What your baby is like at birth

Before she is born, your baby is connected by the umbilical cord to the placenta. “It’s a bit like being on a bypass machine during surgery,” says Robin Walker, a London, Ont., paediatrician and former president of the Canadian Paediatric Society. “Within the placenta, oxygen and carbon dioxide can pass between the mother’s blood vessels and her baby’s blood vessels, doing the work of the lungs.”

Once your child is born and the placenta detaches, that bypass machine is instantly turned off. She takes her first breath, and her lungs—which have been small and folded up until this moment—start to inflate. After a few minutes of breathing, they are completely expanded, ready for their job of taking in oxygen and getting rid of carbon dioxide.

But another big change also has to happen. Until now, a blood vessel called the ductus arteriosus bypassed the lungs and sent the blood to the umbilical cord to get its next load of oxygen. With the lungs inflated, blood will now flow into the lungs to get oxygen, and the ductus arteriosus shuts down. Your newborn’s blood is now flowing in almost the opposite direction—up to the lungs rather than down to her belly button.

That change in blood flow affects your baby’s heart as well, explains Walker. “Before birth, the right and left sides of the heart are relatively equal in size and muscle strength. Once the lungs inflate, there is a big drop in pressure for the right side, so the left side becomes much larger and stronger for the rest of the baby’s life.”

On top of these dramatic shifts, almost every organ in your infant’s body goes through changes at birth. “These changes aren’t visible,” says Walker, “but they are major physiological and anatomic changes that adapt the baby’s body to life in the outside world.” For example, Walker explains: “The baby has been in a mostly dark and quiet environment. Suddenly she has things to look at, more things to hear and new experiences—leading to rapid brain growth and development.”

Before birth, your baby received all her nutrients through the umbilical cord. Now she has to quickly master sucking and swallowing, and her stomach and intestines have to start digesting food. Her liver and kidneys, which previously relied on the placenta to filter toxins and eliminate waste, have to start filtering her blood themselves.

“It is astonishing that all these huge dramatic changes that have to happen at birth do happen almost perfectly every time, quite naturally,” adds Walker.

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