Fetal circulation

• Fetal circulation

  The fetal circulatory system provides the fetus with nutrients and oxygen while removing waste products and carbon dioxide from fetal circulation, all controlled via the placenta
• Fetal circulation route 1

  Blood from inferior vena cava goes into Right Atrium, through Foramen ovale into Left Atrium, then into Left Ventricle, then out via Ascending aorta
• Fetal circulation route 2

  Blood from superior vena cava goes into Right Atrium, via tricuspid valve to Right Ventricle, then to Pulmonary trunk, via Ductus Arteriosus to Descending Aorta
• Temporary structures in fetal circulation

  • Ductus Arteriosus
  • Foramen Ovale
  • Ductus Venosus
• What the temporary structures become

  • Umbilical vein becomes ligamentum teres
  • Ductus venosus becomes ligamentum venosum
  • Foramen ovale closes and becomes fossa ovalis
  • Umbilical arteries become umbilical ligaments and superior vesicular artery
• Changes at birth

  • Circulatory changes are the most important stages in adaptation to life ex-utero
  • Initiated within 60 seconds of birth but may take weeks to complete
  • Umbilical circulation ceases and lungs expand, causing increased pulmonary blood flow and closure of fetal shunts
  • Obsolete structures cease to function
• Changes at birth - First breath

  1. Lungs expand

  2. Vasodilation of pulmonary vessels

  3. Pulmonary resistance reduced

  4. 90% of blood now passes through pulmonary arteries to lungs

  5. Brief reversal of blood flow through Ductus Arteriosus, which then closes
• Changes at birth - Blood flow

  1. Blood returning through Pulmonary veins into left atrium cause increase in pressure

  2. Cessation of umbilical blood flow causes pressure in right atrium to drop

  3. Pressure on the flap of the Foramen Ovale is reversed, causing it to close
• Why the change

  • In utero, gas exchange occurs via the placenta, not the lungs
  • Temperature, nutrition, excretion controlled by mother
  • Once born, the baby's lungs and organs must immediately begin to function independently
  • Therefore circulatory changes must occur so that all organs are stimulated to function
  • Structures necessary for fetal circulation no longer needed
• Changes at birth - Umbilical circulation

  1. Umbilical arteries are sensitive to touch and become constricted due to pressure, stretching and handling during birth

  2. Vasoconstriction occurs, preventing blood flow from baby to placenta

  3. Umbilical vein remains dilated, allowing placental blood to flow to baby via gravity
• What stimulates a baby to breathe at birth

  • Hypoxia
  • Hypercapnia
  • Light
  • Cold
  • Noise
  • Touch
  • Pain
  • Olfactory
• Factors that assist changes at birth

  • Surfactant - produced by Type II cells in lungs - reduces surface tension and prevents alveoli from collapsing
  • Circulating catecholamines (Epinephrine) - reduce secretion of lung fluid, increase absorption through lymphatic system, increase heart rate and contraction, increase coronary perfusion
• Midwife's role


  Ensure successful transition by maintaining a neutral-thermal environment to enable baby to use minimal energy to stay warm
• When things don't go to plan, neonatal resuscitation is required
• Persistent fetal circulation

  • Closure of the Foramen Ovale is reversible in first few days, with signs being transient cyanotic episodes
  • After a few days, the tissue fuses and cannot be re-opened
  • Hormones released from inflated lungs help constrict the Ductus Arteriosus
  • A "patent ductus" is a serious anomaly
• Persistent fetal circulation


  • Patent Ductus Arteriosus
  • Patent Foramen Ovale
• Factors that affect the transition

  • Antenatal risk factors: PIH/chronic hypertension/PET, Diabetes, Renal disease, Epilepsy, Severe anaemia, Placental insufficiency
  • Intrapartum risk factors: APH, Multiple pregnancy, Instrumental deliveries, C section, Maternal sedation, Prolonged/precipitate labour, Prolonged ROM, Hypertonic uterine contractions, Placental abruption, Cord prolapse