Fetal Circulation and Adaptation to Extra Uterine Life

• Leads from the umbilical cord to the underside of the liver and carries blood rich in oxygen & nutrients. 

• It has a branch which joins the portal vein & supplies the liver. 

• Connects the umbilical vein to the inferior vena cava & shunts blood away from the liver
• About 50% of this blood enters the inferior vena cava through the ductus venosus, & bypasses the liver (not needed)
• Blood mixes with oxygenated blood in the inferior vena cava returning from the fetal lower body and limbs
• The remainder passes through the liver & enters the inferior vena cava through the hepatic veins (blood vessels which transport the liver's deoxygenated blood and blood which has been filtered by the liver (this is blood from the pancreas, colon, small intestine, and stomach) to the inferior vena cava)
• Streams of blood do not mix completely

• Temporary opening between the atria. 

• Shunts blood from the right to the left atrium of the heart. 

• So the majority of the blood entering the right atria passes across to the left atrium

• The reason for this diversion is that the blood does not need to pass to the lungs since it is already oxygenated. 

• Hole in the heart

• Leads from the bifurcation (division into two) of the pulmonary artery to the descending aorta entering it just beyond the point where the subclavian and carotid arteries leave

• Shunts blood from the pulmonary artery to the aorta

• allows majority of blood to bypass the lungs (no great need)

• These branch off the internal iliac arteries and become the umbilical arteries when they enter the umbilical cord. 

• They return blood to the placenta for replenishment

Where the warm environment is stable 

• Protected by fluid 

• Oxygenation without pulmonary function 

• Nourishment without gastric function 

• And no heat is produced 

• Whereby the fetus manoeuvres the hazards of the birth canal 

• And leaves the sheltered environment of the uterus 

• To adjust rapidly to extra uterine life 

• Fetal Carbon dioxide levels raised 

• Oxygen levels lowered 

• Compression of chest wall – lung fluid expelled. 

• External stimuli – temperature from 37 – 21 degrees – baby gasps. 

• Baby external stimuli – by touch, light, noise. 

• Most breathe or cry within 60-90 seconds. 

• Respiration 40 – 60 per minute

• That first breath inflates the lungs and generates a high negative intrathoracic pressure to maintain lung inflation. 

• After first breath a lower pressure required to inflate lungs as presence of surfactant reduces surface tension. 

• Surfactant prevents the collapse of the alveoli once inflated. 

• Respiration can be irregular / abdominal / apnoea for short periods.

• With increasing oxygenation the pulmonary vascular resistance (pressure) reduces & this causes the closure of the ductus arteriosus. 

• Increased blood volume from the lungs returns to the heart, thereby increasing the pressure in the left atrium – this assists in closing the Foramen Ovale. 

• All the other temporary structures close and eventually become ligaments

• Soon after the baby’s birth, the exposure of the umbilical cord to the ‘outside’ birth environment and the associated drop in temperature, instigates a physiological process which causes the Wharton’s jelly to swell and compress the blood vessels buried within it. 

• This process creates a natural ‘physiological’ clamping effect that curbs the flow of blood, and, where it is allowed to continue without intervention, will take between 5-20 minutes to completely halt umbilical blood flow

• debate on whether or not there should be a delay in the cord clamping so baby can receive as much fetal blood as possible. 

• NICE (2007) recommend Active management of the 3rd stage which includes early clamping.

• Once the baby has made the transition, in order to maintain effective oxygenation: 

• Air passages must be clear 

• Adequate respiratory exchange must take place in the alveoli 

• Circulation must be adequate to transport oxygen to the vital centres 

• The respiratory centre must be active & not suppressed by drugs

• Healthy newborns utilize glucose to assist with the transition. 

• This provides the energy to tolerate the birth process & the effort of initiating the first breath. 

• Then uses ketones & lactates to produce energy. 

• Some newborns are more at risk of developing hypoglycaemia (low blood sugar) than others:

• Who were born early, have a serious infection, or needed oxygen right after delivery
• Whose mother has diabetes (these infants are often larger than normal)
• With low thyroid hormone levels (hypothyroidism)
• Who have certain rare genetic disorders
• Who have poor growth in the womb during pregnancy
• Who are smaller in size than normal for their gestational age

• Term neonate – digestive system ready to receive milk. 

• Pass meconium within 24hours. 

• Bowel movements change as feeding becomes established