Reproduction 9 - Fetal growth & development Flashcards
Describe the pattern of weight gain through embryonic and fetal periods and relate this to aims of the different stages
Weight gain is slow at first, but increases rapidly in the mid and late fetal periods.
Embryo
▪ Intense morphogenesis and differentiation
▪ Little weight gain
▪ Placental growth most significant
Early fetus
▪ Protein deposition
Late fetus
▪ Adipose deposition
What is Crown Rump Length (CRL) and when does it increase the most?
Crown Rump Length (CRL) is the measurement from top of fetus to bottom - increases rapidly in the pre-embryonic, embryonic and early fetal periods.
Body proportions change dramatically during the fetal period. How does week 9 compare with that at birth?
o At week 9, the head is approximately half of the crown rump length
o At birth the health is approximately one quarter of the crown rump length
Which part of the respiratory system develops in the embryonic period?
o Embryonic development creates only the bronchopumonary tree
▪ Airways, no gas exchanging parts
(The lungs develop relatively late, as they are not needed until birth)
When does functional specialism of the lungs occur? Outline the stages
o Functional specialisation occurs in the fetal period
Pseudoglandular Stage: Weeks 8 – 16
o Duct systems begin to form within the bronchopulmonary segments created during the embryonic period
Canalicular Stage: 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
Terminal Sac Stage: Week 26 – Term
o Terminal sacs begin to bud from the respiratory bronchioles
o Some primitive alveoli
o Differentiation of pneumocytes
Alveolar Period
o Late fetal - 8 years
What are the two types of pneumocytes?
▪ Type 1 – Gas exchange
▪ Type 2 – Surfactant production from week 20
During T2 and T3 gas exchange occurs at the placenta. How do the lungs prepare for full function immediately after birth?
o ‘Breathing’ movement
▪ Conditioning of the respiratory musculature
o Fluid filled
▪ Crucial for normal lung development
What are the implications of the relatively late development of the respiratory system?
o Major implications for pre-term survival
▪ Threshold of Viability
▪ Viability is only a possibility after 24 weeks
What tracts are required for coordinated voluntary movements and when do they begin to form?
Corticospinal tracts - 4th month?
What system is the first to start developing and the last to finish?
Nervous system
Describe the neurological changes that occur in the fetus
o Cerebral hemisphere becomes the largest part of the brain
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
The fetal cardiovascular system is arranged to ensure oxygenated blood collected by the umbilical vein at the placenta is circulated around the fetus.
When is the definitive fetal heart rate achieved?
15 weeks - Fetal bradycardia is associated with fetal demise
What can happen if fetal kidneys do not function properly?
Fetal kidney function is not necessary for survival during pregnancy, but without it there is oligohydramnios
Fetal kidney function begins in week 10, what is the name of the functional embryonic kidney?
Metanephros
Where does urine come from/ where does it go?
o Urine is emptied into the amniotic fluid, to be swallowed by the fetus.
o Bladder fills and empties every 40 – 60 minutes in the fetus (seen on USS)
What three factors influence the viability of the preterm neonate?
1) Threshold of Viability - Viability is only a possibility once the lungs have entered the terminal sac stage of development (after 24 weeks).
2) Brain Development - Viability is only possible if the brain is sufficiently mature to control body functions, e.g. breathing.
3) Respiratory Distress Syndrome
o Often affects infants born prematurely
o Insufficient surfactant production
If pre-term delivery is unavoidable or inevitable, how is mother and/or fetus treated?
Glucocorticoid treatment (of the mother) - Increases surfactant production in the fetus
List techniques used to assess fetal development
o Ultrasound Scan o Doppler ultrasound o Non-Stress Tests (NST) o Biophysical profiles (BPP) o Fetal movements kick chart
What is the difference between symmetrical and asymmetrical growth restriction?
o Symmetrical Growth Restriction
▪ Growth restriction is generalised and proportional
o Asymmetrical Growth Restriction
▪ Abdominal growth lags
▪ Relative sparing of head growth
▪ Tends to occur with deprivation of nutritional and oxygen supply to fetus
What are the limitations of using fertilisation age or age since mother’s last period to predict fetal age?
o Fertilisation age - Use of calendar months may cause inaccuracies
o Age since mother’s Last Menstrual Period (LMP) - Irregular cycles may cause confusion
What is the significance of daily rhythms?
A fetus has daily rhythms of heart rate, breathing and activity. Heart rate variability is a good index of developing control systems.
With regard to amniotic fluid, what is oligohydramnios and what is it associated with?
o Too little
o Placental insufficiency
o Fetal renal impairment
o Pre-eclampsia
What is the name for too much amniotic fluid and what fetal abnormalities is it associated with?
o Polyhydramnios o Fetal abnormality ▪ E.g. inability to swallow ▪ Structural – blind-ended oesophagus ▪ Neurological – unable to coordinate swallowing movements
Outline the three categories of birth weight. What is the heaviest associated with?
< 2,500g = Growth Restriction
3,500g = Average
> 4,500g = Macrosomia - Maternal diabetes
