Fetal Physiology Flashcards
What does the umbilical vein carry?
Oxygenated blood
What do the umbilical arteries carry?
Deoxygenated blood
Compare the partial pressure of O2 of fetal blood to maternal
Lower partial pressure of O2 in fetal
Allows gradient of transfer from mother to fetus
How can a pregnant mother develop physiological respiratory alkalosis?
Progesterone causes physiological hyperventilation
Where does materno-fetal exchange occur?
At the placenta
What facilitates the movement of O2 from maternal to fetal blood?
- relative partial pressure difference
- higher affinity of fetal haemoglobin for O2
- double Bohr effect
How does fetal haemoglobin have a higher affinity for oxygen than maternal Hb
HbF doesnt bind 2,3-BPG as effectively as HbA
Composition of fetal haemoglobin
2 alpha subunits
2 gamma subunits
Describe the double Bohr effect in materno-fetal gas exchange
Maternal:
- CO2 passes into intervillous blood > pH decreases
- decreasing affinity of maternal Hb for O2
Fetal:
- relative decrease in CO2 on fetal side > pH increases
- increased affinity of fetal Hb for O2
Outline fetal circulation
- receives oxygenated blood from mother via placenta in umbilical vein
- lungs are non function > by passes lungs
- returns to placenta via umbilical arteries
Describe the double Haldane effect in materno-fetal gas exchange
Mother:
- as maternal Hb gives up O2, it can accept more CO2
Fetal:
- as fetal Hb gives up more CO2, it can accept more O2
What is fetal bradycardia a sign of?
Fetal distress
What are the shunts in fetal circulation?
Ductus venosus
Foramen ovale
Ductus arteriosus
What does ductus venosus do?
Between umbilical Vein and IVC
Bypasses the liVer
What does foramen ovale do?
From RA to LA
Bypasses right ventricle + lungs
What does ductus arteriosus do?
Between pulmonary trunk + aorta
Bypasses lungs
What does chronic hypoxaemia in fetus cause?
Growth restriction
Reduced Fetal movements
Fetal response to hypoxia
- fetal heart rate slow in response to hypoxia
- reduces O2 demand
- fetal chemoreceptors detect decreased pO2 or increased pCO2 > vagal stimulation > bradycardia
Function of amniotic fluid
Protection
Contributes to development of lungs
What is amniocentesis?
- Aspiration of amniotic fluid for analysis
- used for fetal karyotyping e.g. diagnosis of Down’s syndrome
Signs of fetal distress
Meconium staining
Fetal bradycardia
How is amniotic fluid produced?
- hydrostatic pressure pushes water out from fetus’ skin (transudative)
- then composed of fetal urine from week 9
How is amniotic fluid recycled?
- fetus inhales amniotic fluid (practicing breathing movements) > helps production of lungs (surfactant)
- fetus swallows amniotic fluid > enters fetal GI tract > meconium
Composition of amniotic fluid
- 98% water
- Plus electrolytes,creatinine, urea, bile, glucose…
What is a sign that a baby has passed meconium in utero?
Water breaking discolouration
(Meconium in amniotic fluid)
What is intermittent auscultation?
- listening to heart rate for 1 minute using Doppler every 15 mins in first stage
- every 5 mins in second stage
Two methods of intrapartum monitoring during labour
Intermittent auscultation
Cardiotocograph
When is a cardiotocogrpah used?
Higher risk pregnancies
e.g worry for fetal wellbeing, if mum had previous C section or has diabetes
What is physiological jaundice in newborns?
Baby can appear jaundice due to delay in newborn ability to conjugate + excrete bilirubin
How is placental circulation investigated?
Doppler ultrasound scan
