Session 9 - Foetus and Foetal Growth Flashcards Preview

Semester 4 - Reproductive System > Session 9 - Foetus and Foetal Growth > Flashcards

Flashcards in Session 9 - Foetus and Foetal Growth Deck (67)

Define the pre-embryonic period

Fetilisation -> 3 weeks


Define the embryonic period

3 -> 8 weeks


Define the foetal period

8-38 weeks


What is the main method of measuring foetal size?

Crown Rump Length


What growth happens in the embryo?

 Intense morphogenesis and differentiation
 Little weight gain
 Placental growth most significant


What growth occurs in early foetus?

Protein deposition


What growth occurs in late foetus

Adipose deposition


What parts of respiratory system develop in the embryonic phase?

Bronchopulmonary tree, with airways but no gas exchanging parts


What significance does the late development of respiratory system have?

o Major implications for pre-term survival
 Threshold of Viability
 Viability is only a possibility after 24 weeks


What are the four stages of resp system development

Pseudoglandular stage
Terminal sac stage
Alveolar period


What is pseudoglandular stage?

o Weeks 8 – 16
o Duct systems begin to form within the bronchopulmonary segments created during the embryonic period
 Bronchioles


What is canalicular stage?

o Weeks 16 – 26
o Formation of respiratory bronchioles
 Budding from bronchioles formed during the pseudoglandular stage
o May be viable at the end
o More vascular
o Some terminal sacs


What is terminal sac stage?

o Week 26 – Term
o Terminal sacs begin to bud from the respiratory bronchioles
o Some primitive alveoli
o Differentiation of pneumocytes
 Type 1 – Gas exchange
 Type 2 – Surfactant production from week 20


What is alveolar period?

o Late fetal  8 years
 95% of Alveoli are formed post-natally


How do the lungs prepare for birth?

Breathing’ movement
 Conditioning of the respiratory musculature
o Fluid filled
 Crucial for normal lung development


What is main part of brain development?

Corticospinal tract


When does corticospinal tract begin to develop?

4th month


Why can't babies move properly at birth?

o Myelination of the brain only beings in the 9th month
 Corticospinal tract myelination incomplete at birth, as evidence by increased infant mobility in the 1st year


When does movement begin?

Week 8


How much of body weight is brain at birth?



Give four changes which occur in brain during foetal period

o Cerebral hemisphere becomes the largest part of the brain
 Gyri and sulci form after 5 months as the brain grows faster than the head
o Histological differentiation of cortex in the cerebrum and cerebellum
o Formation and myelination of nuclei and tracts
o Relative growth of the spinal cord and vertebral column


In what order do senses develop

Hearing and taste mature before vision. The organ of corti in the inner ear is well developed in the fetus at 5 months, but the retina is immature at birth.


What is quickening?

o Fetal movements can be seen by USS at Week 8
o Maternal awareness of fetal movements from Week 17 onwards


What is the use of assessing foetal movements

o Low cost, simple method of ante-partum fetal surveillance
o Reveals fetuses that require follow-up


What is the significance of foetal heart rate?

Bradycardia associated with foetal demise


When is ascent of kidneys complete

Week 10


Outline kidney development

o Fetal kidney function begins in week 10
 Functional embryonic kidney is the Metanephros
o Renal pelvis, calyces etc present by week 23
o Histological differentiation of cortex and medulla almost complete by 8 months
o Fetal urine is a major contributor to amniotic fluid volume
o Fetal kidney function is not necessary for survival during pregnancy, but without it there is oligohydramnios.


How often do bladder fill and empty?

o Bladder fills and empties every 40 – 60 minutes in the fetus (seen on USS)


What is the threshold of viability?

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


What is respiratory distress syndrome

o Often affects infants born prematurely
o Insufficient surfactant production
o If pre-term delivery is unavoidable or inevitable
 Glucocorticoid treatment (of the mother)
 Increases surfactant production in the fetus


Give six techniques to assess foetal development

o Ultrasound Scan
o Doppler ultrasound
o Non-Stress Tests (NST)
 Monitors hear-rate changes associated with fetal movement
o Biophysical profiles (BPP)
 5 measured variables
o Fetal movements kick chart


When is a foetus regarded as having growth restriction?

If its weight is below the 10th percentile for gestational age


Give two types of growth restriction

Symmetrical growth restriction
Asymmetrical growth restriction


What is symmetrical growth restriction?

 Growth restriction is generalised and proportional


Asymmetrical growth restriction

 Abdominal growth lags
 Relative sparing of head growth
 Tends to occur with deprivation of nutritional and oxygen supply to fetus


Why is estimation of foetal age important?

It is important to distinguish between a fetus born prematurely and one born full term but small.


Give two methods of dating a pregnancy?

o Fertilisation age

o Age since mother’s Last Menstrual Period (LMP)


Give problems with
o Fertilisation age

o Age since mother’s Last Menstrual Period (LMP)

o Fertilisation age
 Use of calendar months may cause inaccuracies
o Age since mother’s Last Menstrual Period (LMP)
 Irregular cycles may cause confusion


Give five developmental criteria of foetus

o Crown-Rump (CR) length
 Used in T1
o Foot length
o Biparietal diameter of head
 Used in T2/T3
o Weight after delivery
o Appearance after delivery


What is another way of measuring foetal age?

Symphysis – Fundal height
o Distance between symphysis pubis to top of uterus (fundus)
o Measured with a tape measure


Give three problems with Symphysis – Fundal height

 Number of fetuses can cause variation
 Volume of amniotic fluid can cause variation
 The lie of the fetus can cause variation


What is use of daily rhythmns?

A fetus has daily rhythms of heart rate, breathing and activity. Heart rate variability is a good index of developing control systems.


What is oligohydraminos?

o Too little
o Placental insufficiency
o Fetal renal impairment
o Pre-eclampsia


PWhat is polyhramnois?

o Too much
o Fetal abnormality
 E.g. inability to swallow
 Structural – blind-ended oesophagus
 Neurological – unable to coordinate swallowing movements


What is quickening?

o Maternal awareness of fetal movements from Week 17 onwards
o Low cost, simple method of ante-partum fetal surveillance
o Reveals fetuses that require follow-up


Classify birth weights

o < 2,500g = Growth Restriction
o 3,500g = Average
o > 4,500g = Macrosomia
o Maternal diabetes


Describe the effects of poor nutrition in early pregnancy

o Neural tube defects
 E.g. DiGeorge Syndrome


Describe the effects of poor nutrition in late pregnancy

o Asymmetrical Growth Restriction
 Subsequent oligohydramnios


Describe foetal circulation before birth

o Oxygenated blood enters fetus via the Umbilical Vein from the placenta
o Oxygenated blood bypasses the liver via the Ductus Venosus
o Oxygenated blood passes from the RA  LA via the Foramen Ovale
o Blood passes from the pulmonary artery  Aorta via the Ductus Arteriosus
o Deoxygenated blood returns to the placenta via the two Umbilical Arteries


Why is resistance so high in the lungs?

Hypoxic Pulmonary Vasoconstriction.


Describe changes in foetal circulation after birth

The infant takes its first breath, removal Hypoxic Pulmonary Vasoconstriction and greatly reducing the resistance of the lungs.
o Greater venous return to LA
 Pressure in LA > RA
 Closure of the Foramen Ovale
 (Minutes)
o Increased O2 saturation of blood and decreased [Prostaglandins] (placenta has been removed)
 Constriction of Ductus Arteriosus
 Constriction of Umbilical Artery
 (Hours)
o Stasis of blood in Umbilical Vein and Ductus Venosus
 Clotting of blood
 Closure due to subsequent fibrosis
 (Days)


Give two main roles of aminiotic fluid

Mechanical protection
Moist environment so foetus does not dehydrates


How much amniotic fluid at
8 weeks
38 weeks
42 weeks

o ~10ml at 8 weeks
o ~1 Litre at 38 weeks
o Falls to ~300ml at 42 weeks


How is amniotic fluid produced early in pregnancy?

 Formed from maternal fluids
 Fetal extracellular fluid by diffusion across non-keratinised skin


How is amniotic fluid produced later in preg?

Turnover via foetus


What do amniotic fluid contain? What is it useful?

Cells from foetus and amnion.
It included a variety of proteins, and if sampled via a Amniocentesis, can be diagnostically useful.


How much urine does foetus produce at 25 weeks

25 weeks - 100ml
term - 500ml


Why does foetus swallow amniotic fluid? What does it form?

Absorbs water and electrolytes
Debris accumulates in foetal gut and forms meconium


What is bilirubin formed by? Who conjugates it?

Haemoglobin breakdowwn in foetus and mother
Conjugated by mother


What problems can occur with bilirubin in foetus? What can cure it?

o Neonate may become jaundiced if conjugation does not establish quickly
 Liver has never had to conjugate bilirubin before during pregnancy, so it takes a little bit of time for the liver to kick in
 Exposure to light (phototherapy) stimulates the liver to begin conjugation


What is the driving force for oxygen diffusion from mother to foetus?

Oxygen diffuses across the placenta from maternal blood across a thin barrier
The driving factor for this is the gradient of partial pressures between maternal and umbilical blood, as the placenta has a large area for and low resistance to diffusion.
o Maternal pO2 increased
o Umbilical venous pO2 must be must lower


What is dangerous about foetal hypoxia?

Fetal oxygen stores are very low (about 2 minutes worth), which can be a problem in labour, particular if the problem involves the placenta. Contraction of the myometrium can compress placenta blood vessels.


What is a good indicator for foetal O2?

Foetal heart rate is a good indicator of foetus O2 saturation.


What is normal foetal pO2?

o Fetal pO2 is 4kPa
 Normal arterial pO2 in adults is 13.3kPa


What is different about foetal haemoglobin?

o Fetus has different haemoglobin, without beta chains, which is better at these lower partial pressures of O2.
 The higher affinity of fetal haemoglobin ‘sucks across’ the O2
 Fetal Haemoglobin is 70% saturated at 4kPa
 Adult Haemoglobin is 45% saturated at 4kPa


What is double bohr effect?

An increase in pCO2 or [H+] concentrations results in Haemoglobin losing affinity for and releasing more oxygen. This is called the Bohr Effect. This happens both in the maternal and fetal blood, so is termed the Double Bohr Effect.


What is CO2 transfer moderated by?

Placental CO2 therefore needs to be facilitated by lowering maternal pCO2. This is achieved by Hyperventilation, stimulated by Progesterone.