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.

.related-article-block{display:inline-block;width:300px;padding:.5rem;margin-left:.5rem;float:right;border:1px solid #ccc}@media (max-width: 525px){.related-article-block{float:none;display:block;width:280px;margin:0 auto 2rem}}
5 reasons why the last few uncomfortable weeks of pregnancy are worth it

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 i...