Flashcards in 9.1 Deck (42)
Define the pre-embryonic, embryonic and fetal periods.
PE: Fertilisation --> 2 weeks
E: 3 --> 8 weeks
F: 9 --> 38 weeks
What is a crown rump length and how does it change in pregnancy?
Measurement of human embryo length from top of head to bottom of buttocks.
Increases rapidly in the pre-embryonic, embryonic and early fetal periods.
Describe weight gain of fetus during pregnancy?
Slow at first but increases rapidly in the mid and late fetal periods.
At what week is the head half of the crown rump length.
What proportion of the crown rump length is the head at healthy birth?
Approx 1/4 of body
What process occurs as an early fetus, late fetes and embryo in terms of weight gain?
Embryonic period - Intense morphogenesis and differentiation with little weight gain and placaental growth most significant
Early fetus - protein deposition
Late fetus - adipose deposition
When does the specialisation of the lungs occur? When do they become viable? Implication
Embryonic development only creates airway, no gas exchange parts.
Specialisation for function in fetal period
Viable only after 24 weeks
--> Pre term survival
What are the 4 stages of development of the respiratory system? Name and period.
Pseudoglandular stage: 8 - 16 weeks
Canalicular: 16 - 26 weeks
Terminal Sac stage: 26 - Term
Alveolar period: Late fetal - 8 years
What occurs in the pseudo glandular stage?
Duct systems form within bronchi pulmonary segments created during the embryonic period.
What occurs in the canalicular stage?
Formation of respiratory bronchioles
- Budding from bronchioles
Some terminal sacs
May be viable
What occurs in the terminal sac stage?
Terminal sacs begin to bud from the respiratory bronchioles
Some primitive alveoli
Differentiation of pneumocytes
Type 1 - gas exchange
Type 2 - surfactant production
When do most alveoli form?
How are the lungs prepared to assume full birder immediately after birth?
Breathing movement - conditioning of respiratory musculature.
Fluid filled - crucial for normal lung development.
What are corticospinal tracts required for and when do they begin to form?
Required for coordinated voluntary movement and begin to form in 4th month.
When does myelination of the spinal cord and the brain begin?
Spinal cord - 20th week
Brain - 36th week (9th month)
When does the fetus begin to move?
What changes occur in the brain during the fetal period?
Cerebral hemispheres become largest part of brain.
Gyri and sulci form after 5 months as brain grows faster than head.
Differentiation of cortex in cerebrum and cerebellum
Formation and myelination of nuclei and tracts
Relative growth of the spinal cord and vertebral column.
At what week is maternal awareness of fetal movement?
What senses mature first?
Hearing and taste before vision.
Organ of corgi developed at 5 months, tertian immature at birth.
When is the definitive fetal heart rate achieved?
After 15 weeks.
When is the ascent of the kidneys complete and when does fetal kidney function begin?
When are the renal pelvis and calyces present?
What is a major contribution of amniotic fluid
What occurs in the absence of fetal kidney function?
When is viability first a possibility
After 24 weeks when the lungs have entered the terminal sac stage.
When the brain is sufficiently mature to control body functions
Describe respiratory distress syndrome.
Affects infants born prematurely
Insufficient surfactant production
Glucocorticoid treatment of mother increases production of surfactant in fetus (if pre-term delivery is unavoidable).
How can fetal development be assessed?
Non stress Test - monitors heart rate changes associated with fetal movement.
Fetal movements kick chart
What are the 5 measured variables in biophysical profiles?
Fetal movement - nervous/MSK
Fetal heart rate - Resp
Amniotic fluid volume - Urinary/GI
Fetal tone - nervous/MSK
Fetal breathing - Resp/MSK/nervous
When is a fetus regarded as having a growth restriction?
Weight is below 10th percentile for gestational age.
What is a symmetrical growth restriction
Growth restriction is generalised and proportional.
What is an symmetrical growth restriction? What causes this?
Abdominal growth lags
Relative sparing of head growth
Occurs with deprivation of nutritional and oxygen supply to fetus.
How can duration of pregnancy be measured?
Fertilisation age - use of calendar months may cause inaccuracy
Age since mothers last menstrual period - irregular cycles may cause confusion.
What criteria can be used to measure fetal age?
T1 - Crown rump length
T2/3 - Biparietal diameter of head (distance between parietal bones) with abdominal circumference and femur length
Weight after delivery
Appearance after delivery
What is symphysis-fundal height?
Distance between pubic symphysis to top of uterus (fundus)
Measiured with a tape measure
What can cause variation in symphysis fundal height?
Number of foetuses
Volume of amniotic fluid
Lie of the fetus
What is oligohydramnios and what is it caused by?
Too little amniotic fluid
Can cause: placental insufficiency, fetal renal impairment and pre-eclampsia.
What is polyhydramnios and what is it caused by?
Too much amniotic fluid
Inability to coordinate swallow and blind ended oesophagus.
What are the classifications of birth weights for growth restriction, average and macrosomia?
Less than 2500
More than 4500
What is the effect of poor nutrition during early and late pregnancy?
Neural tube defects E.g. DiGeorge syndorme
Asymmetrical growth restriction and oligohydramnios
Importance of accurate dating
Babies can have low birth weight due to:
How are pregnancy weeks calculated?
From the date of the LMP
Conception weeks + 2 so term is 40 pregnancy weeks