fountains by the maternal blood pressure.
? Welfare of the embryo and fetus chiefly depends on adequate
bathing of branch vil i with maternal blood.
? Reduction in utero-placental circulation result in fetal hypoxia
and IUGR.
Arterial circulation
? About 120-200 spiral arteries open into
intervillous space.
Spiral artery remodelling
? There is cytotrophoblastic invasion into the spiral
arteries upto the intradecidual portion within
12weeks of pregnancy.
? Endothilial and muscoelastic media is destroyed
and replaced by fibrinoid material
? There is secondary invasion of trophoblast between
12-16 weeks.
? It extends upto the radial arteries within the
myometrium.
? SPIRAL ARTERIES are remodled into large bore
UTEROPLACENTAL ARTERIES.
INTERVILLOUS HEMODYNAMICS
Volume of blood in mature placenta
500ml
Volume of blood in intervil ous space
150ml
Blood flow in intervil ous space
150ml
Pressure in intervil ous space
1) During uterine contraction
30-50mm Hg
2)During uterine relaxation
10-15mm Hg
Pressure in supplying uterine artery
70-80mm Hg
Pressure in draning uterine vein
8mm Hg
FETOPLACENTAL CIRCULATION
? Two umbilical arteries enter the chorionic plate
underneath the amnion, each supplying one half of
placenta.
? The arteries breakup into small branches which
enter the stems of chorionic villi.
? Each in turn divides the primary, secondary and
tertiary vessels of the corresponding villi.
? This system provides a very large area for
exchange of metabolic and gaseous products
between maternal and fetal blood streams.
? Well-oxygenated fetal blood in fetal capillaries
passes into thin walled veins.
? This follow chorionic arteries to site of
attachment of the umbilical cord, where they
converge to form umbilical vein.
? This large vessel carries oxygen-rich blood to
the fetus.
One (usual) or more smal lobes of placenta, size of
cotyledon, may be placed at varying distances from
the placental margin.
In cases of absence of communicating blood
vessels, it is called placenta spuria.
Incidence: 3%
If the succenturiate lobe is retained, fol owing
birth of the placenta, it may lead to:
1. Postpartum haemorrhage
2. Subinvolution
3. Uterine sepsis
4. Polyp formation
Whenever the diagnosis of missing lobe is made,
exploration of the uterus and removal of the lobe
under general anaesthesia is to be done.
The fetal surface is divided into a central depressed zone
surrounded by a thickened white ring which is usualy
complete.
Vessels radiate from the cord insertion as far as the
ring and then disappear from view.
The peripheral zone outside the ring is thicker
and the edge is elevated and rounded.
There is increased chance of:
Abortion
Antepartum haemorrhage FGR
baby
Preterm delivery
Retained placenta or membranes
? Encroachment of some part over the lower segment.
? Imperfect separation in the third stage.
? Chance of retained placenta is more and manual removal becomes difficult.
? These abnormalities are serious variations in which trophoblastic tissues invade the
myometrium to varying depths.
? They are much more likely with placenta previa or with implantation over a prior uterine
incision or perforation.
The condition is usually associated
? when the placenta is implanted in lower segment
(Placenta praevia)
or over the previously injured sites as in caesarean
section
?dilatation and curettage operation
? manual removal
?myomectomy
The diagnosis is only made
? during attempted manual removal when the plane
of cleavage between the placenta and uterine wall
cannot be made out.
? Ultrasound imaging, colour Doppler and MRI have all
been valuable in the diagnosis.
? Absence of decidua basalis
? Absence of Nitabuch's fibrinoid layer
? Varying degree of penetration of the villi into the
muscle bundle (increta) or upto the
? serosal layer(percreta).
? The risk includes hemorrhage, shock,infection and
rarely inversion of the uterus.
Abnormal length of cord
Short cord
Less than 20cm
1. Prevent descent of the presenting part
special y during labour
2. Separation of normal y situated placenta
3. Favour malpresentation
4. Acute inversion
5. Fetal growth restriction
6. Intrapartum distress
7. Failure of external version
8. Two fold risk of fetal death
Clinical Significance
? cord prolapse
? cord entanglement round the neck or the body
? True knot
? False knots
Battledore placenta
? The cord is attached to the margin of the placenta.
? If associated with low implantation of the placenta,
there is chance of cord compression in vaginal delivery
leading to fetal anoxia or even death; otherwise, it has
got little clinical significance.
Velamentous placenta
? The umbilical vessels spread within the membranes at
a distance from the placental margin, which they reach
surrounded only by a fold of amnion.
? Although their incidence is approximately 1 percent,
velamentous insertion develops in more commonly
with placenta previa and multifetal gestations.
If the leash of blood vessels happen to traverse through the
membranes overlying the internal os, infront of the presenting
part,the condition is called vasa praevia.
? In the presence of fetal bleeding, urgent delivery is
essential either vaginally or by caesarean section.
? The newborn's haemoglobin is estimated and if
necessary, blood transfusion be carried out.
? If the baby is dead, vaginal delivery is awaited.
Knots
False Knots
False knots appear as knobs protruding from the cord
surface and are focal redundancies of a vessel or Wharton
jelly, with no clinical significance.
This post was last modified on 07 April 2022