No, human babies do not develop gills while in the womb. Instead, they receive all necessary oxygen directly from their mother’s bloodstream. This involves specialized temporary organs and a unique circulatory system.
The Placenta’s Role in Oxygen Exchange
The placenta is a temporary organ that forms in the uterus during pregnancy, serving as the interface between the mother and the developing baby. It attaches to the uterine wall and connects to the baby through the umbilical cord. This vital organ acts as the baby’s “lungs, kidneys, and liver” until birth.
Oxygen and nutrients from the mother’s blood transfer across the placental membrane to the baby’s blood without the two blood supplies mixing directly. This exchange occurs through passive diffusion across villi, which increase the surface area for transfer. Simultaneously, the placenta removes waste products, such as carbon dioxide, from the baby’s blood, sending them back to the mother’s circulation for elimination.
How Babies Circulate Oxygen
The umbilical cord connects the baby to the placenta. It typically has one umbilical vein, which carries oxygenated, nutrient-rich blood from the placenta to the fetus. Two umbilical arteries then carry deoxygenated blood and waste products back from the fetus to the placenta.
Fetal circulation features unique shunts that bypass the baby’s lungs, as they are not yet functional for breathing air. One shunt is the foramen ovale, an opening between the right and left atria of the heart. This allows oxygenated blood from the right atrium to flow directly into the left atrium, bypassing the pulmonary circulation.
Another shunt is the ductus arteriosus, which connects the pulmonary artery to the aorta. This structure diverts most blood away from the lungs and into the systemic circulation. These adaptations ensure oxygenated blood is efficiently directed to the baby’s vital organs, including the brain and heart.
Preparing for First Breaths
Throughout pregnancy, a baby’s lungs undergo several developmental stages, including the canalicular and saccular phases, preparing for breathing air after birth. During this time, specialized cells begin producing surfactant, a substance made of lipids and proteins. Surfactant reduces surface tension within the tiny air sacs, called alveoli, preventing them from collapsing and allowing them to inflate easily with air after delivery.
Babies also engage in “practice breathing” movements while in the womb, beginning as early as 10 to 11 weeks of gestation. These movements involve inhaling and exhaling amniotic fluid, essential for strengthening respiratory muscles and promoting lung development. However, these movements do not provide oxygen to the baby.
At birth, a rapid series of changes transforms the baby’s circulatory system. The umbilical cord is clamped, and as the baby takes its first breaths, the lungs expand with air. This causes a decrease in pulmonary resistance, leading to increased blood flow to the lungs and the functional closure of the foramen ovale and ductus arteriosus, transitioning the baby to independent breathing.