Babies do not breathe air inside the womb. Their respiratory system functions differently during gestation than after birth. This raises questions about how they receive the oxygen necessary for their development.
How Fetal Oxygen is Supplied
A baby receives oxygen through the placenta, a specialized organ that acts as the baby’s “lungs” before birth. This organ facilitates the exchange of gases. Oxygen and nutrients from the mother’s bloodstream pass across the placenta to the baby, while carbon dioxide and waste products from the baby are transferred back to the mother for elimination.
The umbilical cord serves as the connection between the placenta and the developing baby. It contains blood vessels that transport oxygen-rich blood and nutrients from the placenta to the baby. Conversely, deoxygenated blood and waste products travel back to the placenta through the umbilical cord. Fetal hemoglobin, a specific type of hemoglobin present in the baby’s blood, has a higher affinity for oxygen than adult hemoglobin, which enhances oxygen transfer from the mother to the fetus.
Practice “Breathing” in the Womb
Although babies do not breathe air, they engage in fetal breathing movements. These movements involve rhythmic contractions of the chest and diaphragm. Instead of inhaling air, babies draw in and expel amniotic fluid, the liquid surrounding them in the womb.
These practice breathing movements are important for lung development and help prepare the baby for independent breathing after birth. They assist in the maturation of the lungs and strengthen the diaphragm muscles. Fetal breathing movements can begin as early as 10 to 11 weeks of gestation, becoming more frequent as the pregnancy progresses, reaching up to 30-40% of the time after 30 weeks.
The Transition to Air Breathing
At birth, a baby undergoes a physiological transformation to begin breathing air independently. As the baby moves through the birth canal, pressure on the chest helps to expel some of the amniotic fluid from the lungs. The remaining fluid is then absorbed by the baby’s body.
Upon birth, the baby takes its first breath, typically within about 10 seconds. This initial gasp is often triggered by sensory stimuli, such as the sudden change in temperature and the new environment. The lungs, previously filled with fluid and uninflated, begin to expand as air rushes into the tiny air sacs, called alveoli.
This inflation of the lungs causes a significant decrease in blood pressure within the pulmonary system. Simultaneously, the increase in oxygen levels in the blood triggers the closure of specialized shunts in the fetal circulatory system, such as the foramen ovale and ductus arteriosus, which previously diverted blood away from the lungs. These changes reroute blood flow, allowing it to circulate through the newly functional lungs to pick up oxygen and then be pumped throughout the body.