The concept of a baby “breathing” while submerged in amniotic fluid often sparks curiosity. Fetal respiration is fundamentally different from how we breathe air. A baby in the womb does not take in oxygen through its lungs; instead, a complex system ensures a continuous oxygen supply for growth and development. This involves specialized organs and temporary circulatory pathways.
How Babies Get Oxygen Before Birth
Before birth, the placenta acts as the primary organ for oxygen delivery to the fetus. This structure, which develops in the mother’s uterus, facilitates the exchange of substances between the mother and the baby. Oxygen and nutrients from the mother’s bloodstream pass across the placenta to the baby’s bloodstream. Simultaneously, waste products, including carbon dioxide, are transferred from the baby’s blood back to the mother’s circulation for elimination.
The umbilical cord serves as the vital connection pathway between the fetus and the placenta. It typically contains one large vein, which carries oxygen-rich and nutrient-filled blood from the placenta to the baby, and two smaller arteries that transport deoxygenated blood and waste products back to the placenta.
Lungs in the Womb: Development and Practice
Within the womb, a baby’s lungs are not filled with air but with amniotic fluid, which is produced by the fetal lungs themselves. This fluid plays a significant role in promoting the normal growth and development of the lungs by maintaining them in a distended state. The lungs develop gradually throughout pregnancy, with key structures like alveoli, the tiny air sacs responsible for gas exchange, forming between 24 and 36 weeks.
Babies engage in fetal breathing movements. These practice breaths, which can begin as early as 10 to 12 weeks and become more consistent around 20 weeks, involve the inhalation and exhalation of amniotic fluid. This activity helps strengthen the respiratory muscles and supports the development of the lungs in preparation for breathing after birth. The lungs also begin producing surfactant, a substance that reduces surface tension in the alveoli, preventing them from collapsing once they fill with air.
The Big Change: Breathing After Birth
At birth, a physiological transition allows the baby to take its first breath of air. As the baby moves through the birth canal, the chest is often compressed, which helps to squeeze some of the amniotic fluid from the lungs. Hormonal changes during labor also trigger the lung cells to begin absorbing the remaining fluid.
Upon delivery, sudden exposure to a colder environment and tactile stimulation, along with the first cry, triggers the respiratory center in the brain. This leads to the baby’s first gasp, which inflates the lungs and replaces the fluid with air. This initial breath requires significant effort to overcome the surface tension within the fluid-filled lungs. As the lungs expand and begin to function, major changes occur in the baby’s circulatory system. Specialized fetal shunts, such as the foramen ovale and ductus arteriosus, which bypassed the lungs in the womb, begin to close, redirecting blood flow to the newly functioning lungs for oxygenation.