S7) Foetal Growth and Development

Question 1

What is the foetal period and what happens during this?

Answer 1

• The foetal period is the period involving preparation for the transition to independent life after birth
• Growth and physiological maturation of the structures created during the embryonic period occurs

Question 2

What characterises the embryonic period?

Answer 2

Embryonic period is characterised by intense activity (organogenetic period) but absolute growth is very small

Question 3

What is crown-rump length?

Answer 3

Crown-rump length (CRL) is the measurement of the length of human embryos and fetuses from the top of the head (crown) to the bottom of the buttocks (rump)

Question 4

Describe the differential growth observed in the crown-rump length

Answer 4

CRL increases rapidly in the pre-embryonic, embryonic & early fetal periods

Question 5

Describe how weight gain varies in the different foetal periods

Answer 5

• Embryo – intense morphogenesis & differentiation; little weight gain; placental growth most significant
• Early foetus – protein deposition
• Late foetus – adipose deposition

Question 6

Explain how body proportions change during the foetal period

Answer 6

• 9 weeks, the head is approx half crown-rump length
• Thereafter, body length & lower limb growth accelerates

Question 7

Identify and describe 3 different ways of assessing foetal well-being

Answer 7

• Mother – foetal movements
• Regular measurements of uterine expansion – symphysis-fundal height
• Ultrasound scan

Question 8

Obstetric ultrasound scan (USS) is routinely carried out at ~20 weeks.

Identify 5 advantages of this

Answer 8

• Safe
• Can be used early in pregnancy to calculate age
• Rules out ectopic pregnancy
• Indicates number of foetuses
• Assess foetal growth and anomalies

Question 9

Identify and describe 2 different ways of estimating foetal age

Answer 9

• Last menstrual period (LMP) – prone to inaccuracy
• Developmental criteria – allows accurate estimation of fetal age

Question 10

Why and when do we measure crown-rump length?

Answer 10

Measured between 7 & 13 weeks to date the pregnancy and estimate EDD

Question 11

What is biparietal diameter and when is it used?

Answer 11

• Biparietal diameter is the distance between the parietal bones of the fetal skull
• Used in combination with other measurements to date pregnancies in T2 & T3

Question 12

When is abdominal circumference and femur length used?

Answer 12

• AC & FL used in combination with BPD for dating and growth monitoring
• Useful for anomaly detection

Question 13

How do we classify birth weights?

Answer 13

• Average: 3500 g
• Growth restriction: < 2500 g
• Macrosomia: > 4500 g (maternal diabetes)

Question 14

Provide 3 possible reasons for low-birth weight

Answer 14

• They are premature
• They are constitutionally small
• They have suffered growth restriction (associated with neonatal morbidity & mortality)

Question 15

The lungs develop relatively late.

Why is this?

Answer 15

• Embryonic development creates only the bronchopulmonary tree
• Functional specialisation occurs in the foetal period

Question 16

Identify the different stages in the development of the respiratory system

Answer 16

• Weeks 8 – 16: pseudoglandular stage
• Weeks 16 – 26: canalicular stage
• Weeks 26 – term: terminal sac stage

Question 17

Describe the pseudoglandular stage in lung development

Answer 17

• Duct system begins to form within the bronchopulmonary segments created during the embryonic period
• Forms bronchioles

Question 18

Describe the canulicular stage in lung development

Answer 18

Formation of respiratory bronchioles through budding from bronchioles formed during the pseudoglandular stage

Question 19

Describe the terminal sac stage in lung development

Answer 19

• Terminal sacs begin to bud from the respiratory bronchioles
• Type I & Type II pneumocytes differentiate
• Surfactant is produced

Question 20

Gas exchange is conducted at placenta, but lungs must be prepared to assume full burden at birth.

How does this happen in T2 and T3?

Answer 20

• “Breathing” movements condition of the respiratory musculature
• Fluid filled spaces crucial for normal lung development

Question 21

Discuss the threshold for viability in terms of pre-term survival

Answer 21

Viability is only a possibility once the lungs have entered the terminal sac stage of development (> 24 weeks)

Question 22

Respiratory distress syndrome often affects infants born pre-maturely and involves insufficient surfactant production.

How can this be treated?

Answer 22

Glucocorticoid treatment (of the mother) increases surfactant production in foetus if preterm delivery is inevitable/unavoidable

Question 23

When is the definitive foetal heart rate determined?

Answer 23

• The definitive fetal HR is achieved at around 15 weeks
• Foetal bradycardia is associated with fetal demise

Question 24

Describe the development of the urinary system in the foetus and the importance of such

Answer 24

• Foetal kidney function begins in week 10
• Foetal urine is a major contributor to amniotic fluid volume

Question 25

Describe the variations in amniotic fluid volume

Answer 25

- **Oligohydramnios**: too little amniotic fluid due to placental insufficiency or fetal renal impairment - **Polyhydramnios**: too much amniotic fluid due to foetal abnormality *e.g. inability to swallow*

Question 26

The nervous system is first to begin development and last to finish. Briefly outline its development

Answer 26

- **Corticospinal tracts** required for coordinated voluntary movements to begin to form in the 4th month - **Myelination of brain** only begins in 9th month

Question 27

Outline the development of sensory and motor systems

Answer 27

- No movement until the **8th week** - Thereafter a large repertoire of movements develop to “practise” for post-natal life *e.g. suckling, breathing*

Question 28

What is "quickening" and what is its the benefit?

Answer 28

- **Quickening** is the maternal awareness of fetal movements from 17 weeks onwards - It is a low cost, simple method of ante-partum fetal surveillance and reveals those foetuses requiring follow-up

Question 29

In terms of chronology, compare and contrast the development of the brain and lungs

Answer 29

Question 30

Identify 3 benefits of transvaginal ultrasound

Answer 30

- Check that conceptus implanted in correct place - Rule out ectopic pregnancy - Check for multiple foetuses

Question 31

Why are dietary supplements of folic acid recommended during pregnancy?

Answer 31

Folic acid prevents neural tube defects

Question 32

When can you hear a foetal heartbeat with a: - Doppler stethoscope - Plain stethoscope

Answer 32

- **Doppler stethoscope:** 10-12 weeks - **Plain stethoscope:** after 20 weeks

Question 33

What is the average foetal heart rate at term?

Answer 33

110 - 160 bpm at term (37 weeks)

Question 34

Which cells secrete surfactant?

Answer 34

Type II pneumocytes

Question 35

At what gestational age does surfactant production begin and how is this significant in prematurity?

Answer 35

- Surfactant begins production at **24-28 weeks** - Majority of surfactant is produced by **35 weeks,** hence is insufficient in premature babies

Question 36

What is symphysis-fundal height ?

Answer 36

**Symphysis-fundal height** is the distance from the pubic symphysis and the fundus of the uterus used to assess foetal growth and development during pregnancy

Question 37

Identify 3 sources of error for the symphysis-fundal assessment

Answer 37

- Human error (poor technique) - More/less than normal amniotic fluid volume - Later in pregnancy (foetal engagement, head moves, smaller fundus)

Question 38

Which factors must be considered in deciding whether to allow a compromised foetus to remain in utero?

Answer 38

- Mother's health - Foetal viability - Stage of pregnancy

Question 39

How is amniotic fluid produced prior to week 8?

Answer 39

Amniotic fluid is produced by **foetal cells in the amnion**

Question 40

Identify 5 conditions which would lead to decreased amniotic fluid volume

Answer 40

- Foetal kidney malfunction - Maternal hypertensive disorders - Premature rupture of membranes - Foetal bladder outlet obstruction - Premature leakage of amniotic fluid

Question 41

The foetus swallows and digests amniotic fluid. Identify a foetal GI tract defect that might lead to polyhydramnios

Answer 41

Defect in the **tracheal oesophageal septum** leads to blind-ended oesophagus (atresia) or fistula

Question 42

Identify 5 instances when a foetus would be classified as at-risk

Answer 42

- Growth restriction - Macrosomia - Poorly positioned - Multiple foetuses - Pre-eclamptic mother