Fetal development

Question 1

Fetal developement

• Features

Answer 1

Rate of fetal growth increases after 10 weeks due to massive increase in cells (actual gain weight is small)
and diminishes again towards term (rapid increase in weight until full-term fetus ~ 3.5 kg).

§ Fetal birth-weight is determined by gestational age, race, maternal height and weight and parity. From all the
factors and history, a nomogram for growth can be calculated.

§ Protein accumulation occurs throughout the pregnancy.
§ Fatty acids are stored as brown fat around neck, behind scapula and around kidneys.

§ White fat forms the subcutaneous fat covering the body of full-term fetus.

Question 2

Time points of fetal developement

Answer 2

W 12,16,24

Question 3

Fetus at week 12 characteristics

Answer 3

Translucent skin, virtually no subcutaneous fat where vessels can be seen clearly.
- Upper limbs have reached their final relative length.
- External genitals are distinguished externally but remain undifferentiated.

Question 4

Fetus at week 16 characteristics

Answer 4

Crown-rump length ~ 122 mm and lower limbs have achieved their final relative length.
- External genitals can now be differentiated.

Question 5

Fetus at week 24 characteristics

Answer 5

Crown-rump length ~ 210 mm.
- Eyelids are separated.
- Skin is opaque but wrinkled because of the lack of subcutaneous fat.
- Fine hair covering the body.

Question 6

Heart development

Answer 6

Heart develops as single tube and heartbeat present at 4–5 weeks (65 bpm).

§ Definitive circulation develops at week 11.

§ In mature fetal circulation, 40% of venous return entering RA flows directly to LA through foramen ovale.
Blood pumped from RA to RV is expelled to pulmonary artery where is passes either through aorta via
ductus arteriosus or into the pulmonary vessels.

Question 7

Lungs dev

Answer 7

§ Fetal respiratory movement detected at 12 weeks, and regular respiratory pattern by mid-trimester.

§ 40–60 movements/min at 34 weeks with intervening periods of apnea. Movements are shallow.

§ Amniotic fluid enters the bronchial tree but doesn’t reach alveoli due to high pressure maintained from the
secretion of alveolar fluid. Exception of this situation may lead to hypoxia.

§ Fetal breathing is stimulated by hypercapnia and raised maternal glucose level where smoking and hypoxia
reduces respiratory
movements.

§ Principal surfactants sphingomyelin and lecithin; production of lecithin reaches functional levels by 32 weeks
but surfactant production may be delayed by maternal diabetes (corticosteroids required).

§ By week 16-20, mucosal glands appear and most digestive enzymes present by 26 weeks

Amylase activity
doesn’t appear until neonatal period.

Question 8

Alimentary canal dev

Answer 8

The fetus swallows amniotic fluid and gut peristaltic movement is established by mid-pregnancy.

§ The digestion of cells and proteins in amniotic fluid results in meconium formation where normally it appears
in the gut and increases in amniotic fluid with increasing maturity and under fetal stress.

Question 9

Kidneys dev

Answer 9

Fetal kidney completely formed by 36 weeks but most excretory functions performed by the placenta.
§ Glomerular filtration increases towards term as number of glomeruli increases and fetal bp rises.

Question 10

Sound and visual perceptions dev

Answer 10

§ Perception of sound begins between 16 and 24 weeks and visual perception to light through abdomen
develop.
§ Certainly, the eye movements are observed.