7.1: Fetal development Flashcards
Define the ‘fetal period’ and when it occurs
End of 8th week-term.
Growth and maturation of structures created during the embryonic period, preparing for transition to independent life
How long are the following stages?
a) pre-embyronic
b) embryonic
c) fetal
a) 1-2 weeks
b) 2-8/9 weeks
c) 9-38 weeks
Describe the development occurring during the embryonic period
Organogenetic period: three germ layers -> major organs
Small absolute growth other than placenta
Describe the growth pattern of weight gain. In which stage/period does maximum growth and weight gain occur?
Slow initially -> increases rapidly in mid-late fetal periods first with deposition of protein and later adipose in
subcutaneous and abdominal stores
What is the CRL and what can it be used for? What is its growth pattern?
Crown-rump length; estimates EDD
Increases rapidly in all three periods
What is the metabolic and growth significance of the following stages?
a) embryo
b) early fetus
c) late fetus
a) Morphogenesis and differentiation, small weight gain but sig. placental growth
b) protein deposition
c) adipose deposition
List three things that can be used to perform an ante-natal assessment of the fetus and when they might be used
- 1st trimester: USS
- ~17 wks onwards asking mother if she’s felt fetal movements
- 2nd and 3rd tri: measure uterine expansion (symphysis-fundal height)
When are obstetric ultrasound scans routinely carried out and what two major things can they assess for?
12 and 20 weeks; Fetal growth and anomalies
How would you provide an EDD to a patient?
Provide the one calculated by the scan (even if the woman says it doesn’t line up with her LMP) unless its an IVF
What is the biparietal diameter? What can it be used for and when?
Distance between parietal bones of the fetal skull, used with other measurements (i.e femur length, abdominal circumference) to date pregnancies and determine any anomalies in T2 and T3
What is the general classification of birth weights (average, growth restriction and macrosomia)?
Average 3kg
Growth restriction <2.5 kg
Macrosomia >4.5 kg
Name 3 general reasons for a baby having a low birth weight
- Premature
- Constitutionally small
- Growth restriction
Why is it important for a baby to be delivered at ‘40+12’ weeks
- Placental bloodflow becomes more compromised
2. Increased risk of stillbirth
When does the respiratory system develop in relation to other systems? When is the bronchopulmonary tree formed and when does functional specialization occur?
Later
- Embryonic development creates the bronchopulmonary tree
- Functional specialization occurs in the fetal period
What does the lung/respiratory bud arise from and what structure is responsible for separating the trachea and esophagus?
Resp diverticulum (pouches off the esophagus) -> lung bud
Tracheoesophageal septum
What is a complication of a tracheoesophageal fistula, how and how might this be recognized once the baby is born?
Amniotic fluid doesn’t pass normally through GI tract -> accumulates in lungs -> polyhydramnios
Can make breathing difficult
Where does gas exchange occur before the baby is born and why? What ‘bodily preparations’ are made in the fetus to assist the lungs in taking over?
Conducted at the placenta (as the developing lungs are fluid-filled, but lungs must be prepared to assume the full burden at birth). The respiratory musculature is pre-conditioned so the baby undergoes “breathing movements” before it is born
What are the fetal implications when the mother has anhydramnios?
Lack of amniotic fluid
- > underdeveloped baby lungs
- > baby can’t move around comfortably -> may develop contractures
What determines the ‘threshold of viability’ of how early a baby can be delivered?
Determined by whether lungs have entered TERMINAL SAC stage of development (sufficiently developed to sustain life)
*baby should also be >5kg
What causes respiratory distress syndrome and what can be given to prevent this?
Premature birth -> insufficient surfactant produced.
If pre-term delivery is unavoidable: give dexamethasone injections to increase surfactant production
What is the functional fetal kidney called? When does it begin functioning and what happens if it is dysfunctional?
Metanephros begins functioning at week 10,
Dysfunctional: Oligohydramnios occurs as fetal urine is a major contributor to amniotic fluid volume
What abnormalities is oligohydramnios suggestive of?
- Reduced renal function
- Placental insufficiency; i.e pre-eclampsia: blood is redistributed to fetal brain rather than the abdomen and kidneys -> poor urine output
What two things must be checked if a woman presents with oligohydramnios?
- Ensure fetal growth isn’t restricted (i.e if cause relates to placental insufficiency)
- Check membrane hasn’t been ruptured
Why is polyhydramnios associated with diabetic moms?
Abundant glucose -> baby grows and pees more
Name 3 potential complications for birth when the mother has polyhydramnios
Excessive pressure …
- > Placental rupture
- > uterus stretches quicker -> contracts early -> early labour
Excessive fluid…
- > baby can move more freely in uterus -> baby may be in abnormal position when water breaks
- > Gushing pressure -> baby limb (still attached) and cord can come out of cervix with water
When does the CNS develop in relation to other systems? Name four major structural CNS changes that occur
First to begin and last to finish
- Cerebral hemisphere becomes largest part of brain
- Histological differentiation of cortex in the cerebrum and cerebellum
- Formation and myelination of nuclei and tracts
- Growth of spinal cord and vertebral column
How do fetal sensory and motor systems develop?
*sensations, pain and movement
Sensory: hearing and taste mature before vision
Ascending tracts for pain are present but not myelinated at 19 weeks
Fetal movements can be detected by USS at 8 weeks (repertoire of movements develop to help baby “practice” for postnatal life, i.e suckling, breathing, etc)
Name 5 tests that can monitor changes of the fetus’ anatomical and physiological parameters
- Ultrasound
- Fetal movements kick chart
- Doppler ultrasound
- Non-stress tests; NST monitors HR changes associated with fetal movements
- Biophysical profiles
When is a fetus regarded as having ‘growth restriction’? What are the two main types of growth restriction?
When their estimated weight is below the 10th percentile for their gestational age
- Symmetrical: growth restriction is generalized and proportional
- Asymmetrical: abdominal and head growth lags
How might you determine the duration of the pregnancy? (2 things)
Fertilization age, LMP
List 5 measurements/predictions that can be made in utero by ultrasound
CRL, foot length, biparietal diameter, weight and appearance after delivery
What is the symphysis fundal height and what can it help determine?
Distance between symphysis pubis to the top of the uterus (i.e fundus).
A lag suggests intrauterine growth restriction
Briefly describe the four histological stages of lung development
- Pseudoglandular: 8-16 weeks, duct system forms up to terminal bronchioles
- Canalicular: 16th-26th weeks, bronchioles bud off, some terminal sacs, more vascular and pseudostratified ciliated columnar epithelia are forming
- Terminal Sac: 26 week- Term: surfactant formed, many terminal sacs and some primitive alveoli
- Alveolar period: last weeks of pregnancy - 8 years, alveoli formed
What happens to the fluid within the fetus’s lungs when it’s born?
Squeezed out in normal vaginal delivery, remaining is absorbed
Name three defects/disorders associated with polyhydramnios
Esophageal or duodenal atresia, CNS abnormalities
