Neonatal Circulation After Birth (Postpartum) 

Overview:

After birth, fetal circulation undergoes significant changes as the lungs begin to function, causing the closure of the foramen ovale, ductus arteriosus, and ductus venosus. These closures redirect blood flow to the lungs for oxygenation, with the right side of the heart pumping blood through the pulmonary arteries, and the left side now handling systemic circulation

The transition of a baby's circulatory system right after birth involves several key adaptations to accommodate the shift from fetal to postnatal life. Here's a detailed breakdown: 

1. Removal of the Placenta: 

• Before Birth: The placenta serves as the primary source of oxygen and nutrients for the fetus. 

• Immediately After Birth: The baby is separated from the placenta, marking the end of its reliance on umbilical circulation. 

2. Closure of Fetal Shunts: 

a. Foramen Ovale Closure: 

• In utero, there is a small opening (foramen ovale) between the atria of the heart. 

• Postnatally, the foramen ovale closes as pressure in the left atrium increases due to the initiation of breathing. This prevents the mixing of oxygenated and deoxygenated blood 

  b. Ductus Arteriosus Constriction: 

• The ductus arteriosus, a vessel connecting the pulmonary artery to the aorta, starts to constrict. 

• This constriction is triggered by an increase in oxygen levels and a decrease in prostaglandins, eventually closing off the ductus arteriosus. 

3. Initiation of Breathing: 

• The baby takes its first breath, filling the lungs with air. 

• Oxygen replaces amniotic fluid in the alveoli, promoting the dilation of pulmonary arterioles and reducing resistance in the pulmonary circulation. 

4. Changes in Umbilical Circulation: 

a. Umbilical Arteries Constriction: 

• Umbilical arteries, responsible for carrying deoxygenated blood from the baby to the

  placenta, constrict. 

• Smooth muscle contraction in response to increased oxygen levels and decreased

  prostaglandins leads to the closure of these arteries. 

  b. Clamping of the Umbilical Cord: 

• The umbilical cord is clamped and cut, permanently disconnecting the baby from the

  placenta. 

5. Establishment of Independent Circulation: 

• Transition to Systemic Circulation: 

• The baby's circulatory system transitions from a parallel (fetal) circulation to a series (adult) circulation. 

• The left side of the heart pumps oxygenated blood to the body, while the right side pumps deoxygenated blood to the lungs. 

• Functional Pulmonary Circulation: 

• The pulmonary circulation becomes fully functional as the baby breathes independently. 

• Blood flows to the lungs to receive oxygen before being pumped to the rest of the body. 

Why is knowing about fetal circulation after birth important to the RT?

Knowing about fetal circulation after birth is crucial for respiratory therapists (RTs) because it helps them understand the physiological changes that occur as a newborn transitions from fetal life to independent breathing. In utero, the fetus relies on shunts like the ductus arteriosus and foramen ovale to bypass the lungs and liver, as oxygen is supplied through the placenta. After birth, these shunts must close as the lungs begin to take over oxygenation. RTs need to recognize signs of abnormal transitions, such as when the ductus arteriosus remains open (patent ductus arteriosus, PDA) or the foramen ovale fails to close, both of which can affect oxygenation and require intervention. By understanding fetal circulation and its changes after birth, RTs can better monitor for respiratory or cardiovascular complications, anticipate the need for interventions like oxygen therapy, ventilation support, or medications like prostaglandin to manage ductal-dependent conditions.