Placenta and Fetal Membranes

Question 1

What is oligohydramnios?

Answer 1

This is a condition in which a low volume of amniotic fluid is present for a given gestational age.

Question 2

What are some causes of oligohydramnios?

Answer 2

1. preterm rupture of amniochorionic membrane (most common cause)
2. renal agenesis (failure of kidneys to form), hence absence of fetal urine contribution to the amniotic fluid
3. obstruction of urinary tract of foetus
4. compression of the umbilical cord

Question 3

What are some complications of oligohydramnios?

Answer 3

1. pulmonary hypoplasia (incomplete development of lung tissue)
2. facial and limb defects e.g. congenital talipes equinovarus
3. Potter’s sequence (an array of complications including all of the above, and resulting from severe oligohydramnios)

Question 4

What is polyhydramnios?

Answer 4

This refers to an excess of amniotic fluid for a given gestational age.

Question 5

What is the main technique used to detect oligohydramnios and polyhydramnios?

Answer 5

ultrasonography

Further notes:
Ultrasonography is a type of medical imaging that uses high-frequency sound (ultrasound) waves to produce images of internal organs and other tissues. During an ultrasound, a device called a transducer converts electrical current into sound waves, which are sent into the body’s tissues.

Question 6

What are the functions of amniotic fluid in the normal development of the foetus?

Answer 6

1. it permits symmetric external growth of the fetus/embryo
2. it acts as a barrier to infection
3. it permits normal fetal lung development
4. it prevent adherence of the amnion to the embryo/fetus
5. cushions the embryo/fetus against injuries by distributing impacts the mother receives
6. helps control the embryo/fetus’s body temperature by maintaining a relatively constant temperature
7. it enables the fetus to move freely, thereby aiding in muscular development
8. assists in maintaining homeostasis of fluid and electrolytes

Question 7

What is amniotic band syndrome?

Answer 7

This is a condition caused by strands of the amniotic sac that separate and entangle digits, limbs or other parts of the fetus.

Question 8

A fetus with esophageal atresia will often develop oligohydramnios, true or false?

Answer 8

False. A fetus with esophageal atresia usually develops polyhydramnios. Esophageal atresia is a congenital anomaly whereby the esophagus connects with the trachea. The fetus is hence unable to absorb amniotic fluid through the gut.

Question 9

What is the decidua? What are the three parts of the decidua?

Answer 9

(a) The decidua is the endometrium of the uterus in a pregnant woman.
(b) Parts of the decidua:
1. decidua basalis: part of the decidua deep to the conceptus, which forms the maternal part of the placenta
2. decidua capsularis: this is the superficial part of the decidua overlying the conceptus
3. decidua parietalis: part of the decidua that is not beneath the placenta
4. [Diagram]

Question 10

What are the two parts of the placenta and what are they formed by?

Answer 10

1. Fetal part - formed by villous chorion
2. Maternal part - formed by decidua basalis
3. [Diagram]

Question 11

The fetal part of the placenta is attached to the maternal part by the _________.

Answer 11

cytotrophoblastic shell

Question 12

What is the fate of the amniotic sac?

Answer 12

1. Tears around the time of delivery during “rupture of membranes”.
2. The membrane is expelled “after birth” together with the placenta.

Question 13

What are the disadvantages of amniocentesis over chorionic villous sampling?

Answer 13

• risk of amniotic fluid embolism (when fluid goes into maternal circulation)
• may induce oligohydramnios
• may have misinterpretations especially if there are twins or vanishing twins
• cannot be done early during pregnancy, but can be done after 10 weeks

Question 14

What are some causes of polyhydramnios?

Answer 14

(a) Causes as a result of reduced clearance:
Reduced fetal swallowing because of
● obstructive anomalies of the GIT
- esophageal atresia
- duodenal atresia
● defective swallowing reflex
- CNS anomalies
- craniofacial anomalies

(b) Causes as a result of increased production:
Multiple pregnancy

Other causes:
maternal diabetes, maternal CCF (congestive cardiac failure), foetal cardiac anomalies, aneuploidy e.g. Trisomy 21

Question 15

State the complications of polyhydramnios.

Answer 15

1. Pre-term rupture of membranes.
2. Risk of umbilical cord falling down when rupture has occurred is high (cord prolapse).
3. Risk of the cord going around the neck is high. This is termed nuchal cord and may lead to cerebral palsy among other complications.
4. True knot.
5. Risk of malpresentation is high.

Question 16

State 5 results of longitudinal folding. (Brief note: Remember that this kind of folding happens in the cranio-caudal axis.)

Answer 16

1. Primary curvature formation
2. Descent of heart
3. Connecting stalk formation
4. Amniotic cavity expansion
5. Oesophagus elongation

Question 17

State the timelines of splitting of the conceptus that will result in the following types of monozygotic twins:
a) dichorionic-diamniotic
b) monochorionic-diamniotic
c) monochorionic-monoamniotic
d) conjoined twins

Answer 17

a) 0 - 72 h (zygote/morula)
b) 4 - 8 days (blastocyst)
c) 9 - 12 days (implanting blastocyst)
d) > 12 days (embryonic disk - primitive streak stage)

Question 18

What is twin-twin transfusion syndrome? How does it present? How is it treated?

Answer 18

1. Placental anastomoses are formed such there is shunting of arterial blood from one twin through arterio-venous anastomoses into the venous circulation of the other twin.
2. The donor twin is small, pale and anemic, whereas the recipient twin is large and has polycythemia, an increase above the normal in the number of red blood cells.
3. Fetoscopic laser coagulation of placental vascular anastomoses

Question 19

What are the sources of the amniotic fluid?

Answer 19

maternal plasma, fetal urine, lung secretions of fetus, gastrointestinal secretions and excretions of fetus

Question 20

What are functions of the allantois?

Answer 20

1. blood cell formation occurs in its wall during the third to fifth weeks
2. its blood vessels persist as the umbilical vein and arteries
3. It forms the urachus during fetal development and after birth it forms the median umbilical ligament.

Question 21

Briefly comment on the following placental anomalies.
1. Placenta previa
2. Battledore placenta

Answer 21

1. Placenta previa: implantation of the placenta over the opening of the cervix
2. Battledore placenta: condition in which the umbilical cord is inserted near the placental margin rather than at the centre

Question 22

Briefly comment on the following placental anomalies:
1. Bilobed placenta
2. Circumvallate placenta

Answer 22

1. Bilobed placenta: placenta separated into two near equal-sized lobes
2. Circumvallate placenta: due to a small chorionic plate, the amnion and chorion fetal membranes ‘double-back’ around the edge of the placenta [Picture] [“circumvallate” describes something that is surrounded by or as if by a rampart]

Question 23

Briefly comment on the following placental anomalies:
1. Placenta velamentosa
2. Placenta succenturiata
3. Placenta accreta, increta and percreta

Answer 23

1. Placenta velamentosa: insertion of the umbilical cord into the amniotic membrane rather than placenta
2. Placenta succenturiata: presence of one or more accessory lobes of the placenta [The term “succenturiate” is used in anatomy and it means accessory or serving as a substitute. It is often used to describe an organ that is supplementary or additional to a main organ.]
3. Placenta accreta: placenta grows too deeply into the uterine wall, placenta increta: placenta attaches even more deeply than in accreta, placenta percreta: more severe, placenta grows through uterus, may even extend to urinary bladder [Diagram 1] [Diagram 2]

Question 24

State the consequence of true knot.

Answer 24

Cutting of oxygen supply to head of foetus/perinatal asphyxiation.