DR. SNIGDHA KUMARI SENIOR RESIDENT

ESIC-PGIMSR, KOLKATA

THE PLACENTA AND FETAL MEMBRANES

The human placenta is -discoid haemochorial deciduatelarynthine

The placenta is attached to the uterine wall and establishes connection between the mother and fetus through the umbilical cord.

Fetal component– from chorion frondosum Maternal component – from decidua basalis

DEVELOPMENT

Interstitial implantation completed on 11th day.The blastocyst is surrounded on all sides by

lacunar spaces around cords of syncytial cells , called trabeculae.

Implantation of the blastocyst

Occurs 6 or 7 days after fertilization

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.

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.

DECIDUA This is the endometrium of the gravid (pregnant) uterus.

It has four parts:

Decidua basalis

Decidua capsularis

Decidua parietalis

Decidua reflexa

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DEVELOPMENT OF PLACENTA 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

C0nt..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.

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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.

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.

FETAL SURFACE

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.

MATERNAL SURFACE

.

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.

From within outwards it consists of –

i. Primitive mesenchymal tissue containing branches of umbilical vessels

ii. A layer of cytotrophoblast andiii. Syncytiotrophoblast.

The stem villi arise from the plate. It forms the inner boundary of choriodecidual

space.

CHORIONIC PLATE

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.

BASAL PLATE

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.

INTERVILLOUS SPACE

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.

STEM VILLI

IN THE EARLY PLACENTA Each terminal villus has got the following

structure from outside inwards 1. Outer Syncytiotrophoblast 2. Cytotrophoblast3. Basement membrane4. Central stroma containing fetal capillaries,

primitive mesenchymal cells , connective tissue and a few phagocytic cells.

STRUCTURE OF A TERMINAL VILLUS

PLACENTA AT TERMNormal 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-

Placenta separates after the birth of the baby and the

line of separation is through the decidua spongiosum.

SEPARATION OF PLACENTA

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.

CIRCULATION OF THE PLACENTA

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.

MATERNAL PLACENTAL CIRCULATION

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.

FETAL PLACENTAL CIRCULATION

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.

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.

INVASION OF SPIRAL ARTERIES

Partition between fetal & maternal circulation. Not a perfect barrier.Thickness- ~0.025mmIn early pregnancy it consists of-- 1. Syncytiotrophoblast2. Cytotrophoblast3. Basement membrane 4. Stromal tissue5. Endothelium of the fetal capillary wall with its

basement membrane.

PLACENTAL BARRIER

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.

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 .

– Placental transfer– Metabolism– Hormone production– Haematopoietic– Immunological

FUNCTIONS OF THE PLACENTA

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.

Placental transfer

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)

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)

HORMONES

Insulin Adrenal steroids Thyroid hormonesChorionic gonadotrophin or placental

lactogen cross the placenta at a very slow rate to keep the fetal plasma concentration low.

Parathormone Calcitonindoes not cross the placenta.

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.

Placental metabolism

Diamine oxidase – inactivates the circulatory pressure amines.

Oxytocinase – neutralises the oxytocin

Phospholipase A2 - arachidonic acid synthesis.

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.

Placental hormonal production

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.

All rise progressively to plateau at term

1. Progesterone – Maintains pregnancy Maintains uterine quiesence mammary growth Antialdosterone effect2.Oestrogens (oestriol) – uterine growth & vascular supply to decidua & myometrium - metabolism & placental enzyme systems.3. Androgens4. Corticosteroids

Steroid Hormones

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.

Placental haematopoiesis

Feto-placental unit is an allograft that defies the

foreign body tissue reaction. [Type IV cell-mediated reaction]

Fetus not antigenically mature.

Placental immunology

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

PLACENTAL ABNORMALITIES

- Multiple placentas with a single fetusplacenta bipartita or bilobataplacenta duplex, triplex

- succenturiate lobes- membranaceous placenta- ring – shaped placenta- fenestrated placenta- placenta accreta, increta & percreta- extrachorial placentation

circumvallate placentacircummarginate placenta

Abnormal shape or implantation

Abnormality Definition Clinical significance

Multiple Pla-centas 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 unit-ing 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 pre-via dangerous fetal hemor-rhage at delivery

Abnormality Definition Clinical significance

Membranaceous Placentaor

Placenta Diffusa

- All of the fetal mem-branes are covered by functioning villi and the placental develops as a thin membranous structure oc-cupying 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 com-plete ring of placental tissue - Variant of membraceous placenta - Tissue atrophy in a por-tion of the ring a horseshoe shape in more common

- Antepartum & postpartum bleeding and fetal growth restriction

Diagnosis Definition Clinical significance

Fenestrated Placenta

- Central portion of a dis-coidal placenta is missing - In some instances, there is an actual hole in the placenta but more often the defect in-volves 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 in-vade the myometrium to vary-ing depths - Much more likely with placenta previa or with im-plantation over a prior uterine incision or perforation

- Torrential hemorrhage

Abnormalities of Placental invasion

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 hemor-rhage from placental abrup-tion and fetal hemorrhage - Preterm delivery - Perinatal mortaliy - Fetal malformations

- Less well defined

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

Degenerative placental lesions

Placental calcification

- Placental Infarctions

- Maternal Floor Infarction

- Placental Vessel Thrombosis

Circulatory disturbances

Skriking enlargement of the chorionic villi is commonly seen in association with

Severe erythroblastosis Fetal hydrops

Maternal diabetes Fetal CHF Maternal-fetal syphilis

Hypertrophic Lesions of Chorionic Villi

Gestational Trophoblastic Disease

Chorioangioma (hemangioma)

Tumours metastatic to the Placenta

Embolic Fetal Brain Tissue

Tumours of Placenta

CHORIOANGIOMA (HEMANGIOMA)

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.

THE AMNION

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

Structure

Layers of Amniotic membrane

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.

Development

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.

ANATOMY

Meconium Staining Chorioamnionitis Other Abnormalities

ABNORMALITIES OF THE MEMBRANES

Abnormalities Definition & causes Clinical significance

Amnionic cyst Lined by typical amnionic epithe-lium 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 am-nion leads to formation of bands or strings that entrap the fetus and impair growth and development of the involve structure

Intrauterine amputation

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.

DEVELOPMENT OF THE CORD

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.

Cont..

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 .

THE CORD AT TERM

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.

STRUCTURE OF THE CORD

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.

Length Cord Coiling Single Umbilical Artery Four-vessel cord Abnormalities of cord insertion Cord Abnormalities capable of

impeding blood flow Hematoma Cysts

UMBILICAL CORD ABNORMALITIES

Appreciable variation, extremes range – No cord(acordia) ~ lengths up to 300cm

Excessively long cords : ≥ 70cm ( ≥2 SD )

Length

Short umbilical cordAdverse perinatal outcomes – -fetal growth restriction

- congenital malformations - intrapartum distress & risk of death (doubled)

(Krakowiak and associates,2004)

Excessively long cordAssociated with

-maternal systemic disease -delivery complications -cord prolapse, cord entanglement -fetal anomalies and respiratory distress

Perinatal mortality : nearly threefold

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)

Cord coiling

Umbilical cord –2 arteries

- 1 veinRisk factors –

omen with GDM, PIH, APH, epilepsy, oligohydramnios & hydramnios.

¼ of all infants with only 1 artery have associated congenital anomalies.

Single umbilical artery

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 arteryGoldkrand and associates (2001)

Venous remnant in 5%

Significance : unknown

Four – vessel cord

Usually inserted at or near center of fetal surface of placenta

Furcate insertion

Marginal insertion

Velamentous insertion

Vasa previa

ABNORMALITIES OF CORD INSERTION

Abnormalities Definition Incidence Significance

Furcate insertion

Umbilical vessels separate from the cord substance before

their insertion into the pla-centa

RareProne to twisting &

thromboses as vessels lose their cushioning

Marginal Inserion Battledore placenta:

Cord insertion at the placental margin

7% at termCord being pulled off

during delivery of the placenta

Velamentous Inser-tion 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

Velamentous Insertion

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

VASA PREVIA

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

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