7 - fetal growth and development Flashcards
(33 cards)
what is the fetal period?
growth and physiological maturation of the structures created during the shorter embryonic period
period involving preparation for the transition to independent life after birth
what are the stages of prenatal development?
pre-embryonic: first 2 weeks
embryonic: 3rd week - end of the 8th week
fetal period: start of the 9th week to birth
when are pregnancy weeks calculated from?
date of LMP (last menstrual period) - so this is conception weeks + 2
what happens to growth and weight in the fetal period?
they accelerate
growth: CRL increases rapidly in pre-embyonic, embryonic and early fetal periods
weight: gain is slow at first, then increases rapidly in mid- and late- fetal periods
what causes weight gain during the different stages of prenatal development?
embryo: intense morphogenesis and differentiation - little weight gain - placental growth most significant
early fetus: protein deposition
late fetus: adipose deposition
how do body proportions change during the fetal period?
at 9 weeks the head is about half crown-rump length
after this the body length and lower limb growth accelerates
what are the ante-natal assessment of fetal well-being?
- mother - fetal movements
- regular measurements of uterine expansion (symphysis fundal height)
- ultrasound scan
what is the symphysis fundal height?
measured in cm from the pubic symphysis to the top of the uterus
what are the advantages of USS?
- safe
- can be used early to calculated age and rule out ectopic pregnancies, number of fetuses
- routine from 20 weeks
what are the methods of estimation of fetal age?
LMP - inaccuracy
development criteria - allows accurate estimation of fetal age
what techniques are used to assess fetal development?
- crown rump length
- biparietal diameter
- abdominal circumference and femur length
- 3D or 4D USS
what is crown rump length?
- measured between 7 and 13 weeks to date pregnancy and EDD
- scan in T1 - less reliable in T2 or T3
what is biparietal diameter?
distance between the parietal bones
used in combination with other measurements to date pregnancies in T2 and T3
what is abdominal circumference and femur length?
used in combination with BPD for dating growth and development
used for anomaly detection
3D and 4D USS
new technology
not replaced standard USS
what are the classifications of birth weights?
3500g = average
< 2500g = growth restriction
> 4500g = macrosomia - maternal diabetes
what are the reasons why babies can have low birth weights?
- premature
- constitutionally small (small mum)
- suffered growth restriction
what happens to respiratory development in the embryonic and fetal period?
embryonic period: bronchopulmonary tree develops
fetal period: functional specialisation
what is the initial respiratory bulge called?
respiratory diverticulum
what is the septum that divides the respiratory and GI tract?
tracheoesophageal septum
what are the stages of respiratory development and during which weeks do they occur?
weeks 8-16: PSEUDOGLANDULAR STAGE
weeks 16-26:
CANALICULAR STAGE
weeks 26 - term:
TERMINAL SAC STAGE
describe what happens during the different respiratory stages of growth
PSEUDOGLANDULAR:
budding and branching of the bronchioles starts
CANALICULAR:
branching that forms respiratory bronchioles (still no alveoli)
TERMINAL SAC STAGE:
terminal sacs develop at the ends of the respiratory bronchioles at approx week 26 to term.
at this point type I and II pneumocytes form and start to make surfactant
what happens to the lungs during T2 and T3?
gas exchange still occurs at the placenta
- breathing movements - conditioning of the respiratory musculature
- fluid filled - crucial for normal lung development
what is fetal viability and what is it determined by?
dependent on whether or not the pneumocytes are present.
without these cells gas exchange can not occur and the lungs will not be making surfactant and so is incompatible with life - has implications on termination of pregnancy and premature delivery
