Fetal Development/growth and the Placenta Flashcards
Describe the structure of the placenta and how substances are moved between the mother and the fetus
Maternal spiral arteries and veins
-substances diffuse from the villi basal plate =(intervillous space)=> chorionic villi
1 umbilical vein => fetus => 2 umbilical arteries
Blood does not mix
Describe the structure of the early spiral arteries
What are the 2 methods of substance transfer
Initally histitrophic
-spiral arteries blocked by trophoblastic plug
Becomes haemotrophic
-plug removed, mouth expands to accommodate more blood
Describe how
- CO2
- Glucose
- FA
- AA is trasnported
CO2
-diffuses across syncytiotrophoblast, CA buffered
Glucose
-GLUT1 across STB
FA
- LPL breaks down TAG in LP => FA
- transported to FATP bound to FABP
AA
- NaAAcotransport, nonessential, essential AA exchange
- Na, Cl cotranport
How is fluid homeostasis maintained in the fetus
Maintained by placenta, fetal membrane
- kidneys provide dilute urine (immature ADH)
- bladder fills and empties every 20-30mins
What is found in the amniotic fluid
How is amniotic fluid homeostasis maintained
Urine Amniotic membrane secretions Fetal lung secretions Saliva Fetal and amniotic cells
Fetus swallows fluid from wk12 onwards
How doe the GI system develop in the fetus
-digestive enzymes, when are they found from
-digestive hormones, where and when are they found from
When is it formed by
Formed by wk19
Digestive enzymes
-present by wk9, mature at term
Gastrin motilin, somatostatin
- regulate growth and dev
- gut synthesised, mature by wk24
Describe how glucose homeostasis is maintained
- where does glucose come from
- how is it used
- where does the insulin come from
Dependent on placental transfer
- glycogen storage in fetal liver
- not capable of gluconeogenesis
Fetal insulin and IGF
- lipogenesis
- anabolic, anticatabolic effects for growth
Describe the physiological control of the fetal heart
HR affected by ANS control (PNS dominated)
- NA/A
- chemo/baroceptors
Describe the circulatory route of blood from the placenta
Describe the fetal haemoglobin and its characteristics
Placenta => 1 umbilical vein => ductus venosus (bypass liver) => foramen ovale (bypass pulmonary circulatotion) => ductus arteriosus (bypass lungs) => 2 umbilical arteries
HbF
- increased O2 affinity, [HbF]
- decreased PO2
HbA
-increases from wk28
Describe the fetal hypoxic response
Decreased HR Decreased cerebral resistance Increased umbilical artery resistance Increased flow to heart, adrenals Decreased flow to kidneys => oligohydramnios
Describe the cells in the lungs and their functions
T2 alveolar cells secrete surfactant from wk24 => decrease alveolar surface tension
-PL, C, protein
T1 alveolar cells
What is neonatal resp distress
What is the pathophysiology
How would you manage this
Not enough surfactant
Decreased compliance, alveolar collapse
Increased work to breathe
Exogenous surfactant
-synthetic/modified natural
Cortisol
-stimulate lung dev and surfactant prod
How does -umbilical clamping -inspiration -secretions change at delivery
Umbilical clamping
-decreased RA pressure, FO closes
Inspiration
- VD of pulmonary arteries => decreased R
- decreased F via FO, DA
Secretions
- lung secretions decrease
- surfactant increases
How is placental transfer used in the production of fetal and maternal hormones
Maternal cholesterol
Converted to pregnenolone
-fetus converts this into DHA, DHAS
-can be converted into types of estrogen for maternal use
What are the 3 stages of embryo growth
-what are the main characteristics
Stage 1 (4-20wk) -hyperplasia, rapid mitosis, increase in DNA
Stage 2 (21-28)
- hyperplasia and hypertrophy
- declining mitosis but cell size increases
- greatest weight gain here
Stage 3 (29-40)
- hypertrophy
- rapid increase in cell size
- accumulate fat, muscle, connective tissue
- greatest variation in weight here
What is appropriate for gestational age
Following the expected trends in weight as gestational age increases
What is fetal growth restriction
- what are the short term consequences
- what are the long term consequences
Growth doesn't follow expected trend Pathological restriction/IUGR -stillbirth -seizures -ICU admission -hypothermia, hypoglycaemia
Long term impact
- CHD, HT
- T2D, strokes
What does it mean to be small for gestational age
- what are the 2 main types
- management
<3-10th cent
Following trends in weight but below estimations consistently
Symmetrical SGA - prolonged poor growth from early pregnancy
- healthy, normal
- chromosomal, congenital issues
- alcohol, cigarettes, drugs
- TORCHZS
- malnutrition
Assess for pathological cause, infections
Monitor growth frequently
Asymmetrical - placenta fails to provide adequate nutrition late in pregnancy
- placental insufficiency, PET
- alcohol, cigarettes, drugs
- congenital, chromosomal
Assess for absent end diastolic flow in umbilical circulation with Doppler
Monitor growth frequently
Consider early delivery
How would you detect, prevent and manage SGA
Detection and prevention
- decreased PAPPA, high uterine flow resistance (poor placental function)
- aspirin, monitor growth, decrease PET risk
Management
- if FGR=> early delivery with steroids
- if SGA=> induce before term
How would you interpret a fetal doppler for the
- umbilical artery
- MCA
Fetal doppler, judge direction and quality of blood flow
-generates pulsatility index
Umbilical artery
- if line falls under x axis => flow reversed
- if line falls on x axis => no flow at that point
- if pulsatility index increases, blood has to work harder to be moved around
MCA
- if diastole is higher than expected => MCA being prioritised for some reason
- if PI decreases => be worried
What are the possible growth outcomes for twins
- what birth would be low risk
- what births would be high risk
Both grow normally
Both SGA
AGA, FGR => may need to deliver at different times
Low risk
-DC
High risk
- MC
- potential selective IUGR
- potential twin to twin transfusion
What does it mean to be large for gestational age
-what are the causes
-what are the risks
How would you manage this
> 90th centile
Healthy large => large parents
Poorly controlled maternal diabetes
- shoulder dystocia (fat accumulates on shoulders)
- hypoglycaemia (exposed to increased glucose, produces extra insulin
- increased chance of maternal complications
- PPH
- Caesarean may be needed
What are the consequences of shoulder dystocia
Brachial plexus injury
-Erbs palsy
Fractured humerus, clavicle
-Asphyxia, death
When is the earliest that you can detect a fetal heartbeat?
6-7wks
CRL 1-2mm
