The human placenta is discoid, haemochorial, deciduate, and larynthine. It attaches to the uterine wall and connects the mother and fetus through the umbilical cord. The placenta undergoes development from implantation through the third trimester, forming the chorionic and basal plates separated by the intervillous space containing branching villi. The placenta acts as the site of nutrient, waste, and gas exchange between mother and fetus as well as producing important hormones. Various abnormalities can occur in placental shape, implantation, circulation or development that impact clinical outcomes.

1. DR. SNIGDHA KUMARI
SENIOR RESIDENT
ESIC-PGIMSR, KOLKATA

2.  The human placenta is -
 discoid
 haemochorial
 deciduate
 larynthine
The placenta is attached to the uterine wall and
establishes connection between the mother and fetus
through the umbilical cord.

3.  Fetal component– from chorion frondosum
 Maternal component – from decidua basalis

4.  Interstitial implantation completed on 11th day.
 The blastocyst is surrounded on all sides by lacunar spaces
around cords of syncytial cells , called trabeculae.

5. On 13th day
- Stem villi developes from trabeculae .
- Stem villi connect the chorionic plate with the basal
plate.
- Primary, secondary and tertiary villi are successively
developed from stem villi.
On 21st day
- Arterio-capillary-venous system in the mesenchymal
core of each villus is completed.

12.  At 3rd to 4th week lacunar spaces become confluent
and form multilocular receptacle lined by
syncytium and filled with maternal blood.
 This space becomes future intervillous space.

13. This is the
endometrium of the
gravid (pregnant)
uterus.
 It has four parts:
 Decidua basalis
 Decidua capsularis
 Decidua parietalis
 Decidua reflexa
13

14.  Until the beginning of the
8th week, the entire
chorionic sac is covered
with villi.
 After that, as the sac grows,
only the part that is
associated with Decidua
basalis retain its villi.
 Villi of Decidua capsularis
compressed by the
developing sac.
 Thus, two types of chorion
are formed:
 Chorion frondosum
(villous chorion)
 Chorion laeve – bare
(smooth) chorion
 About 18 weeks old, it
covers 15-30% of the
decidua and weights
about 1 6 of fetus
14

15.  The villous chorion
( increase in
number, enlarge and
branch ) will form
the fetal part of the
placenta.
 The decidua basalis
will form the
maternal part of
the placenta.
 The placenta will
grow rapidly.
 By the end of the 4th
month, the decidua
basalis is almost
entirely replaced by
the fetal part of the
placenta.
15

16. GROWTH OF THE PLACENTA
Upto 16th wk the placenta grows both
in thickness and circumference , after that there is little
increase in thickness but it increases circumferentially
till term.

17.  Covered by smooth glistening amnion with the
umbilical cord attached at or near centre.
 At term about four –fifths of the placenta is of fetal
origin.

18.  Rough and spongy.
 Maternal blood gives it a dull red colour.
 It is mapped out into 15 to 20 somewhat convex
polygonal areas known as lobes or cotyledons
which are limited by fissures.
 Only the decidua basalis and the blood in the
intervillous space are of maternal in origin.

20.  The placenta consists of two plates—
1. The chorionic plate lies internally and lined by amniotic
membrane. The umbilical cord is attached to this plate.
2. The basal plate lies to the maternal aspect.
 Between the two plates lies the intervillous space
containing the stem villi and their branches , the space
being filled with maternal blood.

21.  From within outwards it consists of –
i. Primitive mesenchymal tissue containing branches of
umbilical vessels
ii. A layer of cytotrophoblast and
iii. Syncytiotrophoblast.
 The stem villi arise from the plate.
 It forms the inner boundary of choriodecidual space.

22.  It consists of the following structures from outside inwards--
i. Part of the compact and spongy layer of the decidua basalis
ii. Nitabuch’s layer of fibrinoid degeneration of the outer
Syncytiotrophoblast at the junction of the cytotrophoblastic
shell and decidua.
iii. cytotrophoblastic shell
iv. Syncytiotrophoblast
 Perforated by the spiral branches of the uterine vessels
through which the maternal blood flows into the intervillous
space.

24.  Bounded on the inner side by the chorionic plate and
the other side by the basal plate , limited on the
periphery by the fusion of the two plates.
 Lined internally on all sides by the Syncytiotrophoblast
and is filled with slow flowing maternal blood.
 Numerous branching villi which arise from the stem
villi project into the space and constitute chief content
of the intervillous space.

25.  Arise from chorion plate and extends to the basal plate.
 With progressive development primary, secondary and tertiary
villi are formed.
 Functional unit of placenta (fetal cotyledon or placentome)
derived from a major stem villus.
 Functional subunit (lobule)derived from a tertiary stem villi.
 The total villi surface, for exchange , approx. varies between 10 to
14 sqms.
 The fetal capillary system within the villi is almost 50 km long.
 Blood vessels within the branching villi do not anastomose with
the neighbouring one.

27. IN THE EARLY PLACENTA
Each terminal villus has got the following structure
from outside inwards
1. Outer Syncytiotrophoblast
2. Cytotrophoblast
3. Basement membrane
4. Central stroma containing fetal capillaries, primitive
mesenchymal cells , connective tissue and a few
phagocytic cells.

28. Normal Placenta (At term)
Diameter : 15 to 22 cm
Thickness : 2.0 ~ 2.5 cm
Weights : approximately 500 g (about 1 lb)
Placental and fetal size and weight roughly correlate in
a linear fashion.
Fetal growth depends on placental weight which is less
with small for gestational age infants
-Heinonen and colleagues, 2001-

29.  Placenta separates after the birth of the baby and the
line of separation is through the decidua spongiosum.

30.  Placental circulation consists of independent circulation of
blood in two systems:
1. Utero-placental circulation
2. Feto-placental circulation
 A mature placenta has a volume of about 500ml of
blood ,350ml being occupied in the villi system and 150 ml
lying in the intervillous space.
 The blood of the intervillous spaces is replenished about 3
or 4 times per minute.

31.  Blood in the intervillous space is temporarily outside maternal
circulatory system.
 It enters the intervillous space through 80 to 100 spiral
endometrial arteries in the decidua basalis.
 These vessels discharge into the intervillous space through gaps
in the cytotrophoblastic shell.
 Blood flowing from spiral arteries is pulsatile and is propelled in
jet-like fountains by the maternal blood pressure.
 Welfare of the embryo and fetus chiefly depends on adequate
bathing of branch villi with maternal blood.
 Reduction in utero-placental circulation result in fetal hypoxia
and IUGR.

32.  Poorly oxygenated blood leaves fetus and passes through
umbilical arteries to the placenta.
 At the site of attachment of cord to placenta, these arteries
divide into number of radially disposed chorionic arteries
that branch freely in chorionic plate before entering
chorionic villi.
 Blood vessels form extensive arterio-capillary-venous
system within chorionic villi, brings fetal blood extremely
close to maternal blood.

34.  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.

35.  Development of uteroplacental vessels proceeds in two waves or
stages.
i. First wave occurs before 12 wks. post- fertilization and consists
of invasion and modification of spiral arteries up to border
between deciduas and myometrium.
ii. Second wave between 12 and 16 wks. involves some invasion of
the intramyometrial segments of spiral arteries.
 Remodeling by this two-phase invasion converts narrow-lumen,
muscular spiral arteries into dilated, low-resistance uteroplacental
vessels.

37.  Partition between fetal & maternal circulation.
 Not a perfect barrier.
 Thickness- ~0.025mm
 In early pregnancy it consists of--
1. Syncytiotrophoblast
2. Cytotrophoblast
3. Basement membrane
4. Stromal tissue
5. Endothelium of the fetal capillary wall with its
basement membrane.

39. PLACENTAL BARRIER AT TERM
 Sparse cytotrophoblast & distended fetal capillaries almost fill
the villus.
 Attenuation of syncytial layer.
 Thin ‘alpha zones’ also known as vasculo-syncitial membrane,
where syncytiotrophoblast is thin & anuclear are for gas
exchange.
 Thick ‘beta zones’ with the layer remaining thick in patches
containing extensive ER are for hormone synthesis.

40.  Increase thickness of villus membrane found in IUGR &
cigarette smokers.
 Basement membrane becomes thicker.
 Stroma contains dilated vessels along with all the
constitute & few Hofbauer cells .

42.  – Placental transfer
 – Metabolism
 – Hormone production
 – Haematopoietic
 – Immunological

43.  RESPIRATORY--
Gaseous exchange [CO2, O2]
– Passive diffusion across a pressure gradient
– assisted by maternal hyperventilation [progesterone
effect] & fetal haemoglobin.
Oxygen supply to the fetus @ 8ml/kg/min is achieved
with cord blood flow of 165-330 ml/min.

44.  EXCRETORY
Waste products from fetus such as urea, uric acid &
creatinine are excreted in maternal blood by simple
diffusion.
 NUTRITIVE
Glucose - facilitated diffusion
Lipids - triglycerides & fatty acids directly transported
from mother to fetus.
Amino acids - active transport (amino acid
concentration is higher in fetal blood than in maternal
blood)

45.  WATER AND ELECTROLYTES
Na, K, Cl - simple diffusion
Ca, P, Fe - active transport
Water soluble vitamins - active transport
Fat soluble vitamins - slow transfer (remains at
low level in fetal blood)

46.  HORMONES
 Insulin
 Adrenal steroids
 Thyroid hormones
 Chorionic gonadotrophin or placental lactogen
cross the placenta at a very slow rate to keep the fetal
plasma concentration low.
 Parathormone
 Calcitonin
does not cross the placenta.

47.  Rate of metabolism similar to adult liver or kidney.
 Oxygen consumption is of same order as that of
pancreas and kidney.
 Metabolic processes include: active glycolytic cycle,
pentose phosphate pathway, tricarboxylic cycle,
electron transmitter systems.
 More than 60 placental enzymes have been described.

48.  Diamine oxidase – inactivates the circulatory pressure
amines.
 Oxytocinase – neutralises the oxytocin
 Phospholipase A2 - arachidonic acid synthesis.

49. Protein [polypeptides] Hormones
1. Human Chorionic Gonadotrophin –
- rises in 1st-early 2nd trimester, low levels after ~16 wks
- responsible for fetal adrenal cortex development
2. Human Chorionic Somatotrophin –
- fosters embryonic development by increasing fetal cell
glucose absorption and stimulating lipid and CHO
metabolism.

50. 3. Human Placental Lactogen –
- rises progressively from ~12 wks upto term
- possibly useful in preparation for lactation
- contributes to diabetogenic effects of pregnancy
4. ACTH, TSH, Melanocyte Stimulating Hormone,
Relaxin, Oxytocin, Vasopressin –
All isolated from placental tissue but most likely are of
maternal or fetal origin.

51. All rise progressively to plateau at term
1. Progesterone – Maintains pregnancy
Maintains uterine quiesence
↑ mammary growth
Antialdosterone effect
2.Oestrogens (oestriol) –↑ uterine growth & vascular supply to
decidua & myometrium
- ↑ metabolism & placental enzyme systems.
3. Androgens
4. Corticosteroids

52.  Placenta takes up Fe, Vit. B12 & Folic acid tendency
towards anaemia in pregnancy.
 Fetal erythropoietin may cross placenta to mother since
maternal reticulocyte counts are elevated in presence of fetal
anaemia.

53.  Feto-placental unit is an allograft that defies the
foreign body tissue reaction. [Type IV cell-mediated
reaction]
 Fetus not antigenically mature.

54.  Abnormal Shape or Implantation
 Degenerative Placental Lesions
 Circulatory Disturbances
 Hypertropic Placental Abnormalities
 Tumors of the Placenta

55. - Multiple placentas with a single fetus
placenta bipartita or bilobata
placenta duplex, triplex
- succenturiate lobes
- membranaceous placenta
- ring – shaped placenta
- fenestrated placenta
- placenta accreta, increta & percreta
- extrachorial placentation
circumvallate placenta
circummarginate placenta

56. Abnormality Definition Clinical significance
Multiple
Placentas with a
single fetus
 Placenta bipartita or bilobata
- The placenta is separated into
lobes
- Division is incomplete and the
vessels of fetal origin extend from
one lobe to the other before
uniting to
form the umbilical cord
 Placenta duplex, triplex
- Two or three distinct lobes are
separated entirely and the vessels
remain distinct.
Bilobed Placenta
Succenturiate
lobes - Small accessory lobe ≥1, develop
in the membranes at a distant from the
periphery of the main placenta, to
which they usually have vascular
connections of fetal origin
- Retained in the uterus
after delivery and may
cause serious hemorrhage
- Accompanying vasa
previa dangerous fetal

57. Abnormality Definition Clinical significance
Membranaceous Placenta
or
Placenta Diffusa
- All of the fetal membranes
are
covered by functioning
villi and the
placental develops as a
thin
membranous structure
occupying
the entire periphery of the
chorion
- Serious hemorrhage d/t
associated placenta
previa or accreta
Ring – shaped Placenta
- Placenta is annular in
shape and sometimes a
complete ring of placental
tissue
- Variant of membraceous
placenta
- Tissue atrophy in a
portion of the ring a horseshoe
shape in more common
- Antepartum &
postpartum bleeding and
fetal growth restriction

58. Diagnosis Definition Clinical significance
Fenestrated Placenta
- Central portion of a
discoidal placenta is
missing
- In some instances, there is
an actual hole in the placenta
but more often the defect
involves only villous tissue
with the chorionic plate intact
- Mistakenly
considered to indicate
that a missing portion
of placenta
Placenta
Accreta
Increta
Percreta
- Serious variations in
which trohpoblastic tissue
invade the myometrium to
varying depths
- Much more likely with
placenta previa or with
implantation over a prior
uterine incision or perforation
- Torrential hemorrhage

60. Abnormality Definition Clinical significance
Extrachorial
Placentation
 Circumvallate
Placenta
Circummarginate
placenta
- When the chorionic plate, which is on
the fetal side of the placenta, is smaller
than the basal plate, which is located
on the maternal side, the placental
periphery is uncovered
- Fetal surface of such a placenta
presents a central depression
surrounded by a thickened, grayish-
white ring.
- Ring : composed of a double fold of
amnion and chorion with degenerated
decidua and fibrin in between
- Within the ring, the fetal surface
present the usual appearance, except that
the large vessels terminate abruptly at
the margin of the ring
- Ring dose not have the central
depression with the fold of membranes
- Antepartum
hemorrhage
from placental
abruption
and fetal hemorrhage
- Preterm delivery
- Perinatal mortaliy
- Fetal malformations
- Less well defined

61.  Causes : Trophoblast aging or impairment of
uteroplacental circulation with infarction.
 Deposition of calcium salts is heaviest on the maternal
surface in the basal plate –
→ further deposition occurs along the septa and both
increase as pregnancy progresses.
 Diagnosis : Sonography

63. - Placental Infarctions
- Maternal Floor Infarction
- Placental Vessel Thrombosis

64.  Skriking enlargement of the chorionic villi is
commonly seen in association with
Severe erythroblastosis
Fetal hydrops
Maternal diabetes
Fetal CHF
Maternal-fetal syphilis

65.  Gestational Trophoblastic Disease
 Chorioangioma (hemangioma)
 Tumours metastatic to the Placenta
 Embolic Fetal Brain Tissue

67.  At term amnion is a tough, tenacious & pliable
membrane.
 Innermost avascular fetal membrane.
 Contiguous with amnionic fluid.
 Provides almost all tensile strength.
 Lacks smooth muscle cells, nerves, lymphatics & blood vessels.

68.  Bourne (1962) described five separate layers of amnion –
- innermost single layer of cuboidal epithelium derived from
embryonic ectoderm.
- basement membrane
- acellular compact layer, which is composed primarily of
interstitial collagens
- fibroblast-like mesenchymal cells, derived from embryonic
disc mesoderm
- acellular zona spongiosa, contiguous with second fetal
membrane, the chorion laeve

70.  Early during implantation, a space develops between the
embryonic cell mass and adjacent trophoblasts.
 Small cells that line this inner surface of trophoblasts have been
called amniogenic cells—precursors of amnionic epithelium.
 The amnion is first identifiable about the seventh or eighth day
of embryo development. It is initially a minute vesicle, which
then develops into a small sac that covers the dorsal surface of
the embryo.
 As the amnion enlarges, it gradually engulfs the growing embryo,
which prolapses into its cavity.

72.  Reflected amnion is fused to the chorion laeve.
 Placental amnion covers placental surface & thereby is in
contact with adventitial surface of chorionic vessels.
 Umbilical amnion covers the umbilical cord.
 In the conjoined portion of membranes of diamniotic-
dichorionic twin placenta, fused amnions are separated by
fused chorion laeve.
 With diamniotic-monochorionic placenta, there is no
intervening tissue between the fused amnions.

73.  Meconium Staining
 Chorioamnionitis
 Other Abnormalities

74. Abnormalities Definition & causes Clinical significance
Amnionic cyst
 Lined by typical amnionic
epithelium
 Fusion of amnionic folds with
subsequent fluid retention
Amnion nodosum
 Tiny, creamy nodules in the
amnion made up of vernix caseosa
with hair, degenerated squames and
sebum
 Oligohydramnios
Found in
 fetuses with renal agenesis
 Prolonged preterm ruptured
Membranes
 The placenta of the donor
fetus with twin-to-twin
transfusion syndrome
Amnionic band  Caused when disruption of the
amnion
leads to formation of bands or
strings
that entrap the fetus and impair
growth
and development of the involve
structure
 Intrauterine amputation

75.  Cord develops in yolk sac & umbilical vesicle which are
prominent early in pregnancy.
 Embryo, at first, is a flattened disc interposed between
amnion & yolk sac.
 Its dorsal surface grows faster than the ventral surface.
 Embryo bulges into amnionic sac in association with
elongation of neural tube.
 Dorsal part of yolk sac is incorporated into the body of
embryo to form gut.

76.  Allantois projects into base of body stalk from the caudal
wall of the yolk sac & later, forms anterior wall of hindgut.
 As pregnancy advances, yolk sac becomes smaller & its
pedicle relatively longer.
 By about middle of 3rd month, expanding amnion
obliterates exocoelom, fuses with the chorion laeve, &
covers the bulging placental disc & lateral surface of the
body stalk.
 Latter is then called the umbilical cord—or funis.

78.  It normally has two arteries and one vein .
 Right umbilical vein disappears early during fetal
development, leaving only the left vein.
 Intra-abdominal portion of duct of umbilical vesicle,
extending from umbilicus to intestine, usually atrophies &
disappears.
 If patent, it is known as Meckel’s diverticulum.
 Most common vascular anomaly - absence of one umbilical
artery which may be associated with fetal anomalies .

80.  Umbilical cord, or funis, extends from fetal umbilicus
to fetal surface of placenta or chorionic plate.
 Exterior is dull white, moist, & covered with amnion,
through which three umbilical vessels may be seen.
 Diameter - 0.8 to 2.0 cm.
 Average length of 55 cm with a range of 30 to 100 cm.
 Generally, cord length less than 30 cm is considered
abnormally short.

81.  Folding and tortuosity of vessels, which are longer
than cord itself, frequently create nodulations on the
surface, or false knots, which are essentially varices.
 The extracellular matrix is a specialized connective
tissue referred to as Wharton’s jelly.
 Two arteries are smaller in diameter than the vein.

82.  Length
 Cord Coiling
 Single Umbilical Artery
 Four-vessel cord
 Abnormalities of cord insertion
 Cord Abnormalities capable of impeding
blood flow
 Hematoma
 Cysts

83. Appreciable variation, extremes range –
 No cord(acordia) ~ lengths up to 300cm
 Excessively long cords : ≥ 70cm ( ≥2 SD )

84.  Short umbilical cord
Adverse perinatal outcomes –
-fetal growth restriction
- congenital malformations
- intrapartum distress & risk of death (doubled)
(Krakowiak and associates,2004)
 Excessively long cord
Associated with
-maternal systemic disease
-delivery complications -cord prolapse, cord entanglement
-fetal anomalies and respiratory distress
Perinatal mortality : ↑ nearly threefold

85.  Umbilical vessels: in a spiraled manner
 Hypocoiled cords
- ↑ in various adverse outcome in fetuses
- meconium staining, preterm birth and fetal distress
 Hypercoiled cords
- higher incidence of preterm delivery & cocaine
abuse
- Rana and associates (1995)

86.  Umbilical cord –2 arteries
- 1 vein
 Risk factors –
↑ incidence in women with GDM, PIH, APH, epilepsy,
oligohydramnios & hydramnios.
 ¼ of all infants with only 1 artery have associated
congenital anomalies.

87.  Diagnosis - routine ultrasound screening
 Prognosis - depends on whether 2 vessel cord is
associated with other abnormalities
or
whether it is an isolated finding
 When a 2 vessel cord is an isolated finding
aneuploid ≥ ½
Renal aplasia, Limb-reduction defects, Atresia of hollow organs
in such fetuses, suggesting a vascular etiology
 Growth restriction did not occur in anatomically normal
fetus with a single artery
Goldkrand and associates (2001)

88.  Venous remnant in 5%
 Significance : unknown

89. Usually inserted at or near center of fetal surface of placenta
 Furcate insertion
 Marginal insertion
 Velamentous insertion
 Vasa previa

90. Abnormalities Definition Incidence Significance
Furcate insertion
Umbilical vessels separate
from the cord substance before
their insertion into the
placenta
Rare
Prone to twisting &
thromboses as vessels
lose their cushioning
Marginal Inserion
Battledore placenta:
Cord insertion at the placental
margin
7% at term
Cord being pulled off
during delivery of
the placenta
Velamentous
Insertion Umbilical vessels separate in
the membranes at a distance
from the placental margin
Reach surrounded only by a
fold of amnion
1.1%
More frequently
with twins
28% of triples

92.  Associated with velamentous insertion when some of
the fetal vessels in the membranes cross the region of
the cervical os below the presenting fetal part
 Associated with
- Velamentous insertion (50%)
- Marginal cord insertion
- Bilobed or Succenturiate-lobed placentas (50%)
 Risk factors
- Bilobed , Succenturiate or low-lying placenta
(80%)
- Multifetal pregnancy
- Pregnancy resulting from in vitro fertilization

93.  Diagnosis
- Color Doppler examination
Perinatal diagnosis : associated with increased survival
Antenatal diagnosis : associated with decreased fetal mortality
compared with discovery at delivery
 Antepartum or intrapartum haemorrhage
 Detecting fetal blood
- Apt test
- Wright stain : smear the blood on glass slides
stain the smears with Wright stain and
examine for nucleated RBC
: normally are present in cord blood but
not maternal blood