Babies do not breathe air while in the womb in the same way adults do. Their developing lungs are filled with fluid, and they rely on a different system for oxygen supply. Fetuses perform essential practice movements that prepare their respiratory system for life outside the womb.
How Babies Get Oxygen Before Birth
Before birth, a baby receives all necessary oxygen through its mother’s bloodstream. The placenta, an organ that develops in the uterus during pregnancy, serves as a crucial interface for this exchange, acting as the baby’s temporary lung, kidney, and digestive system. Oxygenated blood from the mother travels to the placenta, diffusing across a thin barrier to enter the baby’s circulatory system. This rich blood then flows to the fetus via the umbilical cord. The baby’s lungs are not involved in gas exchange at this stage, as they are filled with amniotic fluid.
Fetal Breathing Movements
While not breathing air, fetuses engage in rhythmic contractions of their diaphragm and chest muscles, known as fetal breathing movements. These movements typically begin around 10 to 12 weeks of gestation, becoming more regular as pregnancy progresses. During these practice movements, the fetus draws amniotic fluid into and out of its lungs. These movements are not for oxygen intake but are crucial for the development and maturation of the respiratory system. They help strengthen the muscles involved in breathing, such as the diaphragm and intercostal muscles, preparing them for independent breathing after birth.
The Role of Amniotic Fluid
Amniotic fluid plays a supportive role in the development of the fetal lungs. As the fetus “inhales” and “exhales” this fluid during practice breathing movements, it helps the tiny air sacs, called alveoli, within the lungs to mature. This continuous movement helps expand developing structures and promotes lung tissue growth. The presence of amniotic fluid provides a sterile, protective environment for lung development. Its mechanical action on the developing lungs ensures they are ready to function after birth.
Transition to Breathing After Birth
The moment a baby is born marks a profound transition in how it obtains oxygen. As the umbilical cord is clamped and cut, the baby’s oxygen supply from the placenta ceases, prompting the first breath. This immediate need for oxygen, combined with environmental stimuli, triggers a series of physiological changes. The baby’s lungs, previously filled with fluid, begin to inflate with air as the fluid is expelled or absorbed. The change in pressure within the chest cavity and the sudden influx of oxygen cause shifts in the baby’s circulatory system, redirecting blood flow to the lungs. Crying often accompanies these first breaths, helping to clear any remaining fluid from the airways and fully expand the lung tissue.