Session 9: Fetal Growth & Development Flashcards
Define fetal period.
Longest period of devopment from 9 weeks and onwards. It is a period of physiological maturation of the structures created during the embryonic period.
Explain what crown rump length is.
The length of the fetus from head to tail.
Why is crown rump length useful?
It can monitor development particularly in early pregnancy.
Why is crown rump length a useful tool to monitor develoment in early pregnancy?
Because it increases dramatically in a linear fashion during the pre-embryonic and early fetal periods.
In early fetal period, what is the main contributing factor to weight?
Proteins (muscle development)
In late fetal period, what is the major contributory factor to weight?
Adipose tissue for metabolism and regulation of heat.
Proportion of the head compared to the rest of the body throughout development.
50% of total length of body early on.
1/4 of the body’s total length at delivery.
Give examples of how you can assess fetal wellbeing.
Ask the mother
Symphysis-fundal height
Ultrasound scan
Why might asking the mother about her experience so far in her pregnancy make it possible for you to assess fetal wellbeing?
Fetal movements start to happen around 20 weeks.
Kicking e.g. is a good sign of fetal wellbeing
Explain what symphysis-fundal height is.
Non-invasive way to assess growth of fetus.
The length from pubic symphysis to the top of the fundus of the uterus
What should the SFH be at 20 weeks?
Roughly at the umbilicus.
How will SFH change after 20 weeks?
The fetal age in weeks should roughly equal the number of cm of this measurement. (28 cm means 28 weeks)
The SFH is not always able to correlate with the weeks of gestation.
Why might the measurement be larger than weeks of gestation?
If there is a lot of amniotic fluid also called polyhydramnios the measurement of SFH will be much larger.
Give causes of polyhydramnios.
Accumulation of amniotic fluid due to swallowing difficulties or excessive urine production.
The SFH is not always able to correlate with the weeks of gestation.
Why might measurement be smaller than weeks of gestation?
Intrauterine growth restriction or a lack of amniotic fluid production called oligohydramnios.
Give examples of use of ultrasound scan (USS).
Date of pregnancy
Rule out ectopic
Identify multiple pregnancy
USS can also in combination with blood tests screen for Down’s syndrome.
What is the ‘20 week scan’?
A measure of fetal growth by taking specific measurements and assess any developmental abnormalities.
Give examples of how you might estimate fetal age.
Last menstrual period (LMP)
Developmental Criteria:
USS measurement
Crown Rump Length
Biparietal diameter
Abdominal circumference
How is pregnancy dated?
From the date of the last menstrual period. This means that a full pregnancy is 40 weeks even though gestation is usually around 38 weeks as ovulation and fertilisation occur around two weeks after LMP.
How can USS be used to estimate fetal age?
By CRL, biparietal diameter, abdominal circumference and femur length and then compare to normal values.
When is CRL useful?
Between 7-13 weeks.
What is biparietal diameter?
Used later in pregnancy which is the distance between the two parietal bones in the fetal skull.
When is biparietal diameter used?
In second and third trimester.
What is abdominal circumference?
It is the widest part of the abdomen.
When is abdominal circumference used?
It is used in the combination with biparietal diameter in second and third trimesters.
Often in combination with femur length as well.
Average weight of fetus.
3500g
Range of normal weight of a fetus.
2500-4500g
Common causes of <2500g baby.
Premature
Constitutionally small
Growth restriction
Common cause >4500g baby.
Poorly controlled gestational diabetes.
Briefly outline the development of the respiratory system.
Happens relatively late as gas exchange isn’t needed until after partum.
1 - Outpouching of foregut to create bronchopulmonary tree in embryonic period.
2 - Budding and branching of bronchioles in fetal period (pseudoglandular stage) 8-16.
3 - Further branching to form respiratory bronchioles (canalicular stage) 16 - 26.
4 - Terminal sac development with alveoli.
Stage 4 is also when Type I and Type II pneumocytes develop in order to produce surfactants.
How can fetal viability be assessed in relation with lung development.
If there are no pneumocytes presents gas exchange cannot occur and lungs do not produce surfactant.
This means that the fetus is not compatible for life.
This can be a complication of premature delivery e.g.
If a pre-term delivery is unavoidable but predictable, how can you resolve the absence of surfactant?
Give the mother glucocorticoids to help stimulate the production of surfactant in the fetus.
What is the average fetal heart rate?
110-160 bpm
Why is this heart rate important to know?
To know what bradycardia is for a foetus.
The fetus starts to produce urine in the fetal period but cannot yet drain it. How is removal of waste managed in utero?
By the placenta and largely reliant on the maternal renal function for excretion.
How can you measure kidney function in the fetus?
By the amniotic fluid volume.
What does oligohydramnios suggest? (think renal)
Low volume of amniotic fluid that can be due to placental insufficiency or indicate poor renal function in the fetus.
What does polyhydramnios suggest? (think renal)
Issue in recycling of amniotic fluid.
E.g. CNS-defect where swallowing isn’t possible.
Congenital abnormalities like a trachea-oesophageal fistula.
If there is an absence of surfactant in the fetal lungs, what might this cause post-partum?
Respiratory distress syndrome.
What is the most vulnerable system to injury during the developmental process?
Why?
Nervous system.
First to start to develop and last to finish.
When is the corticospinal tract starting to develop?
During the 4th month
Why is the corticospinal tract important?
Required for co-ordinated movements.
If the corticospinal tract begins to develop in the 4th month, why can’t a newborn walk until approx. a year after birth?
Because the myelination of the corticospinal tract is incomplete at birth.
When will movement start in utero?
No movement until 8th week.
What is quickening?
The mother becoming aware of the baby moving around
When does myelination of the brain start to occur in the brain?
Around week 36
