Foetal Development

Question 1

What is a cordocentesis?

Answer 1

A cordocentesis is a procedure used to take a sample of fluid from the base of the umbilical cord.

Question 2

List the events that occur in week 1 of gestation.

Answer 2

Week 1:

1 - Fertilisation.

2 - Blastocyst formation.

3 - Implantation.

Question 3

What occurs in week 2 of gestation?

Answer 3

In week 2 of gestation, the bilaminar germ disc forms, comprising the epiblast and hypoblast.

Question 4

What occurs in week 3 of gestation?

Answer 4

In week 3 of gestation, gastrulation occurs to form the trilaminar germ disc:

• Endoderm – formed by epiblast cells that migrate through the primitive streak and displace the hypoblast cells.
• Mesoderm – formed by epiblast cells that migrate through the primitive streak and lie between the epiblast layer and the newly created endoderm.
• Ectoderm – formed by the epiblast cells that remain in position.
• The hypoblast disappears.

Question 5

What occurs in week 4 of gestation?

Answer 5

In week 4 of gestation, neurulation occurs (the transformation of the neural plate into the neural tube explain later in more detail).

Question 6

List 2 tissues / organs that originate from the ectoderm.

Answer 6

The ectoderm gives rise to:

1 - The epidermis.

2 - Neural tissue.

Question 7

List 5 tissues / organs that originate from the mesoderm.

Answer 7

The mesoderm gives rise to:

1 - Cardiac muscle.

2 - Skeletal muscle.

3 - Smooth muscle.

4 - Kidney tubules.

5 - Red blood cells.

Question 8

List 6 tissues / organs that originate from the endoderm.

Answer 8

The endoderm gives rise to:

1 - Lungs.

2 - Thyroid gland.

3 - Pancreas.

4 - Liver.

5 - Colon.

6 - GIT.

Question 9

How does the trilaminar disc fold to form a cylindrical embryo?

Answer 9

• Cephalocaudal folding occurs in the longitudinal direction.
• Lateral folding occurs in the lateral / transverse direction.

Question 10

List the phases of foetal development (different to the phases of foetal growth as seen in the last lecture).

Answer 10

1 - Embryonic period (weeks 3-8):

• Organogenesis.
• Establishment of the main organ systems

2 - Foetogenesis (weeks 9-38):

• Maturation and growth of tissues.

Question 11

List the types of birth defect.

Answer 11

1 - Structural birth defect.

2 - Functional birth defect.

3 - Metabolic birth defect.

Question 12

What is the difference between a malformation, disruption and deformation?

Answer 12

• Malformation refers to abnormal formation of a structure.
• Disruption refers to alterations to an already-formed structure due to an intrinsic destructive process.
• Deformation refers to alterations to an already-formed structure due to an extrinsic mechanical factor.

Question 13

What is the difference between a syndrome, association and sequence?

Answer 13

• A syndrome is a group of abnormalities which tend to occur together with a specific known cause.
• An association is a group of abnormalities which tend to occur together without a specific known cause.
• A sequence is a cascade of abnormalities.

Question 14

Which chromosome is affected in Down’s syndrome?

Answer 14

Down’s syndrome is caused by trisomy of chromosome 21.

Question 15

List 6 features of Down’s syndrome.

Answer 15

1 - Congenital heart defects.

2 - Duodenal atresia (closure of the duodenum).

3 - Learning difficulties.

4 - Early onset Alzheimer’s.

5 - Single palmar crease.

6 - Wide sandal gap.

Question 16

How does the trisomy occur in Down’s syndrome?

Answer 16

• 94% of trisomy 21 is caused by nondisjunction.

- 6% of trisomy 21 is causes by robertsonian translocation.

Question 17

Define teratogen.

Answer 17

A teratogen is an agent that can predispose to a birth defect.

Question 18

List 6 teratogenic drugs.

Answer 18

1 - Alcohol.

2 - Cocaine.

3 - Thalidomide.

4 - Anticonvulsants.

5 - Antipsychotics.

6 - Warfarin.

Question 19

List 2 teratogenic infectious agents.

Answer 19

1 - Rubella.

2 - CMV.

Question 20

List 2 teratogenic maternal factors.

Answer 20

1 - SLE.

2 - Poorly controlled pre-existing DM.

Question 21

List 3 teratogenic mechanical factors.

Answer 21

1 - Malformed uterus.

2 - Oligohydramnios.

3 - Amniotic band syndrome.

Question 22

What is amniotic band syndrome?

Answer 22

Amniotic band syndrome is a birth defect in which bands of tissue in the amniotic sac tangle the foetus.

Question 23

How do teratogens affect foetal development at different points in development?

Answer 23

• Prior to organogenesis, teratogens either cause miscarriage or have no effect.
• Organogenesis is the period of greatest sensitivity to teratogens, and is where most birth defects arise.
• During foetogenesis, the foetus is only significantly sensitive to functional birth defects.

Question 24

How does spina bifida arise?

Answer 24

Spina bifida arises from failure of closure of the caudal end of the neural tube.

*Anencephaly is caused by failure of closure of the rostral end of the neural tube.

Question 25

List the types of spina bifida. What is the difference between each type?

Answer 25

1 - Spina bifida occulta (a bony defect in which no tissue extrudes from the spinal cord). 2 - Spina bifida meningocele (only the meninges extrude from the spinal cord). 3 - Spina bifida myelomeningocele (both the meninges and the neural tissue extrude from the spinal cord).

Question 26

What is the lemon sign?

Answer 26

- The lemon sign refers to excessive concavity of the frontal bones seen on an ultrasound of the foetal skull. - It is a feature of spina bifida.

Question 27

What is the banana sign?

Answer 27

- The banana sign refers to excessive curvature of the cerebellum seen on an ultrasound of the foetal skull. - It is a feature of spina bifida.

Question 28

How is spina bifida prevented?

Answer 28

Folic acid prevents spina bifida.

Question 29

How does cleft lip occur during development?

Answer 29

- During development, the face has 5 prominences: 1 - 2x maxillary prominences. 2 - 2x mandibular prominences. 3 - 1x frontonasal prominence. - The frontonasal prominence develops invaginations, which become the nasal pits (precursors to the nostrils). - Lateral and medial nasal prominences develop around the nasal pits. - The maxillary prominences grow medially to merge with the medial nasal prominences. - Fissures form where the maxillary prominences grow into the medial nasal prominences. These fissures normally close to form the upper lip. - Failure of these fissures to close result in cleft lip.

Question 30

What is an omphalocele?

Answer 30

- An omphalocele is an abdominal wall defect in which the abdominal viscera herniate into the umbilicus. - This results in a thin, transparent sac of amnion containing the abdominal contents protruding from the abdomen.

Question 31

What is gastroschisis?

Answer 31

- Gastroschisis is an evisceration of the foetal intestine through the umbilicus. - The intestine is not contained within a sac as in an omphalocele.

Question 32

What is a nuchal translucency?

Answer 32

- A nuchal translucency is a scan to measure the size of a fluid-filled subcutaneous space at the back of the head of the foetus. - A larger space indicates a higher risk of Down's syndrome. * This is usually done in combination with blood markers.

Question 33

How does non-invasive prenatal testing work?

Answer 33

- A sample of maternal blood is taken. - Foetal DNA is extracted from the maternal blood. - The DNA is used to test for genetic abnormalities.

Question 34

List 7 methods of prevention of pre-conception birth defects.

Answer 34

1 - Vaccination (e.g. Rubella). 2 - Avoidance of teratogenic substances. 3 - Folic acid supplements. 4 - Nutrition (e.g. iodine). 5 - Optimise disease control (e.g. diabetes). 6 - Maternal age. 7 - Prenatal testing.

Question 35

Which factors of the immune system of the mother must be balanced during pregnancy?

Answer 35

The mother's immune tolerance to the foetus must be balanced with the protective ability to fight infections.

Question 36

List 6 mechanisms that contribute to the modulation of the maternal T cell response to the foetus.

Answer 36

1 - Reduced MHC expression of the trophoblast. 2 - FAS-ligand dependent deletion of local T cells. 3 - Induction of Th1 to Th2 shift by altered T cell cytokine production. 4 - Recruitment of Tregs. 5 - Hormonal immunomodulation. 6 - Deletion of foetal-specific T cells.