(9.1+2) Foetal Growth Flashcards
State the periods of Pre-embryonic, Embryonic and Fetal.
- Pre-embryonic: fertilisation - week 3
- Embryonic: week 3- week 8
- Fetal: week 8 - week 38
State the periods of the 3 trimesters.
- 1st: week 1 - 12
- 2nd: week 13 - 28
- 3rd: week 29 - 40
Describe the fetal proportion during pregnancy.
- At week 9, head is almost 50% of Crown Rump Length
- Then body length & lower limbs grow faster
- At birth, head is about 1/4 of Crown Rump Length
Describe the important stages of development of the Respiratory system.
- Very late, not needed until birth
- Embryonic development: Bronchopulmonary Tree from Primitive Gut Tube
- Pseudoglandular Stage: Bronchioles develop
- Terminal Sac Stage: Respiratory Bronchioles + Pneumocytes differentiate (e.g. Type 2 produce few Surfactant)
- Alveolar Period: complete Alveoli & Surfactant (continues till 8yrs old)
At which stage is surfactant starting to be produced? When does it start to increase dramatically? When is it fully developed?
- Starting at week 20
- Increases dramatically at week 30
- Not complete till 8 years old
What structure is the embryonic kidney? When does it start to function? How does the level of urine change in pregnancy?
- Metanephros starts week 10
- Week 25: 100ml/day
- Term: 500ml/day
Amniotic fluid is turned over rapidly, how is it achieved?
- Early pregnancy: produced from maternal fluid & fetal extracellular fluid
- Late pregnancy: by foetus
- Swallowed by foetus to balance volume
What are the names given when the amniotic fluid is reduced and in excess? Suggest some causes for each.
Oligohydraminos
- Pre-eclampsia
- Placenta insuficcient
- Excess skin absorption
- Failure of embryonic kidneys
- Tetralogy of fallot
- Premature rapture of membranes
Polyhydraminos
- Foetal oesophageal/duodenal atresia
- Diabetes mellitus
- Foetal excretory problem
What is Meconium?
- Foetus swallows the amniotic fluid in, the debris accumulates in foetal gut, together with foetal debris called Meconium
- Normally newborn’s first poo, but if found in amniotic fluid is a sign of foetal distress
What factors determine the viability of a foetus if it was to be born pre-rem?
- Development of Terminal Sacs with some Surfactant production
- Brain development to ensure body function e.g. breathing
Respiratory Distress Syndrome is commonly seen in pre-term neonate, what is it and how is it treated if pre-term is unavoidable?
- Type 2 Pneumocytes unable to produce Surfactant -> Alveoli collapse
- Pre-partum, mother is given Corticosteroid to stimulate Type 2 Pneumocytes hence Surfactant
- Post-partum, artificial surfactant
Suggest ways to access fetal size. When are they each performed?
Ultrasound
- Crown-Rump Length used in T1
- Biparietal diameter of head used in T2&3
Symphysis-fundal height used from week 12 onwards
Suggest ways of fetal biophysical assessment.
- Fetal movement: >3 gross movements in 30mins
- Fetal tone: >1 flexion-extension-flexion in 30 mins
- Fetal heart rate
- Amniotic volume
- Non-stress test: changes of fetal heart rate according to fetal movement
When do foetus start to move? When does the mother begin to feel them?
- Begin around week 8
- But felt around week 17, known as Quickening
Suggest the possible complications due to poor nutrition to the foetus in early and late pregnancy.
- Early -> Neural tube defect e.g. DiGeorge syndrome
- Late -> Asymmetrical growth restriction -> Oligohydraminos
Define the ranges of neonate body weight.
- Below 2500g = growth restriction
- 3500g = average
- Above 4500g = Macrosomia
Describe the fetal circulation before birth.
- Oxygenated blood: mom - 1 Umbilical Vein -> foetus
- Deoxygenated blood: foetus - 2 Umbilical Arteries -> mom
- Right Atrium - Foramen Ovale -> Left Atrium
- Pulmonary Artery - Ductus Arteriosus -> Aorta
- Ductus Venosus - bypass -> Liver
What happens to the breakdown product of fetal Haemoglobin?
- Becomes Unconjugated Bilirubin
- Cross placenta to mother
- Conjugated by mother
- Excreted as Bile
How does the fetal circulation change after birth?
- Within minutes, first breath -> removes Hypoxic Pulmonary Vasoconstriction -> pressure in LA larger than RA -> closes Foramen Ovale
- Within hours, increased O2 saturation + reduced Prostaglandin from removal of Placenta -> Vasoconstriction of Ductus Arteriosus & Umbilical Arteries
- Within days, stasis of blood -> fibrosis of Ductus Venosus & Umbilical Vein
What is the normal fetal O2 saturation? How do their haemoglobin achieve the same level of O2 delivery?
- Fetal pO2 = 4pKa
- No beta-chain -> higher affinity
- Double Bohr Effect: both mother and foetus circulations have high [H+] and pCO2
Foetus cannot tolerate high pCO2, how is it prevented?
- Maternal hyperventilation -> reduce pCO2
- Stimulated by Progesterone
Describe how a Symphysis-Fundal Height is measured. What are the normal findings at week 20 and 36?
- Tape measures from Pubic symphysis to Uterine Fundus
- Week 20: 20cm from symphysis e.g. Umbilicus
- Week 36: 36cm from symphysis e.g. Xiphisternum Joint
In what situations might measuring Symphysis-Fundal Height be problematic?
- Unusual lie of foetus
- Irregularity of amniotic fluid
- Multiple foetus’
What systems does the foetal non-stress test measure?
- CVS
- Nervous system
- MSK
