Transition from Fetal to Neonatal Circulation

Mar 10, 2025

Mindmap

Fetal to Neonatal Circulation Transition

Introduction

  • Discussion on the transition of fetal circulation to post-birth circulation.
  • Focus on key changes after birth.

Key Changes After Birth

  1. Removal of Placenta:

    • Placenta is removed from baby's circulation upon birth - umbilical cord is cut and clamped.
    • Placenta, being a low-resistance pathway, is no longer part of circulation.

  2. Lung Utilization:

    • Lungs begin to take in air for the first time.
    • Oxygen levels rise, initiating several vascular changes.

Changes in Circulation

Removal of the Placenta

  • Umbilical Cord Clamping:
    • Clamp does not hurt since there are no nerves in the umbilical cord.
    • Wharton's Jelly contracts due to lower temperatures outside the womb, acting as a natural clamp.
  • Resistance Changes:
    • Transition from low-resistance placenta to high-resistance system post-birth.
    • Blood flow through umbilical vein and ductus venosus ceases.

Lung Activation

  • Fluid to Air Transition:

    • Alveoli replace fluid with air, reducing pulmonary vascular resistance.
    • Arterioles surrounding alveoli dilate, allowing easier blood flow.

  • Decreased Pulmonary Resistance:

    • Blood can flow easily to lungs due to decreased resistance.
    • Overall lower pressures in the right side of the heart.

Closure of Foramen Ovale

  • Pressure Changes:
    • Lower right atrial pressure allows closure of the foramen ovale flap.
    • Closure occurs within minutes after birth.

Ductus Arteriosus Constriction

  • Oxygen & Prostaglandin Influence:
    • High oxygen levels and decreased prostaglandin lead to ductus arteriosus constriction.
    • Constriction begins in early hours after birth.

Umbilical Arteries Changes

  • Resistance and Muscle Constriction:
    • High resistance and muscle constriction reduce blood flow in umbilical arteries.
    • Constriction happens over a few hours.

Summary

  • Transition from fetal circulation involves several adaptations occurring over minutes to days.
  • Each baby may experience these changes differently, but they are crucial for successful adaptation to life outside the womb.

These notes outline the physiological changes that occur from fetal to neonatal circulation, highlighting key concepts and mechanisms involved in the transition.