Fetal Growth & Devlopment

Question 1

What are the three stages after fertilisation until birth and how long is each?

Answer 1

Pre- embryonic week1-3

Embryonic 3-9

Fetal 9-38

But pregnancy weeks calculated from date LMP so add +2 weeks to conception - term is 40 pregnancy weeks

Question 2

Describe the growth that occurs at each stage

Answer 2

Embryonic period - intense activity morphogenesis & differentiation, organogenetic period, absolute growth is v small (bar placenta)

Fetal period - growth & weight gain accelerate
Early: protein deposition
Late: adipose deposition

Crown-rump growth increases rapidly in all periods (PE, E but just early fetal)

9 weeks - 5cm, head approx half body CRL
20 weeks - 19cm
38 weeks - 36cm

Length of foetus Cm roughly time in weeks

Question 3

What are some ante-natal assessments of fetal wellbeing?

Answer 3

Mother can judge fetal movements in 2nd trimester usually weeks 15-16

Regular measurements of uterine expansion (symphysis- fundal height)
(Pubic symphysis to top most portion of the uterus)

Ultrasound scan

Question 4

What is obstetric ultrasound scan used for and when is it done?

Answer 4

Safe, can be used early in pregnancy to calculate age, rule out ectopic, number of fetuses, assess fetal growth and abnormalities

Routinely carried out at 20 weeks (big enough to make good assessment and still time abortion)

Question 5

How can we estimate fetal age?

Answer 5

LMP - prone to inaccuracy

Developmental criteria:

Crown- rump length, measured 7-13 weeks gives estimate EDD, scan in T1 also to check location, number, viability

Biparietal diameter, distance between parietal bones of fetal skull, used in combo with abdominal circumference and femur length to date pregnancies in T2 & T3, scan also used anomaly detection

Question 6

What’s the classification of birth weights?

Answer 6

3500g/ 3.5kg - average

<2500g suggests growth restriction

> 4500g macrosmic (maternal diabetes)

Many factors influence birth weight not all pathological e.g. small mothers = small babies ‘constitutionally small’

Question 7

Reasons why babies may have low birth weight

Answer 7

Premature

Constitutionally small

Suffered growth restriction (high neonatal morbidity and mortality)

Question 8

Explain how the lungs develop

Answer 8

Relatively late

Embryonic period only creates: bronchopulmonary tree (respiratory diverticulum off primitive gut tube -> tracheoesophageal septum forms -> 2 main bronchi

functional specialisations fetal period:

• 9-16: ‘pseudoglandular stage’ bronchioles & a duct system begins to form within the bronchopulmonary segments
• 16-26: ‘canalicular stage’ respiratory bronchioles bud off terminal bronchioles
• 26: ‘terminal sac stage’ alveolar bud from respiratory bronchioles, type 1 & 2 (make surfactant) pneumocytes

Question 9

How do the respiratory muscles become conditioned in terms one and two?

Answer 9

Gas exchanged conducted at placenta but lungs must be prepared to assume full burden at birth so amniotic fluid fills them to cause breathing movements - crucial for normal lung development

Question 10

What determines the threshold for viability?

Answer 10

Viability is only possible once lungs have entered the terminal sac stage and can live independently from their mother

This is why abortion is allowed up to 24weeks in UK

Question 11

What occurs if babies have to be born pre-term? What can be done to prevent this?

Answer 11

Respiratory distress syndrome - insufficient surfactant and lungs collapse

If known that pre-term delivery will occur - mother glucocorticoid treatment increases surfactant production in foetus

Question 12

When is the definitive fetal heart rate achieved?

Answer 12

around 15 weeks

Fetal bradycardia associated with fetal demise

Question 13

When does the fetal kidneys function begin? What does it produce? What if it doesn’t function properly?

Answer 13

Week 10

Fetal urine contributes to amniotic fluid volume

If kidney function not working -> oligohydramnios (small volumes of amniotic fluid)

Question 14

What occurs if you have too much or too little amniotic fluid volume?

Answer 14

Oligohydramnios- too little -> placenta, insufficiency, fetal renal impairment

Polyhydramnios - too much could be fine but -> fetal abnormality e.g. inability to swallow (misplacement tracheoesophageal septum)

Normal volume: 10ml 8weeks, 1litre 38weeks - falls away post EDD

Question 15

Describe the development of the nervous system

Answer 15

First to start Depop net and last to finish

Corticospinal tracts required for coordinated voluntary movements begin to form 4th month

Myelination of brain only begins 9th month

Corticospinal tract myelination incomplete at birth (increasing infant mobility in 1st yr)

Question 16

Describe motor changes in baby

Answer 16

No movement until 8th week -> large repertoire practicing for post-natal life e.g. suckling (sucking thumb), breathing (amniotic fluid), leg/arm/ head movements, hiccup, yawn

‘Quickening’ maternal awareness fetal movements from 17weeks (15-18 first pregnancy)