Fetal Growth + Development Flashcards
What is the fetal period?
What occurs during this time?
- From 9 weeks to term
- physiological maturation of structures created in the embryonic period
- period of preparation for transition to independent life after birth
Outline the patterns of growth during development of the fetus
Embryonic period:
- absolute growth is very small, except the placenta
- characterised by intense activity
Fetal period:
- growth + weight gain accelerate
What is the crown rump length?
Length of the fetus
Body proportions in the fetal period
- at week 9, the half is 50% of the crown rumplength
- after, the body length + lower limb growth accelerates
- head makes up 25% of the length at term
How can fetal well-being be assessed?
- last menstrual period (age of fetus + estimate due date)
- ask the mothers (fetal movements)
- symphysis fundal height
- ultrasound scan
When do fetal movements start to happen?
~ 20 weeks
How is symphysis fundal height used to assess fetal wellbeing?
Normal SFH = number of week +/- 2cm
Why may symphysis-fungal height be larger?
- polyhydramnios: if there is a lot of amniotic fluid
- accumulation can happen due to swallowing difficulties or excessive urine production
Why may symphysis fundal height be low?
- intrauterine growth restriction
- oligohydramnios: lack of amniotic fluid production
- normal near term as fetal head engages in the pelvis
What is the 20 week scan used for?
anomaly scan
- screen for fetal anomalies
- determine placental location
- sex of baby
What is the 12 week scan used for?
- dating scan
- determine gestational age
- detect multiple pregnancy
- screening for chromosomal abnormalities
What 2 scans are used in antenatal care?
12 week scan (dating scan)
20 week scan (anomaly scan)
When is the crown rump length used?
Measured between 7 -13 weeks to date pregnancy
In 12 week dating scan
What measurements are used to determine fetal size?
Crown rump length
Biparietal diameter
Abdominal circumference
Femur length
What is the biparitetal diameter measurement?
When is it used?
- Distance between the parietal bones of the fetus
- In 2nd + 3rd trimester
- Used in combination with abdominal circumference
What is the abdominal circumference measurement?
When is it used?
- measures widest part of the abdomen
- in 2nd + 3rd trimesters
- in combination with biparietal diameter + femur length
What measurement is used in the first trimester to help date pregnancy?
Crown rump length
What is the average normal brith weight at term?
~ 3.5 kg
What is macrosomia?
Large baby
>4kg
Birth weight ranges for babies at term
- extremely low birth weight: <1kg
- very low birth weight: 1-1.5kg
- low birth weight: <2.5kg
- average normal: ~3.5kg
- macrosomia: >4kg
Why can babies have a low birth weight?
- premature
- constiutionally small
- suffered growth restriction (associated with neonatal morbidity)
Types of fetal growth restrictions
Symmetrical
Asymmetrical
What is symmetrical intrauterine growth restriction?
What is it due to?
- occurs early on in pregnancy <20 weeks
- abdominal circumference, biparietal diameter + fetal length all proportionally reduced
- due to genetic disorders or TORCH infections
Changes to fetal measurements in symmetrical intrauterine growth restrictions
Abdominal circumference, biparietal diameter + fetal length ALL proportionally reduced
What is asymmetrical intrauterine growth restriction?
What is it due to?
- occurs later on >20 weeks
- abdominal circumference decreased
- biparietal diameter + femur length normal
- due to placental insufficiency e.g. pre-eclampsia
Changes to fetal measurements in asymmetrical intrauterine growth restrictions
- abdominal circumference decreased
- biparietal diameter + femur length normal
Development of the respiratory system in the embryonic + fetal period
- lungs develop relatively late
- embryonic period: only bronchopulmonary tree
- fetal period: functional specialisation
What are the lung development stages?
Every Penguin Can Swim Anywhere
Embryonic
Pseudoglandular
Canalicular
Saccular
Alveolar
What is made in the embryonic stage of lung development?
Only bronchopulmonary tree
What is made in the psuedoglandular stage of lung development?
Terminal bronchioles
- duct system begins to form within the bronchopulmonary segments
What is made in the canalicular stage of lung development?
Respiratory bronchioles
- budding from bronchioles formed in psuedoglandular stage
- start of differentiation of cuboidal cells to type 1 + 2 pneumocytes
What is made in the saccular stage of lung development?
- terminal sac begin to bud from respiratory bronchioles
- differentiation of type I + II pneumocytes > surfactant made
What is made in the alveolar stage of lung development?
- mature alveoli formation
- proliferation + expansion of capillaries, nerves + gas exchange areas
What is fetal viability?
The ability of a fetus to survive outside the uterus
What is respiratory distress syndrome due to?
Insufficient surfactant production
When is the first heat beat of a fetus?
When is definitive fetal heart rate achieved?
5-6 weeks
15 weeks
What is definitive fetal heart rate?
110-160bpm
What is fetal bradycardia a sign of?
Fetal distress
When does fetal kidney function begin?
Week 10
What is oligohydramnios?
What can it be due to?
What could indicate this?
- Low volume of amniotic fluid
- due to placental insufficiency or poor renal function in fetus (poor blood supply)
- Low symphysis-fundal height
What is polyhydramnios?
What can it be due to?
What could indicate this?
- high volume of amniotic fluid
- due to fetal abnormalities (oesophageal atresia), gestation diabetes, fetal anaemia or multiple pregnancies
- high symphysis-fundal height
When does myelination of the brain begin?
9th month
Role of magnesium sulphate during pregnancy
- given to women at high risk of imminent spontaneous preterm brith between 24-29 weeks gestation
- given for fetal neuroprotection e.g. reduces risk of cerebral palsy
Why is the nervous system the most vulnerable to injury during development?
First to start development
Last to finish
What do co-ordinated movements require?
When does this form?
Corticospinal tract
Begins to form in the 4th month
Why are new born babies unable to walk or perform coordinated movements until ~ 1 year?
Myelination of the corticospinal tract is incomplete at birth
When is fetal viability a possibility?
Once the lungs have entered the terminal sac stage of development
>24 weeks
Antenatal managment of respiratory distress syndrome
Glucocorticoid treatment
Boosts lung development > surfactant produced
Neonatal management of respiratory distress syndrome
- nCPAP (nasal continuous positive airway pressure)
- surfactant replacement therapy
- mechanical ventilation
What does a lack of fetal kidney function cause?
Oligohydramnios
What cells produce surfactant?
Type II pneumocytes
What glucocorticoid treatment used for during pregnancy?
How does it work?
- Treatment of respiratory distress syndrome before baby is born
- Boosts lung development > surfactant produced
What are the stages of respiratory development + what develops in each?
Every Penguin Can Swim Anywhere
- embryonic: bronchopulmonary tree
- pseudoglanudlar: terminal bronchioles
- canalicular: respiratory bronchioles + pneumocytes
- saccule: terminal sacs + surfactant produced
- alveolar: alveoli
