L16: fetal development Flashcards
Define the fetal period
Longest period of development
From 9 weeks to term – period of physiological maturation of systems that have been created during the embryonic period (3-8 weeks)
Weight gain accelerates during this time
What is the crown rump length?
Length of the fetus
Measurement increases dramatically in a linear fashion during the pre-embryonic, embryonic and early fetal periods
Useful measurement to use to monitor development particularly in early pregnancy
Describe the pattern of weight gain and growth
Weight gain – initially, the tissue contributing to weight is protein, but later in the fetal period, adipose tissue is developed for metabolic purposes & regulation of heat
Proportion of growth – initially, head forms 50% of the length, but as pregnancy proceeds, limbs and trunk elongate (head forms 25% of length)
How can fetal wellbeing be assessed?
Ask the mother – fetal movements can be felt by the mother at around 20 weeks
Symphysis-fundal height – non-invasive way to assess growth by measuring length from the pubic symphysis to the top of the fundus (at 20 weeks, FH landmark should be roughly at the umbilicus)
Ultrasound scan – can estimate the date of pregnancy, rule out ectopic or identify multiple pregnancy (20 week scan = measures fetal growth by taking specific measurements & assess any developmental abnormalities)
Why might the symphysis-fundal height not correlate to the week of gestation?
1) Polyhydramnios: lot of amniotic fluid, the measurement will be much larger -> swallowing difficulties or excessive urine production
2) Oligohydramnios: measurement can be less due to IUGR or lack of fluid production – normal for the measurement to drop near term
How can you estimate fetal age?
LMP – looking at first day of a woman’s LMP is a relatively easy way to date a pregnancy, however it can be prone to inaccuracy
Developmental criteria – done by comparing USS measurements of the fetus to an average ‘normal’ value based on researched values -> much more accurate
-CRL in early pregnancy, biparietal diameter & abdominal circumference in second and third trimesters
Why might a baby have a low birth weight?
1) Premature
2) Could be constitutionally small eg. because the mother is small
3) May have a growth restriction
(NB: most common cause of macrosomia = poorly controlled gestational diabetes)
Describe the development of respiratory system
Happens relatively late as they are not required for gas exchange until after delivery
Develops as an outpouching of the foregut = bronchopulmonary tree in the embryonic period
Budding and branching of the bronchioles starts in week 8-16 = pseudo-glandular stage
Further branching happens to form respiratory bronchioles in weeks 16-26 = canalicular stage – still not alveoli at this stage
Terminal sacs develops from the ends of the respiratory bronchioles at approximately week 26 to term (only at this point that pneumocytes develop)
How is fetal viability determined?
Determined on whether pneumocytes are present – without those cells, gas exchange cannot occur, lungs are not producing surfactant & it is therefore not compatible with life
Has implications for termination of pregnancy and premature delivery
Pre-term delivery is unavoidable but predictable = can give mother glucocorticoids to help stimulate the production of surfactant in the fetus
What is the average fetal heart rate?
Between 110-160 beats per minute
Important to know when assessing for fetal bradycardia as a sign of fetal distress
Describe the urinary system & amniotic fluid volume
Fetus starts producing urine in the fetal period, however renal function is not being done by the kidney at this stage – removal of waste is managed by the placenta & largely reliant on the maternal renal function for excretion
Amniotic fluid volume – important measure of kidney function in fetus:
1) Oligohydramnios: low volume of amniotic fluid may be due to placental insufficiency/indicate poor renal function in the fetus
2) Polyhydramnios: variation of normal/indicate an issue in the recycling of amniotic fluid
Describe the development of the nervous system
First to start developing & the last to finish – most vulnerable to injury
Coordinated movements require a tract called corticospinal tract, which begins to form in the 4th movement
Myelination of these tracts is incomplete at birth – babies can’t walk or perform other co-ordinated movements until approx. 1 year after birth
Movements that occur in utero = practice for independent life after birth (earliest time a mother can sense the fetus movement = ‘quickening’)
