Fetal Membranes and Placenta

1. Fetal membranes and placenta
Dr. Faiza Munir Ch
Medical Officer
dr.faizamunirch@gmail.com

2. Development of the fetus
• The period from the beginning of the 9th week (3rd month) to the birth is
known as fetal period.
• It is characterized by maturation of tissue and organs and rapid growth of
the body.
• The length of the fetus is usually indicated as crown rump length(sitting
height)or as a crown heel length (standing height)these measurements are
expressed in cm and are correlated with the age of fetus in weeks or
months.
• Growth in length is particularly striking during the 3rd , 4th and 5th months,
while an increase in weight is most striking during the last 2 months of
gestation. In general the length of pregnancy is considered to be 280 days
or 40 weeks after the onset of last normal menstrual period (LNMP). Or
more accurately 266 days or 38 weeks after fertilization.

4. 3rd month:
• Head: 3rd month ½ CRL, 5th month 1/3rd CRL,
• Birth 1/4th CRL.
• Face: More human like
• Ear: develop properly
• Eyes: laterally  ventral aspect of face
• Limbs: lengthens
• Primary ossification center: bone formation 12 week.
• Herniation: intestinal loop 6th and 12th week.
• External genitals: sex determination through USG.
• Reflex activity.

6. 4th – 5th month:
• Lengthening: CRL 15cm
• Weight 500gram
• Hair appears
• Mother felt fetal movement.
6th month:
• Reddish appearance(because subcutaneous fats not develop)
• A fetus born in 6th month have difficulty surviving.
• Although several organ systems able to function, the respiratory system and
central nervous system have not differentiated sufficiently and coordination
between two system is not yet well established.

7. 7th _ 9th month:
• Weight gain 3000-3400 grams
• Respiratory and central nervous system well established.
• Subcutaneous fats develop.
• Can be delivered
• Most fetuses are born within 10-14days of calculated delivery date. If they are
born much earlier they are categorized as premature, if born later they are
categorized postmature.

8. Fetal membranes and
placenta

9. EarlyHumanDevelopment

10. EarlyHumanDevelopment

11. EarlyHumanDevelopment

12. EarlyHumanDevelopment

13. Embryo after folding
Head swelling
Cardiac swelling
Umbilical cord
Y.S
G
U
T

14. • The term fetal membrane is applied to those structures derived from
the blastocyst which do not contribute to the embryo.
The amnion,
the chorion,
the yolk sac
Allantois
Umbilical cord

15. Amnion
•Amniotic membrane :
amniotic epi. + extraembryonic
mesoderm
•Amniotic fluid:
Produce:1)amniotic cells
2) infusion of fluid from
maternal blood
3) urine output from the fetus
4) pulmonary secretions
Output: 1) absorbed by amniotic cells
2) fetus swallow

16. Amniotic Fluid
• Plays a major role in fetal growth and development.
• Daily contribution of fluid from respiratory tract is 300-400 ml.
• 500 ml of urine is added daily during the late pregnancy.
• Amniotic fluid volume is 30 ml at 10 weeks, 350 ml at 20 weeks,
700-1000 ml at 37 weeks.

17. Composition of AmnioticFluid
• 99 % is water
• Desquamated fetal epithelial cells
• Organic & inorganic salts
• Protein, carbohydrates, fats, enzymes, hormones
• Meconium & urine in the late stage
Abnormalities of amniotic fluid
• Oligo-hydramnios: the volume of the amniotic fluid is less than ½ litre. This may lead to
adhesions between the embryo and the amnion.
• Poly-hydramnios: the volume of the amniotic fluid is more than 2 litres. This may lead to
premature rupture of the amnion.

18. Significance of Amniotic Fluid
• Permits symmetrical external growth of the embryo and fetus
• Acts as a barrier to infection
• During labor it help dilatation of the cervix of the uterus and It wash birth canal and
protect the fetus against infections
• Prevents adherence of amnion to fetus
• Cushions & protects the embryo and fetus
• Helps maintain the body temperature
• Enables the fetus to move freely

19. Functions of amniotic fluid:
1- At early pregnancy:
1. Acts as water cushion that absorbs external shocks.
2. Acts as heat insulator.
3. Prevents adhesion of embryo to wall of uterus.
4. Prevents adhesion of fetal parts.
2- At late pregnancy:
1. A space for accumulated urine.
2. Allows fetal movements to help body muscles to develop.
3. Help suckling training and development of gut muscles.

20. 3- During labor:
1. Protects against uterine contractions.
2. Formation of bag of water that gradually dilate the
cervix.
3. Sterile amniotic washes vagina before passage of
baby.
4. Rupture of amniotic sac is a sign of start of delivery.

21. YolkSac
• It is large at 32 days
• Shrinks to 5mm pear shaped
remnant by 10th week &
connected to the midgut by a
narrow yolk stalk
• Becomes very small at
20 weeks
• Usually not visible thereafter
Primary yolk
sac
secondary yolk

22. Fate & development of yolk sac
• Primary yolk sac: It replaces cavity of blastocyst after the
formation of Heuser’s membrane which is formed of flat cells that
originate from hypoblast
cells at 9th& 10th day.
• Secondary yolk sac: additional cells from hypoblast cells will
line the Heuser’s membrane, reduction of size of yolk sac and
formation of allantois. This occurs in the 13thday.
• Defenitive yolk sac: During 3r
dweek, hypoblast become replaced by
endoderm. After folding, it shares in formation of gut and the part
remains outside the embryo is called defenitive yolk sac. It is
connected to yolk sac by vitello-intestinal duct.

23. SignificanceofYolkSac
• Has a role in transfer of nutrients during the 2nd and
3rd weeks
• Blood development first occurs here
• Incorporate into the endoderm of embryo as a
primordial gut
• Primordial germ cells appear in the endodermal lining
of the wall of the yolk sac in the 3rd week

24. FateofYolkSac
• At 10 weeks lies in the chorionic cavity between chorionic and amniotic sac
• Atrophies as pregnancy advances
• Sometimes it persists throughout the pregnancy but of no significance
• In about 2% of adults the proximal intra-abdominal part of yolk stalk persists
as an ileal diverticulum or Meckel diverticulum(congenital abnormality)

25. Allantois
• In the 3rd week it appears as a
sausagelike diverticulum from the
caudal wall of yolk sac that extends
into the connecting stalk
• During the 2nd month, the
extraembryonic part of the allantois
degenerates

26. Functionsof Allantois
• Blood formation occurs in the wall during the 3rd to 5th week
• blood vessels persist as the umbilical vein and arteries
• Becomes Urachus(fibrous remnant of allantois) and after birth is
transformed into median umbilical ligament extends from the apex of
the bladder to the umbilicus.

27. The Umbilical Cord
Anatomy
•Origin: it develops from
the connecting stalk.
•Length:
At term, it measures about
50 cm.
•Diameter: 2 cm.

28. Structure: It consists of mesodermal
connective tissue called Wharton's
jelly, covered by amnion.
It contains:
1. One umbilical vein carries
oxygenated blood from the placenta
to the foetus
2. Two umbilical arteries carry
deoxygenated blood from the foetus
to the placenta,
3. Remnants of the yolk sac and
allantois.
The Umbilical Cord

29. Insertion:
• The cord is inserted in the fetal
surface of the placenta near the
center "eccentric insertion"
(70%)
• Or at the center "central
insertion" (30%).
The Umbilical Cord

30. Abnormalities Of The
Umbilical Cord

31. (A) Abnormal cord insertion
1. Marginal insertion : in the placenta ( battledore insertion).
2.Velamentous insertion: in the membranes and vessels connect the
cord to the edge of the placenta.
(B) Abnormal cord length
1. Short cord which may lead to :
i.Intrapartum haemorrhage due to premature separation of the
placenta,
ii.Delayed descent of the foetus druing labour, iii-
Inversion of the uterus.
2. Long cord which may lead to
i-Cord presentation and cord prolapse, ii-Coiling
of the cord around the neck, iii-True knots of the
cord.
Velamentous
insertion

32. Chorion
Chorion
1 extraembryonic
mesoderm
2 cytotrophoblast
3 Syncytiotrophoblast
• Definition : Chorion is the name given
to the trophoblast after the formation
of the extraembryonic mesoderm
from its inner surface.
• The chorion is composed of :
• Syncito-trophoblast (outer layer).
• Cytotrophoblast (middle layer).
• Extra-embryonic mesoderm (inner
layer).

33. CHORION FRONDOSUM AND DECIDUA BASALIS
• In the early weeks of development, villi cover
the entire surface of the chorion . As pregnancy
advances, villi on the embryonic pole continue
to grow and expand, giving rise to the chorion
frondosum (bushy chorion). Villi on the
abembryonic pole degenerate and by the third
month this side of the chorion, now known as
the chorion laeve, is smooth.

34. C h o r i o n
• Chorionic villi cover the entire chorionic sac until the beginning of 8th week
• As this sac grows, the villi associated with decidua capsularis are compressed, reducing the
blood supply to them
• These villi soon degenerates producing an avascular bare area smooth chorion (chorion
laeve)
• As the villi disappear, those associated with the decidua basalis rapidly increase in number
• Branch profusely and enlarge
• This bushy part of the chorionic sac is villous chorion

35. CHORIONIC VELLI
• By the beginning of the third week, the trophoblast is characterized by
primary villi that consist of a cytotrophoblastic core covered by a syncytial
layer. During further development, mesodermal cells penetrate the core of
primary villi and grow toward the decidua. The newly formed structure is
known as a secondary villus .
• By the end of the third week, mesodermal cells in the core of the villus begin
to differentiate into blood cells and small blood vessels, forming the villous
capillary system . The villus is now known as a tertiary villus or definitive

36. P R I M A R Y v i l l o u s
•Growth of these
extensions are caused
by underlying
extraembryonic
somatic mesoderm
•The cellular
projections form
primary chorionic
villi

37. SECONDARY CHORIONIC VILLI
Early in 3rd
week,
extraembryonic
mesoderm
extends inside
the villi

38. Tertiary villus
During 3rd week, arterioles,
venules & capillaries develop
in the mesenchyme of villi &
join umbilical vessels
By the end of 3rd week,
embryonic blood begins to
flow slowly through
capillaries in chorionic villi

39. Dec i d u a
• The gravid endometrium is known as
decidua
• It is the functional layer of endometrium in
a pregnant woman
• This part of the endometrium separates
from the rest of the uterus after
parturition

40. Parts of decidua
• Decidua basalis: It is the part of decidua
between blastocyst and myometrium. It
forms the fetal part of placenta.
• Decidua capsularis: It covers the
blastocyst except embryonic pole and
separates it from uterine cavity.
• Decidua parietalis: It is the rest of
endometrium that lines the rest of
uterine cavity.

41. Fate of decidua
delivery.
Decidua basalis
Amniotic cavity
• Decidua basalis shares in the
formation of placenta.
• Decidua capsularis and
parietalis fuse together and
shedded with placenta after
Fused decidua paritalis ,
chorion laeve and amnion

42. P L A C E N T A
• This is a fetomaternal organ.
• It has two components:
• Fetal part – develops from the chorion
frondosum )
• Maternal part – derived from the decidua
basalis )

44. • During the 4th and 5th month, the decidua forms a numberof
decidual septa, which project into the intervillous space.
• As a result of this septum formation, the placenta is divided
into a number of compartments (cotyledons).

45. PLACENTAL MEMBRANE (placentalbarrier)
• This is a composite structure that separating the fetal blood from the
maternal blood.
• Early placental barrier : (It has four layers):
• Syncytiotrophoblast
• Cytotrophoblast
• Connective tissue of villus
• Endothelium of fetal capillaries
• Late placental barrier : After the 20th week, the cytotrophoblastic cells
disappear and the placental membrane consists only of
• 2 layer:
• Syncytiotrophoblast
• Endothelium of fetal capillaries

46. It separates fetal from maternal
blood.
It prevents mixing of them.
It is an incomplete barrier as it
only prevents large molecules to
pass ( heparin & bacteria)
But cannot prevents passage of
viruses(e.g. rubella), micro-
organisms(toxoplama, treponema
pallidum) drugs and hormones.

47. is discoid in shape.
 Diameter = 15-25 cm,
 2-3 cm thick,
 Weight = 0.5 kg.
 Umbilical cord is attached to its center.
Position : in the upper uterine
segment (99.5%), either in the posterior
surface (2/3) or the anterior surface
(1/3).
The full term placenta

48. 1 Fetal surface: which is smooth and
shinny because it is covered by an
amniotic membrane. The umbilical cord
is attached centrally to this surface.
2 Maternal surface: which is rough,
reddish, and has 15 – 20 elevated areas
called cotyledons with deep grooves in
between made by the decidual septa.
Surfaces

49. Function of placenta:-
1. Respiratory function
2. Excretory function
3. Nutritional function
4. Endocrine function:- placenta acts as endocrine
gland
5. Barrier function:- prevents transfer of maternal
infection.
6. Enzymatic action-
7. Immunological function:- ig G.

50. Abnormalities ofplacenta
1- Abnormal position: Placenta Previa
the placenta is attached to the lower uterine segment (due to low level of
implantation of the blastocyst). It causes severe antepartum haemorrhage.
There are three types:
Marginalis
Laterali
s
(parietal
is)
Centralis
the placenta does not reach the
internal os of the cervix.
the margin of the placenta overlies
the internal os of the cervix.
the center of the placenta
overlies the internal os
of the cervix .

51. 2- Abnormal adhesion:
1Placenta accreta: due to abnormal
adhesion between the chorionic villi and
the uterine wall.
2Placenta percreta: The chorionic villi
penetrate the myometrium all the way to
the perimetrium.
- the placenta fails to separate from the
uterus after birth and may cause severe
postpartum hemorrhage.